D EP AR
TMENT
C
O F
O MM E R C E
S CI ENTIFI C P AP ERS
O F THE
B U REAU
8
!
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S
S TANDARD S
OF
TRA TTO
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,
I R EC T O
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N o 400
.
I O NI! ATI O N AND RE SO NANC E P O TE NTIAL S O F
S O M E NO NM ETAL L I C EL E M E NT S
B!
MOHL ER Associate P hysicist
FOOT E Physicist
P AU L
F L
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.
,
,
B u r eau
f S tandar ds
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O CT O B ER 14, 1 9 20
NT S
P RI C E, 5 C E
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1920
I
O FF C E
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g O fli ce
IO NI!
A TIO N AND RESO NA NC E PO TENTI AL S
NO NM ETA LL IC EL EM ENTS
By F L M o hle r
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CO
I
II
III
OF
SO M E
d Pau l D Foo te
an
.
NTEN TS
P
a ge
6 69
.
.
M e asu r e m ents in th e
.
v a o r s of
p
ph os ph or us
io d ine ,
,
and s u l
ph u r
6 73
6 74
3
IV
.
V
.
S p e c tr al
I
3
VI
.
r e l ations
.
Intro d u c tion
.
O x ygen
.
o8o
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.
I
.
IN
T RO D U C T I ON
The methods prev i ously app lied b y the authors to the study of
critical potentials in the metalli c vapors have been with some
m o d ificat i ons use d for the elements phosphorus i o d ine sulphur
nitrogen oxygen an d hydr ogen A study of the phenomena of
electr on currents inthese polyatomic nonmetallic elements can be
best intro duc e d b y a statement of the essentia l features of electr on
impacts with metal l ic vapors s inc e work with these has yie lde d
r esults of consi derabl e accu r acy an d of a d efinite theoret ic a l si gnifi
canoe
Coll isions of low speed e lectrons w ith metallic molecu les are
e lastic b ut with higher speeds two types of ine l astic impact occur
I
( ) When the ve l ocity in vo lts is greater than the resonance
potentia l c ollisions are ine lastic an d the ve locity lost at c ollision
is equa l to the resonanc e potential V
The c orrespon ding energy
V e is radiate d as l ight of a single frequenc y V re l ated to V by the
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ran ck
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16 pp 45 7 and 5 1 2 1 9 1 4 Tate and F oote J ! as
H e rtz V er h D e t
s ! es
Aca d
ci a pers No 3 1 7
il M ag 3 6 p 64 1 9 1 8 F oot e and M o ler
hi l M a g
Sci 7 p 5 1 7 1 9 1 7; B S
3 7 p 3 3 1 9 1 9 ; J ! as
ci 8 p 5 1 3 1 9 1 8 Foote Rognl ey and M o ler ys R ev , 13 , p 59 ,
Aca d
19 19
ci a pers No 3 68 F oote and Meg g ers B
ape rs
M ahle r Foote and timso
B S
S ci
No 3 86 Ab stra cts of parts of th e prese t paper ha e a ppeared in O p t Soc Am J 4, p 49 , 1 9 2 0 and h ys
R ev , 15, p 3 2 1 , 1 9 20
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S P
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h P
Ph
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669
P
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Scientific
6 70
P a p er s
f
o
B u r ea u of S ta nd a r d s
the
quantum relation V e hp This spectrum l ine is the first member
of an absor ption series in the spectrum of the metal ( 2 ) When
the ve lo c ity of the colliding e lectron is gr eater than the ionization
potent ial V 1 the molecu le is i onize d and the energy lost b y the
e lectron is expended in removing an electron from the mo lecule
I n accordance with the Bohr theory of spectr a the frequency 1
=
correspond ing to the quantum equation V ie hv is the limiting
frequenc y of the absorption series
I n some cases we have foun d
two resonance potentia ls and as will be shown in a subsequent
pub l ication this is a characteristic property of metals of Group I I
in the perio d ic tab le
Data at present available on electron currents in nonmetal l ic
ases
an
d
vapors
i
ndicate
that
the
phenomena
here
obse
e
d
a
r
e
r
v
g
more comp l ic ated I t is believed that in these elements collis ions
at all ve l o cities are somewhat inelastic and that there i s a tendency
for e lectrons to st ick to mo lecules and form negative ions of large
mass
S pectroscop i c data available for these elements give no su g ge s
t i on of the probable va l ue of critica l potentials No observations
of spectr a of g l ow discharge below the ionization potential have
been made S ome of the vapors show very complicated ab s or p
t i on spectra in which bands lines and regions of continuous
absor pt i on o ccur wh ile the gases n itrogen and hydrogen in the
nor mal sta te give no certain evidence of absorption in the regions
which it is poss ible to study No l ine series have been foun d in
any of the vapors
S ome of the diffi cu lties in measur ing the critical potentials can
b e foreseen In metallic vapors wh ich g ive elastic collisions with
low speed electr ons we can determine the l owest potential of
inelastic impact with a ccur acy b y increasing the vapor density
unti l the mean free path of electrons is s o small that electron
ve locities can never m uch excee d the first resonance potential
H owever when low spee d collisions are slightly ine lastic cu rrent
m easur ements must be made in a limite d range of vapor density
Critical points will not be so sharp and successive inflect i ons in
current vo l tage curves due to t w o resonance potenti als may be
m istaken for recurrence of collisions of one type on ly
The greatest diffi culty in study ing electron currents in the
vapors however w as the form ation of nonconducting films on the
electro des resulting in polarization eff ects This cou ld be on ly
partia l ly remedied
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F
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r n ck
a
and
H ertz
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P hy
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it
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1 7 , p 40 9 ,
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1
91 6
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ggf
l h
o
I oniz a tion
'
t
a nd
Res ona nce P otentia ls
II M ET H O D S
OF
.
6 7I
MEA S U R EME NT
The type of ionization chamber used in the study of metallic
vapors w as modifie d by the addition of a fo ur th electr ode for the
more sensitive detection of potentials of inelastic impact Fig I
shows diagrammatically the arrangement of the electrodes S ur
rounding the hot wire cathode A and as close to it as was con
venient ly p ossible was a grid B an d a secon d gri d C was place d
close to the outer electr ode D O f the many ways these four
electro des can be c onnected for the measurement of the various
phenomena of e lectron currents in gases three at least deserve
at tention
M etho d 1 Fig I A variable ac celerating potential V is applie d
between A an d B B an d C are kept at the same pot ential and a
retarding fie ld is fixe d between C an d D Thus through a c ons id
er ab le range of gas pre s sure ele c trons w ill be given their full velocity
in the space AB before colliding Iwith molecul es in the larger part
o f their path B C
As there is no radial electric force in the space
B C elec trons w il l be kept from reaching the plate by elastic colli
sions changing their direc tion as well as by inelastic collisions
c hanging their speed an d high gas pressur e will greatly decrease
I f V is fixed at a comparatively small value
th e plate current
the change in the partial current reaching the plate as the accel
er a ting potential V is varied gives rem arkably sensitive indica
t ions of potentials of inelasti c impac t
At voltages equal to or twi ce or three times the resonanc e
potential the plate cur rent decreases on acc ount of th e fact that
elec trons undergoing one two or thr ee inelastic collisions between
the grids lose all their velocity an d are kept from the plate by the
retarding fiel d V
S topping of the current is probably enhance d
by the space charge that must exist at potentials w here electrons
are entirely stopped betw een the grids
When the potential V is made greater than V ionization c an
b e detected by the Lenard method ; that is by observing the point
at which current due to positive c harges flows to the plate when
V is increase d
l
While m etho d I o ff ers a sensitive metho d of measuring points
of ine l astic impact it is also sensitive to disturbing e fi e c t s o f polar
iz ed s u rf ace films an d it c an be use d only w ith limite d range
o f vapor density
M ethod 2 Fig 2 The inner grid B is kept at a fixe d relatively
small potential V with respect to the catho de w hile the poten
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0
Scientific
6 72
P a p er s
f
o
the
B u r ea u of Sta nd ar d s
[ Vol
.
16
tial V of the outer grid is changed A retardi ng field as before
is place d between the outer grid and plate P late currents when
V is small sho w the points of inelastic impact but not as sharply
as in method I at l ow gas pressur e Disturbing effects are much
diminis hed Ionization can be detected as in method I by making
I
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2
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( )
2
(3 )
FI ! S
.
1
,
2
,
an d
3
—
.
E le c tr ica l
co nnec tio ns
f
or
m e tho ds
I
,
2
,
a nd
3
,
respectively
.
greater than V
It can also be observed by meas u ring the
total electron current reaching the outer grid an d plate since this
will increase at the ionization point It may be noted that while
the current leaving the cathode is nearly constant as V is change d
the part of the current getting thr ough the inner grid increases
as V is increased
V2
1
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I
I
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,
I oniz a tion
a nd
6 73
Res ona nc e P otentia ls
Davis and Goucher have sho wn that with an ionization c ham
ber connec te d by the Lenar d metho d viz V greater than V in
either metho d I or 2 ra diation emitte d in the glow di sc harge at
the resonanc e potential may g ive a photoe lectr ic current b etween
the plate an d outer gri d in distinguishable in these metho ds of
measurement from the current due to ionization The follow ing
metho d of distinguishing ionization an d radiation IS practic ally
i dentical with the metho d use d by them
M etho d
Fig 3 The v ar iable accelerating potential V is
applie d betw een the c atho de an d the inner gri d The outer gri d
is kept at a potentia l V an d the plate a t V V
Thus no
el ectrons from the catho de c an reach the p l ate I ons forme d near
th e inner g r i d will reach th e pl ate after falling thr ough the poten
tial
( V V2) in spite of the relatively small r etar ding field V ;
b ut pho to e l ec trons emitte d from the gri d an d p late w ith a small
velocity w ill give a current in the direc tion of V an d opposite to
3
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2
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l
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2
2
3
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3
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3
M easur eme nts with metho d 3 have not in our han ds given
nearly a s ac cur ate resul ts as c an b e obtaine d from measure ment
of the p arti al cur rent reac hing the p late against a s mall retar ding
fiel d but the metho d was useful in distingu ishing ionization an d
radi ation eff ec ts in hydr ogen M easurement s by the Lenard
metho d with c onnections of metho d 1 g ave muc h sharper inflec
tions at the criti c al potentials for both radiation an d ioniz ation
,
.
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HI M EAS U REM ENT S I N T HE VAP OR S O F P HO S P H O RU S ,
'
.
I O D I NE,
AND S UL P HU R
\
Disturbing eff ects of sur face films on electro des presente d the
c hief difficulty in this work . Frequent renew a l of the elec tro des
a nd suitable choic e of materials reduc e d the trouble but d id no t
eliminate it R esonanc e potentials were measure d from su c c e ss w e
infl ections in the p late current curves obtaine d by metho d I o r 2
I oni zation potentials were measu re d by the Lenard metho d with
the same galvanometer sensitivity as use d for the resonanc e cur ves
and w ere correcte d from the observe d initial potent ial oi the
resonanc e curve As the observe d ionization point depends s ome
what on the galvanometer sensitivity it is necessary to keep this
the s ame for the t wo cu rves
The form of vacuum tube used w as a large pyrex tube 8 by 3 0
cm closed at the bottom an d with a metal plate supp orting the
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3
Ph
ys . R ev
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10,
p
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101 ,
1 9 1 7.
Scientific
6 74
P a p er s
f
o
B u r ea u of Sta nd a r d s
the
electr odes sealed in the top Electrodes o f sheet steel an d iron
gauze w ere use d w ith phosphor u s while nickel an d an inner gri d
of p latinum w ere used in iodine With sulphur a plate of alu
minum and grids o f platinum gave best resul ts
The plate in
eac h c a se w as a cylinder fitting the pyrex tube an d the other
electrodes w ere in the p roportions shown in Fig 1 The cathode
use d in phosphorus and iodine w as usually a bare i ncandescent
molybdenum w ire as oxide coatings were attacked by the vapors
an d w ere practically useless for increasing thermionic emission
P latinum s trip s c oated w ith burned sealing w ax were satisfact ory
in sulphu r vapor The temperature of the tube w as contr olle d
by baths of ice or w ater or by an elec tric furnace surrounding
the lower part o f the tube I t w as always nec e s s ar y t o keep the
elec tro des at a higher temperature than the rest of the tube to
avoi d the c on densation of an ins u lating layer on them A vacuum
mm w as maintained by mercury vapor pumps an d
o f about
a trap cooled in liqui d air or carbon dioxide snow w as plac e d
between the pumps and ionization chamber C u rrents w ere
meas u re d on a sensitive galvanometer and were of the order of
amperes
10
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—
8
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1 . P HO S P HO R U S
Fig 4 gives typical curves obtained with phosphorus vapor
using the fir St method of measurement Curves 1 9 2 2 2 8 3 1
an d 3 8 are the electron cu rrent reaching the p late against a small
retarding field Curves 6 9 and 3 2 are of positive cur rent reac h
ing the plate when the retar ding fiel d is l ar ge V iz the Lenar d
method Table I gives the results of all the curves obtained w ith
notes on condi tions of observation From the curves shown it is
Seen that phosphorus has a definite resonance potential The
ionization point is not very sharp but is unmistakable Attempts
to obtain more inflections in the partial c urrent curves by in
creasing the vapo r density reduced the current to an immeasurable
value
The curves w ere obtaine d u nder a wi de range of conditions as is
Shown in Table 1 Curves 6 9 1 9 an d 2 2 of Fig 4 w ere obtaine d
in the vapor of yellow phosphor us at about room temperature
U nder these c onditions the vapor con denses in the form of a re d
film evi dently a mixture of re d and yellow phosphor us Curves
2 8 and 3 8 w ere obtaine d in the vapor o f re d phospho r us at about
00
4 C At this temperature the vapor condenses in col d parts
o f the tube in a re d film as before an d in the hot p ar t in a gray
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°
.
I oniz a tion
crystalline form
a nd
Res ona nce P otentia ls
6 75
once heating re d phosphor us to about
0
C
getting
the
red
film
on
cold
pa
r
ts
the
tube
vapor
o
f
45
pressures suited for cur rent measuremen
ts were obtaine d in a
wide range of temperat ure Curves 3 1 and 3 2 were obtaine d at
room temperature after the tube ha d been heated The similarity
of all the curves in the temperature range 42 0 C to I 5 C indicates
that the constitution o f the phosphorus molecul e in the vapor
After
.
°
,
'
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.
°
°
‘
t
n
e
r
r
o
t
FI !
.
4
.
—
C u r r ent- vo
'
lta ge
cu rves
f
or
s
h
o
u
s
r
h
o
p p
state does not change in this range The molecular constitution
of phosph orus vapor at 3 0 0 C is given as P
The mean values from the 43 curves are summarized as follows :
.
°
,.
vats
5
.
AS can be seen from Table
I
the individual measurements of
resonance potential do not differ from the mean by more than the
I
,
Scientific
6 76
P a p er s
f
the
o
B u r ea u of Sta nd a r d s
[ Vol
.
16
probable observational error b u t there is more variation in the
ionization potentials probably arising in the method of applying
initial potential c orrections A striking feature of th e par tial
current curves is the lar ge initial potential correc tion ; that is the
difference bet ween the reson ance potential an d th e applied
potential at the first resonanc e point Clearly it is not a velocity
correction in this case but probably a c onta c t d ifl er enc e of poten
tial betw een the catho de an d gri ds due to the formation of a
phosphide film on the latter A S imil ar though smaller positive
correction w as ob serve d in the other vapors Another possible
interpretation of the initial potential c orrection is mentioned
later
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I O D INE
2.
Fig 5 gives some typical curves obtaine d in io dine va J or
Table 2 gives results of all curves obtained Curves I 6 a nt 2 2
are the par tial electron current reaching the plate as measure d by
metho d I Curves 1 3 I 7 an d 2 5 were obtaine d by metho d
an d curves 4 an d 6 Show the ionization current by the Lenar d
metho d The satisfactory temperature an d vapor pressure range
was much smaller than in the case of phospho rus
Temperatu res
from 5 C to 3 0 C were tried but the best results w ere obtaine d
near 2 0 C The vapor pressures observe d by Baxter Hickey
and H olmes in this range ar e : 0 C
mm ; 1 5 C
mm ;
25 C
mm The molecul ar constitution of iodine vapor is 1
Efl e c t s of po l arization due to films on the electr odes were most
Curves I 6 an d 2 2 illustrate this effect
troub lesome for iodine
The decrease in the current b eyond the fir st resonance potentia l
was in many cases much more marked but inflections b eyond the
first resonanc e point were then too faint for measurement The
polarizati on gradually increase d with time s o that the electro des
had to b e renewe d frequently The eff ects were most m arked at
high vapor pressure The curves obtained by metho d 2 Show the
effect much less than metho d I
The fact that the curves obtained under various conditions
give values of the resonance potential not varying from the mean
by more than the probab le uncertainty of picking out the points
of infl ection on the cu rves is good evidence that this method of
measuring the resonance potentia l is reliab le unti l disturbing
eff ects entirely mask the infl ections due to inelastic imp act
M easurements of ionization potential as in the case of phosphorus
i
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,
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,
-
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°
°
,
°
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,
°
°
4
,
,
,
°
2.
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ur
Jo
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mr
A
e
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C
hm
e
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Soc
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,
29
,
p
.
1 2 7;
1 90 7.
fig
I oniz a tion
"
a nd
Res ona nce P otentia ls
6 77
Show a larger observational error though the percentage error is
probably less The mean values are as follows :
V lt
.
s
o
anc e
R eson
Ioniz ation
pote ntial
po tential
2
.
3 4i
1 0. 1
.
d:
0. 2
5
Th is is the first measurement that has been made of the r es on
ance potentia l The ionization potential has been meas u red
.
Vo lt s f or C li nics
FI !
.
5
—
.
“nae
C u rr ent-ao ltage
cu r ves
f
or
iodine
by C G Found from the c urrent voltage curve obtaine d in a two
electrode tube as 8 5 vo lts
he presence of a contact potenti al
difference of about I vo lt obser ve d b y u S but of course impossib le
to detect in a two e lectro de tube would exp l ain the d ifference
5
.
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.
_
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-
,
5
P hy
s.
R ev
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,
15 ,
p
.
1920.
6 78
Scientific
P a p er s
f
o
the
B u r ea u of S tand a r d s
[ V ol
.
16
3 . S UL P HU R
Table 3 gives the results obta ine d in sulphur vapor and Fig 6
shows some typic al curves Curves 3 2 2 and 2 6 Show the par tial
electron current reaching the plate as measured by metho d I
Curve 3 0 shows the same obtained by method 2 Curves I I an d
“
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,
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,
,
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12
IO
Vo l t s
FI !
.
6
—
.
C
u rr nt v lt g u r
e
-'
o
a
e c
ves
f or
s
u lph
u
r
Show the ionization point by the Lenard method Meas u re
ments were made in the tempera tu re range 1 2 0 C to 1 70 C
The probable molecular structure of the vapor is S
D iffi culty with unsteady currents was a source of trouble in
these measurements but this unsteadiness gr adual ly decreased
if the temperature was held constant for some time The cause
1
6
.
°
°
.
8.
.
,
I oniz a tion
a nd
R es ona nce P otentia ls
6 79
this was unknown As can be seen from Fig 6 the curves Show
infl ections capable o f fairly accur ate measurement but unlike
the other vapors the agreement between results from diff erent
curves is scarcely within the probable error in picking out the
I
t
oints
can
be
seen
from
the
fig
u
re
that
in
some
the
curves
o
f
p
the Second resonance inflection is not ha lfway bet ween the first
The existence of two resonance potentials is a probable
a nd th ird
exp l anation Determination of the ionization potentia l gave as
c onsistent results
as the other elements An unpublished r e
s earch by Foote and R o gnley on the ion i z ation poten ti a l in which
in itia l potential corrections were made from velocity distribution
curves a l so gave a result in close agreement with the results of this
w ork
The fina l summary for sulphur is as foll ows :
V lt
of
.
.
,
,
,
.
.
.
.
.
o
R e sonanc e
pote ntial
5
4
.
12
Ioniz ation po t ential ( Foote
IV
s
R ognle y)
and
S P E C T RA L
.
12
.
2
.
1
:;
5
1
R EL ATI ON S
From ana l ogy with the metal l ic vapors the reson ance potential
=
e
shou l d correspond by the quantum re l at i on V hr to the fr e
n
o
e
c
f
the
sing
l
e
l
ne
spe
c
trum
The
o
l
lowing
wave
l
engths
u
f
i
q
y
are computed from the resonance potentials :
-
.
P hosphorus A
2 1
I odine
A
0
0
53
Sulphur
A
2
30
5 80
A
A
A
It has not been possib le to identify these predicted l ines from
s pectroscopic data available at present
The absorpt i on spectrum of phosphorus has not been stud ied
b eyond
I n b oth iodine and sulphur t h e pred icted l ine
lies in a regi on of comp l icated band spectra and at least in the
se of io d ine in a region of line absorption spectra as well but
ca
w ith l ines c l oser than the probable error of our meas urement
P robably in the case o f phosphorus a lso the pre d icted l ine l i es
w ithin a w i de region of band Spectra as bands are observed to
the limit of the region photographed
.
7
8
,
-
,
,
.
.
,
.
.
‘3
7
K
R
a
.
y
se
!
.
i
r
!
d
an
oo
8 D obb e and
Ru
ng e ,
Ha
nd b u c h
J ur 46
.
d Ast r op h ys
,
F ox
,
Pr c
o
.
.
o
.
,
R oy . S o c
.
,
,
p
1
81 ;
1
9 1 7.
nd n 9 5
.
Lo
o
,
,
p
.
484;
191 9.
Scientific
6 80
V
P a p er s
f
o
MEA S U REME NT S
.
1
.
the
B u r ea u of S tand a r d s
I N T H E C O MM ON !
[ V OL
16
A S ES
IN TR O D U C TI O N
four electrode vacuum tube of the same general form as
described in Section II was used to study electron cur rents in
nitrogen oxygen and hydrogen The ionization chamber was
made of platinum electrodes sealed in a glass tube about 3 cm
in diameter The gri ds were of fine plat inum gauze supported on
heavier str ips and the p late was a cylinder of platinum foi l fitt ing
tightly in the tube A hot p l at inum strip coated with bur ned
sealing wax served as a cathode Connecting tubes to the pump
and the gas reservoir were arranged so that gas could be streamed
through the tube or kept stagn ant while liquid air tr aps on each
s ide of the ionization chamber froze out any condensab le impur ities
In the study of electron currents in these gases we are able to
consider another effect of collision besides loss of electron velocity
and ionization namely the effect of radiation emitted above the
resonance potential on the outer electrodes causing photo electric
emission from them As the long wave length limit of p l atinum
is about A= 2 80 0 A this c fl e c t must be presen t whenever the
resonance potential is a bove
volts but with our apparatus it
has been too small to measure in all the elements prev i ously
studied The radiation eff ect has further interest in research on
the gases since in most o f the considerable amount of work of
other observers the resonance potentials have been obser ve d by
means of the radiat ion effects
The Lenard method as used in Section II for the meas u rement
o f ionization potentials ! ill Show th is radiation e ff ect at the
resonance potential as a current in the same direction as the
ionization current Davis an d Goucher dev ised a method de
scr ibed under method 3 for dist inguish ing eff ects of radiation an d
When precautions are taken to dist inguish the two
ionization
e fl e c t s we have a valuable means o f measuring critical potentials
which is entirely dist inct from the method of inelastic collisions
here used However in all the work previous to the research of
Davis and Gou cher the simple Lenard method was applied w ith
the assumption that the presence of a plate current was conclusive
evidence of ionization The uncertainty as to !ust what was meas
u r e d accord ingly vitiates nearly all this ear l y work
A
-
.
,
,
.
,
.
.
-
.
,
,
,
—
,
,
-
.
,
,
.
,
.
9
.
.
,
,
.
,
.
.
9
Ph y
s.
R ev
.
,
1 0,
p
.
84 ;
1
9 1 7.
a nd
I oniz a tion
2
.
R es ona nce P otentia ls
6 81
"
NITR O ! EN
observers using the Lenard method have given values
of about 7 5 vo lts for th e ioni z at ion potent i al of nitrogen Dav is
and Goucher have by their method found radiation alone at
volts further rad iation at 9 vo lts and ionization at 1 8 volts
H D Smyth has used the radiat i on method in a thr ee electrode
t ube making carefu l correct i ons for in itia l potentia l with the fo l
lowing results : R adiation
volts ; a secondary radiation effect
at
volts ; and ionizat ion 1 8 volts Found using a two
e lectrode tube observed ionization at about 1 6 volts Ake s s on
has applie d the method of observing the potentials of inelastic
c ol l isions but under quite different conditions from those we have
used and obtaine d the value of
vo lts
I n our work commercial nitrogen w a s pas sed thr ough hot copper
c a lcium ch loride and l iquid air traps P ressures ranging from
mm to 2 mm were used S tream ing gas was used where pos
s ible but at the higher pressures currents were steadier in stagnant
gas The D avis and Goucher method was app l ied with results
agree ing rough ly with theirs but the curves obtaine d were not
Sharp enough to furnish accurate va lu es of the critical potentials
M easurements with conn ections of method I proved capable of
much higher accuracy M easur ement of the total current with
method 2 gave a va luable check on the other ionization potential
measurements Tab le 4 g ives a summary of all the curves ob
t a ine d which were capable of accurate analysis
A1 1 upper l im it to the g a s pressure that c an be used is se t by
the striking of an arc between the cathode and inner net but
arcing between the nets at l ower pressure has a lso been found
troublesome when the current density is large The arcing poten
tia l is above the i on i zat i on potentia l and the amount above and
the sharpness increase with the pressure I t is indicated by a
break in the current voltage curves ver y sharp in contrast w
ith the
critical points Evi dent ly when the proportion of positive ions
formed by co l lision reaches a defin ite value the negative space
charge surround ing the cathode is suddenly replaced by a positive
space charge The resulting increase in the electr ic force at the
su rface of the cathode causes a sudden increase in the thermionic
emission It is possib le that the high valu es obtaine d for the
ionization potential by Davis and Goucher an d by Smyt h are due
V arious
«
.
1"
,
,
,
‘1
.
-
.
,
,
,
12
.
,
,
’3
.
,
,
.
,
,
-
.
,
.
,
.
,
.
.
.
.
,
.
,
.
.
.
.
1° P h
1‘
.
R ev
.
s.
R ev
.
yS
Ph y
,
13 ,
,
1 4,
p
p
.
.
1
;
1 9 19
40 9 ;
‘2
.
1 9 19.
‘3
Phy
s.
L
und
s
R ev
.
,
1 5,
p
.
1
32 ;
1
9 20
.
U niver s it e ts A r sskrift
N
.
F Avd
.
.,
2
Bd
.
: 2
N
11 1
.
Scientific
6 82
P a p er s
f
o
the
B u r ea u of Sta nd ar d s
[ VO L 1 6
to mistaking the arc point for the true ionization point A char
urve
ac t er ist ic feature of this ar e point is that the break in the c
as the potential is increased is above the break when the potentia l
This resu lt is in accord with the explanation given
IS decrease d
above
.
.
14
.
V ol t s
'
acc ele r ot ih
Th o 7
g
C u r r ent-a o ltag e
—
.
cu r ves
f
or
r
nit ogen
Fig 7 shows some typical curves Curves I I and 3 1 are plate
current as potentia l using connections of method 1 with V small
They Show inflections due to successive resonance collisions of
only one reson an ce potential A Slightly higher secon d resona nce
.
'
.
2
,
.
.
1‘
F oo
te
,
R og nl e y
and
h
r
M o le
,
lo c
.
cit
.
n
H orto
a nd
Da
vi Pr
es,
c
o
.
R o y . So c
.
,
3 7,
p
.
1
;
1920
.
Scientific
6 84
P a per s
f
o
the
B u r eau of Sta nd ar d s
!
.
.6
The phenomena of electron currents in oxygen are quite diff erent
fr om nitr og en though the c ritical potentia l s are in th e sam e r egion
The radiation c fl ec t is very small an d the point at whic h it starts
d ifli c u lt to determine though the points of inelasti c c ol lision ar e
nearly as shar p as in nitrogen Arcing above the ionization poten
tial w as not obser ve d in the entire range of pressures that c oul d b e
used an d no visible glow was observed in the vac uum t u be
However the i onization potential was very distinct in c ontr as t to
the ra di ation effect and o f a magnitude c omparab le to the e lectron
'
.
,
.
.
,
'
,
FI !
.
8
.
—
C
ur
rent
vo l ta ge c
-'
ur
ves
f or
ox
ygen
current The measurements o f critical potentials were therefore
made as w ith the vapors viz by obtaining tw o consecutive p late
current voltage curves by metho d 1 one with V small Showing
points of inelastic impac t an d one with V l arge showing ioniza
tion and by measuring from th e two the resonance potential and
the di ff erence betw een the ioni zation and resonance potentials
Tab l e 5 gives a summary of the conditions of measurement an d
analysis of all the cur ves Fig 8 gives typical curves The
accuracy attained w ith o xy
gen is probably slightly higher than
w ith nitrogen on account of the absence of arcing e ffects
.
,
,
.
2
,
2
,
,
,
,
.
.
.
.
.
I oniz a tion
The final values
a nd
R es ona nce P otentia ls
685
as follows
ar e
V lt
s
o
R esonanc e
Ioniz ation
pote ntia l
potential
79
.
1
i
.
5
The resonance potential gives by the quantum relation A I 56 0
A for the single line spec trum an d A 79 6 A for the limiting fr e
quency The wave length A 1 56 0 falls within the gr eat oxygen
band at A 1 800 to 1 3 00 A No line spectra have been observe d
with certainty in this region
-
.
‘
.
.
.
N
H! D R O ! E
4.
The value of th e critical potentials in hydrogen is of pec uliar
7
interest Si nc e the development of the Bohr theory However
th e fundamental theory pre dicts the potentials fo r onl y the hy dr o
gen atom An extension of the theory has been ma de by Bohr
h
a
l
e
D
e
e
the
c
ase
of
no
r
m
mo
l
c
e
but
this
H
e
b
u
l
b
an
t
e
o
t
2
y
d y
extension invo lves assumptions not inc lude d in the fun damental
theory an d it may b e opento even greater d oub t
iz e the hydr ogen atom in the norm al c on dition i e w ith
To ion
its single electron in the innermost stable orbit requ ires an amount
of wo rk propo rtion al to the R y db erg number o r a potential o f
vol ts
The work requ ire d to remove the e le ctron from the innermost
orb it to the next stable orb it is proporti onal to three fourths of the
volts
Rydb erg number g ivm g a resonance p otential of
The R y dberg number an d three fo ur ths of this number are
respe ctive ly the li m it an d first line of the Lym an ser i es As to
the hydr ogen mo lec ule the Bohr mo del in wh i ch the t wo electrons
revolve in c op lanar orbits aroun d the line !oining the two nuclei
as an ax is requires for i onization an amount of work equa l to the
ionization potential of the atom plus the work of d issociation of
His theory gives this ionization potential as 1
the molecule
volts m aking the work of d isso c iation
volt s Langmuir s
experimental determ ination of t he heat of d issoc iation of hy drogen
as 90 000 calories per gram molecule gives the work of dissociation
as
vo lts Bohr s theory of molecular hydrogen does not pre d ict
the value of a resonance potential for the molecule
Ex per imm ta l determ inations of the critical potentia ls of
hydr ogen have in the past seemed irreconcilable w ith this theory
Lenar d M ayer Bishop and others found ionization at 1 I volts
8
using the simple Lenard metho d Davis and Goucher by their
1
.
,
.
,
.
,
,
,
.
.
,
.
,
.
3
-
.
,
-
,
.
,
,
.
’
.
,
-
’
.
.
.
,
,
,
1
.
17
‘3
Phil
P hy
.
M ag
s.
.
,
R ev
.,
26 ,
18,
pp
p
.
.
1
,
84:
476 , 85 7; 1 9 13 .
1 9 1 7.
Scientific
6 86
P a p er s
f
B u r eau of S ta nd a r d s
the
o
[ Vol
.
ro
metho d found besides ionization at 1 1 volts a second ionization
at 1
volts an d radi ation at
volts M or e recently Frank
K nipping an d K ru ger
have by a similar metho d found ionization
at I
volts
volts an d
vo lts an d rad iation at I
volts
S ince our work descr ib e d b elow was complete d a paper by H orton
an d Davies has appeare d in which they have ar rive d at c onc lu
sions simi l ar to those obtaine d in depe n dently b y us an d much
more in accord with theory They fin d rad iation alone at
volts further rad iation at
vo lts ionization at 1 44 volts
an d
volts
The problem of d istinguishing and measur ing these four p oten
t ia ls which occu r in the interval 1 0 t o 1 7 vo lts is c onsi der ab ly m ore
d ifli c u lt than the measurements in other gase s show in g only two
critica l points
I n our work elec trolytic hy dr ogen was drie d as b efore an d either
streame d through liqui d a ir trap s or kept stagnant while readin gs
were taken The ionization chambe r was use d in the s ame form
as before an d also with c atho des of pallad ium str ips an d bare
tun gsten wire Also a much l arger ioni z ation c hamber with nicke l
e lectrodes similar to the one use d w ith the vap ors was tr ied
R esults obtaine d un der these varie d c on d itions were not notab ly
,
,
.
19
,
,
,
,
2"
.
,
,
.
.
,
-
.
.
.
preliminary experiments method 3 the Davis and Gouc her
metho d was use d to di stin guish radi ation and ion i zation eff ects
b ut with results quite contrary to theirs At ab out 1 0 volts a rad ia
tion eff ect al one was ob se rved and there was a strong ionization
eff ect at 1 6 volts By decreasing the gas pressure an d cou se
quently the rad iation efl ect the i onization efl ect c ould b e detecte d
at a lower point ar oun d 1 3 volts The curves ob taine d by this
metho d were not sharp enough to give accurate values for the
critical potentials The metho ds use d with the other gases
namely measurement of inelas tic imp acts b y method 1 and of
ionization by the Lenar d method with c onnections of metho d I
were applie d as b efore for the measurement of the potenti als
Fig 9 shows the types of curves o b tained Curves 3 7 64 6 5
an d 1 8 Show points of ine l ast ic impact whi le 54 3 0 an d 3 1 Show
curves obtaine d b y the Lenard metho d The c urves Show many
variations as pressur e and current density are changed Thu s
cu rves 1 8 and 6 5 Show two Successive resonance c ollisions near 1 0
In
,
,
.
,
.
.
.
,
,
.
.
.
,
,
,
,
,
.
.
'
1’ B er
’0
Pr c
o
.
D
.
u t Ph y
e
.
R oy S oc
.
.
s.
:
!
es . ,
21,
h
M arc
,
p
.
1 9 2 0.
72 8:
1919.
,
e
gg
I oniz a tion
"
a nd
R es ona nc e P otentia ls
6 87
and 2 0 volts an d between these points a sharp break due to the
second ionization potentia l Curve 6 4 shows inflections due to
the first resonanc e potential alone while 6 5 shows a definite ly
greater interval between infl ections which probably measu res a
sec on d resonance potential Curves of this latter type could b e
ob taine d on ly under a small range of conditions U nfortun ate ly
.
,
.
.
Vol t 8
.
o r:
FI !
9
.
—
,
C u r r ent-vo ltage cu r ves f or hyd rogen
pp ar atu s and method d i d not serve to separ ate
re sonance p otentials so as to measu re b oth from the s ame cur ve
M any of the cu rves s howed a broadening ou t of the inflection near
2 0 vo lts th at m ay b e w e l l e xp l aine d b y the su p erp os e d efl ec t of tw o
resonance potentials C u rves 6 4 and 6 5 S how th is efiect to a S l ight
our
a
.
Scientific
6 88
Cu rve
P a p er s
f
o
the
B u r ea u of S ta nd a r d s
[ V ol
.
16
was taken with the Lenard method using high gal
vanom e t er sensitivity and shows the radiation eff ect starting at 9
volts and the fir st ionization point at I 2 5 volts O nly a few curves
could be obtained showing both these points sharply
Curve 3 1 was taken under the same conditions except that the
galvanometer sensitivity was much less so that the radiation effect
was immeasurable It shows both ionization po ints Curve 54
is another of the same type
Cu rves of the type of 6 5 an d 1 8 suffi ce to determine the first
resonance potential and the interval between the second ionization
and first resonance Curves of the type 54 and 3 1 give the interval
b etween the two ionization points Curves of these two types
combined give the fir st r e s onac e potential and the two ionization
potentials without any use of the m e th od of applying initial poten
tial corrections of one curve to applied potentia ls in another
O ur final results were obtained in this manner A few values of
the interval first resonance fir s t ionization from curves of the
type of 3 0 check the value obtained by the other meth od within
experimental error The value of the second resonance potential
is based on fewer obser vations and is sub!ect to some doubt The
existence of a Second resonance point is however clearly shown
in the results o f H or ton and Davies
Table 6 gives the measurements o f critical potentials from 7 1
curves The note at the bottom gives the key to the identity
o f the five di fferent points o f infl ection obser ved
O ur results
are as follows :
V lt
0
3
.
.
.
,
.
.
.
.
.
.
.
—
,
,
.
,
,
.
.
.
s
o
Firs t
Fir s t
po te nt ial
ioniz at ion p ot e nt ial
S e c ond r esonanc e p ote nt ial
r e sonanc e
5
1 0.
13
,
abo u t
12
.
.
1 6.
Bohr s theory gives :
3 !;
5
2
51 i
5
’
V lt
o
10
Ioni z ation p otenti al of H1
Ioni z ation p ote ntial of H2
.
s
1
6
54
16 26
13
.
.
The conclusion that we have observed the resonance potentials
an d ionization potentials of both H an d H is fair ly eyid ent
The question arises as to whether or not hydrogen is dissociate d
w ithout being ionized by electron impact The energy required
volts on Bohr s
is equal to that o f an electron falling through
theory or
volts from Langmuir s value o f the heat o f dissocia
No c ertain evidence of inelasti c impact in this low range
t ion
.
2
1
.
’
’
.
I oniz a tion
a
nd
R es ona nc e P otentia ls
6 89
voltage was found though the possible existence of a non
selective stopping of low voltage electrons is app ar ent in some
of the curves Certa inly however there is dissociation of hydr o
gen by the catalytic action of the hot cathode (platinum palla
d iu m or tu ngsten)
A consequence o f the Bohr mo del for the hydrogen molecule is
that the d iff erence betw een the ionization potentials of the mole
cule an d atom is the work require d to d issoc iate hy drogen into
its atoms
O ur observed diff erence between ionization potentials gives :
of
,
.
,
,
21
,
.
,
.
L angm u ir
from h e at
5 v al u e
’
of
di ssoc iation
3 9
.
better check on the theory is obtaine d from the interval
first resonance potential to secon d ionization potential as this
interval is the most accurate one given by our observations being
base d on m easurements of 3 4 curves showing both points sharply
A
,
,
.
R i per im e nt al
v al u e
l
.
6
.
I I
i
O
.
2
values obtaine d by o ther observers for these in tervals give
r esults that are likew ise close to the values predi cte d by Bohr
Thus Horton and Davies get 2 5 volts difference b et ween io nization
p oints and
volts between first resonan
ce an d second ionization
Frank K nipping an d K ruger observe ionization at the first c r itieal
p otential but assuming that the ionization is a seco ndar yeff ect
occurring at the first resonance p otential their resul ts give an
:
interval of
volts which is within their exp erimental error
in agreement w ith the
volts predicted by theor y Th e interval
observe d by Davis an d Goucher of
volts is not very close but
there is evi dence that their metho d of corr ec ting for initial potential
is sub!ec t to error As t h e Bo hr D eb eye mo d el of the hy dro gen
molec ul e is tar from being an accepte d theory this close agreement
be tween the experimental an d predi cted V alue for the ioni zation
potential is an unexpecte d resul t Certainly the interval bet ween
io ni zation potential s is less than the work of di ssociation as
vo lts Frank K nipping
de rived from Langmuir s results viz
an d K ruger identify thi s work w ith the interval between their
observe d resonance point at
an d ionization at
but there
is no theoretical basis that w e c a n s ee for this de duction
h
T e
.
‘
.
.
,
,
,
'
:
'
‘
,
,
,
.
,
-
.
l
,
.
,
’
,
,
.
.
,
.
i
l
Scientific
6 90
f
P a p er s
o
the
Bu r ea u of S ta nd ar d s
[ V ol
.
16
Bohr has not predicte d the interval between resonance poten
tia ls b u t experimental evidence shows that it is about the same
as the interval betw een ionization potentials I f this were true
the secon d resonanc e potential shoul d be at 1
volts P ossibly
the assumption that the ratio of resonance potentials equals the
rati o of ionization potentials is more in ac c ord w ith theory This
woul d give 1
volts for the secon d resonance with a n interva l
between resonance potentials of 2 volts The experimental data
on this interval are inaccurate but range aro und the t wo values
and
Thus Horton and Davies observe the interval b e
tween resonance potentials as
volts ; Davis an d Goucher
volts ; Frank K nip p ing and K ruger
volts ; an d our result is
volts
The interval second resonance secon d ionization would on
this interpretation be
or
volts The inter val as observe d
by Frank et al is
volts ; by Horton and Davies 3 ; by us
This rather detailed consideration shows that the results of
various o b servers w hen properly interprete d are not disc ordant
beyond experimental error e xcept on one point viz the natur e
of the first critical potential Assuming that this is in eac h case
the first resonance potential an d that the ionization observe d by
some is a sec ondary e ff ect the resul ts of all observers agree w ithin
the probable experimental erro r w ith the Bohr theo ry of what
wo u l d be observed in a mixture of H an d H 2: The experimental
differences may seem large but the overlapping of e ffe c ts due
to the sec on d resonance and first ionization is a serious d ifficulty
in the radi ation metho ds of measurement The value of the
interval first resonanc e to secon d ionization is the bes t c hec k of
the theory with our method of measurement
,
.
,
.
.
,
.
,
,
.
—
,
,
.
.
,
,
,
,
.
,
1
,
.
.
VI
.
C O NC L U SI O N
Table 7 g ive s a summary of the c ritic al potentials of the s ix
elements stu die d in this paper together w ith the relate d spec tra l
l ines an d limiting w ave l engths The w ave lengths in italic s ar e
c ompute d from obser ve d potentials
Except in g the case of hydrogen these e lements al l Show a reso
n ance and ioniz at i on potentia l Similar in relat ive m agn itude to
those ob serve d in metalli c vapors Except for the cases of io d ine
and s u l phur the ac tua l m agnitud es of the potentials are l arger than
the potent ials ob serve d in any of the meta ls I n the case of sul
phur there is evidence that there are two resonance potentials an d
.
.
.
.
Scientific
69 2
P a p er s
f
o
the
B u r ea u of S ta nd ar d s
[ Vol
'
.
16
is readily dissociated by the hot w ire at the t emperatures em
ployed some monatomic vapor must be present especially s o on
the basis of the above high ly speculative theory The number of
e lectrons leaving the hot wire in a few seconds is comparable to
the total number of atoms of iodine present so that if this electron
a fli nit y existe d a large po rtion of the io d ine might readily consist
This condition is analogous to that
of negatively charged atoms
obtained with a metallic vapor above the ionization potential I n
this latter case the number of electrons leaving the c athode with
velocity sufficient to i onize greatly exceeds any m e as u r eab le ionic
current even when the mean free path of an e lectron i s such that
every e lectron pro duces ionization because of recombination as
evi dence d by the increase d pro duction of radiation Hence it
may be possib le that the observed resonance potential of iodine
and other nonmetallic vapors refers to the negatively charged atom
rather than to the neutral atom or molecule In the case of ioni
z a t ion positive iodine atoms or molecu l es are found as shown by
the downward bend in the c u rves illustrated Hence if negative
atoms are present in preponderance the ionization potentia l must
be the work necessary to e!ect at least two elec trons from the
iodine ion
The existence of the observed high initia l potentials on the ab ove
hypothesis may be due to the formation of a l ayer of neutral
iodine atoms on the inner net attracted to the net by the ir e lectron
affi nity
Were it not for the well established experimental facts in regar d
to the electron afli nity of these nonmetallic vapors we wou ld b e
l ikely to conclude from our work that the behavior of these vapors
is quite Similar to that o f metallic vapors and accordingly migh t
“
question the existence of a negative ionization potentia l
C en
t a m the general type o f curves obtained with nonmetallic vapors
is not mater ially di fferent from that for the m etallic vapors b u t
as stated above this might still be the case even though w e are
concerned with negative ions instead of neutr al atoms
The question as to whether the critical potentials ar e atomic or
molecular properties is an important point Hydrogen with its
two resonance and ionizati on potentials is appar antly unique
The cu rves are best explained as due to a m ixture at least near
the cathode of H and H in proportions varying with ex per i
menta l conditions N itrog en is certainly much less dissociated
than hydr ogen under simi l ar conditions s o it would seem that the
,
,
.
,
.
.
.
,
,
,
,
.
.
,
.
,
,
.
,
.
-
.
!
.
,
.
.
.
,
.
1
gig
I oniz a tion
"
a nd
R es ona nce P otentia ls
693
Sing le resonance and ionization potentials observed for it must be
ascribed t o N molecules H owever the resonance potential cor
responds to a frequency of the line emission spectrum and not of
the band spectra We must then admit that line spectra can be
emitted by molecules which is contrary to the general ly accepted
view that polyatomic molecules give rise to band spectr a only
O xygen is probab ly similar to nitrogen in this respect The
ionization point for the vapors may refer to the condition of the
vapor which exists predominantly 1n the tube i e molecules
neutral atoms or negatively charged atoms or if all con d itions
are present it is most like ly the lowest ionization potential for
the thr ee states accordingly for the neutr al atom if the theory of
negative ionization potential is true
Defin ite conclusions require further exper imenta l work in other
dir ections The stu dy o f the vapors from the spec tr osc 0 pic stand
m
oint
s
i
ilar
to
the
work
carrie
d
out
with
c
sium
ers
the
a
e
ff
o
p
most promis ing field The sing le line spectra are in spectral r e
gions favorable for obser vation and the physica l conditions for
dissociation of the molecules are obtainable in the laboratory
2
.
,
O
.
,
.
.
.
,
,
,
,
,
,
,
.
.
25
,
,
-
.
,
.
WASH I N ! TO N M ay
,
25
F oo
2
t
9
,
e a nd
1
2
0
9
.
M e g g er s B
,
.
S S ci P p r
.
.
a
e s
No
.
3 86 .
Scientific
694
TAB L E
C
urv
Re
e
1
—
P a p er s
Re s onanc e and
mar k s
T
33 3
"
f
o
the
B u r ea u of S ta nd a r d s
Ioniz ation P otential s
n nc
At re s o
a
of
P h os ph oru s
ml
paten
e
n
At io
[ VO L 1 6
ggfigh
p
i
zation
b—
1
3
ele
ctrode s
28
2
3
4 el e
ctrodes
,
ye ll ow
P
a
1. 0
48
.
13 4
.
28
z 3
25
3 5
9 5
25
3 4
9 2
5 8
2 4
25
3 4
9 4
6. 0
2 4
.
.
.
.
.
.
.
.
.
.
12. 8
25
7 z
25
.
5 8
.
3 3
10
.
12 9
10
10
do
14
ll
do
14
12
do
19
.
19
19
15
do
19
l6
do
27
6. 0
27
25
25
25
21
do
25
22
do
35
23
do
24
do
75
25
do
75
26
Red
28
29
R ed
P
380
do
420
and
ye llow
P
.
15
l3 3
15
24
.
3.0
8 8
.
5 8
.
2 8
.
13 6
24
.
3. 0
31
31
35
do
19 5
2 8
.
8 5
.
5 7
.
3. 0
13 S
19 5
.
420
2 8
8 5
5 7
3. 0
380
3. 0
8 8
5 8
2 8
3. O
8 8
5 8
!. 8
3. 0
9. 0
6. 0
2 8
.
.
.
.
.
.
.
.
200
42
do
130
130
.
$3 51
4
I o niz a ti o n
T AB L E 2
.
—
d R es ona nce P otentia ls
an
R e s onanc e
and
Io niz ation P o t entials
Applied potenti ls
a
R emar k s
C u rve
per
At on n
r es
a
to r e
a
ce
Iod ine
es n nce
potenti l
R
T em
of
o a
a
p ttienl
o
a
1
°
Method 1
C
10
10
10
d0
'
7
10
10
10
9 64
.
15
15
10
.
10 44
.
10
do
1o
9 94
.
14
12
13
14
do
M ethod 2
M eth d 1
do
do
17
18
19
20
21
22
10 64
.
24
10
o
15
16
14
.
11
.
11
ethod 2
do
M e th d 1
do
do
do
M
14
14
. .
10 54
.
o
o
. .
0
. .
5
. .
5
S
23
25
.
26
.
M
10
do
do
ean t esonance
20
20
pote ti l
n a
2 34*
vo lts
.
S c ien tific P a per s
696
TAB L E 3
Res onance
—
.
f
o
and
the B u rea u
n
d
S
t
a
a
r
d
s
f
o
Ioniz ati on P o te nti als
of
( Vol
.
16
S u l ph ur
Applied po tenti l s
a
R
C u r ve
em k s
T
ar
23 3
"
pote ti l
n
At re son nce
a
iti l Io iz tion
pote ti l potent i l
a
In
At ioni
n a
a
n a
a
zation
b—
°
M etho d 1
1
a
C
11 5
128
.
128
9 3
136
8 8
.
.
11 0
13 6
.
140
11 4
140
.
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
169
169
1 36
do
do
do
do
do
10
ll
12
13
14
1 36
17
18
19
20
21
22
140
26
27
do
31
o
o
o
o
o
o
o
o
o
o
o
o
o
o
o
o
o
1 1. 5
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
11 S
o
o
o
o
o
o
o
o
o
o
o
o
o
o
o
o
o
o
o
o
11 0
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
o
8 4
.
.
149
8 2
1 71
8 0
.
.
171
140
8 4
142
8 4
16 1
8 6
161
8 8
.
.
.
.
1 53
.
1 53
120
.
a
120
8 0
120
9 6
.
.
120
M e n reson nce potenti l
a
o
o
.
13 1
M ethod 2
30
o
o
13 1
do
do
do
25
o
o
8 0
142
do
24
o
142
do
do
do
do
do
do
do
16
.
136
do
15
80
a
140
9 0
140
9 0
.
.
lt
vo s .
o
o
o
o
o
I o niz a ti o n
TAB L E 4
.
—
a nd
R e sonance
R e s o na nce P o tentia ls
and
Ioniz ation P o tentials for Nitr ogen
mgfigfi
App lied potenti ls
R
p
a
M eth
E
ff
od
At
e
reson ce
an
I n
zation
n
mi u s
n
ce
pote
an
At
io iz
tion
n
8
oi
e
n
tia ls
a
mm
84
.
\
U
1
3
5
L e rd
Le rd
!
8 4
.
15 5
na
N
8 0
.
N
na
O
N
O
N
O
N
17 0
.
8 5
I
O
7 8
K
.
HN
I
'
9 0
.
HN
O
HU
I
9 0
.
I
HU
I
O
17
L e rd
na
.
O
H
O
H
17 0
.
H
16 6
o
H
16 9
23
.
.
.
HA
8 4
Q
8 3
(
21
8 0
.
.
N
Le rd
T ot l
N
na
7 5
N
H
a
H
7 0
.
H
26
H
N
7 5
.
n!
29
T
o0
ot l
w
0
1
a
\!
OU
:
m
n
a
o
m
o
M e n reson nce potenti l
M e n i niz tion potent i l
a
a
a
o
a
a
a
m
.
85
.
85
o
.
85
m
i
vo lts
.
16 .9 i 0.5
vo lts
.
S c ientific P a pers
69 8
—
Re sonanc e
L
E
5
TAB
.
f
o
and
a
n
d
t
a
r
d
s
S
f
the B u re a u
o
sm i
‘e
a
urv e
M eth d
P res “
sure
o
At
reson nce
a
b—
a
b
a
7 8
2
7 4
15 4
80
7 2
15 0
7 8
3
7
Le rd
na
.
45
.
45
.
45
6 6
14 8
8 2
5
6 4
14 6
8 2
5
6 7
14 8
8 1
5
2
13
2
6 8
14
2
6 7
22 4
7 9
6 0
22 0
80
15
16
17
Le rd
Le rd
na
.
25
.
25
18
6
19
6
20
6
21
6
22
9
23
9
24
9
25
9
26
1 2
27
1 2
28
29
30
31
L e rd
Le rd
na
35
14 2
80
14 2
80
14 2
6 4
14 5
7 9
14 S
6 6
7 8
14 4
14 2
6 8
14 6
7 8
13 S
6 6
8 0
14 6
l3 8
M e n res n nce pot enti
o a
7 8
35
.
na
a
80
2
na
a
l
16
oi
mi
reso
I n
z ation
nus
nance
poten
tials
c
2
2
.
Ioniz ation P o tentials for O x ygen
Applied pot ent i ls
C
[ Vol
olts
v
.
S c ientific P apers
0
0
7
TAB L E 6
-Re
‘
.
f
o
I oni z ation P o tent ials
of
Applie d potenti l s t critic l points
P
sonance
and
a
re
M
Cu v
ethod
a
n
d
d
r
s
t
a
S
f
the B u re au
o
a
a
c
Hyd rogen
[ VO L 1 6
C onti nu e d
—
ote ti l d iffere ce critic l po i ts
n
of
n
a
d
d—
n
a
a
54
55
10 5
56
1
57
L e rd
58
1
59
1
60
1
16 8
10 5
na
61
10 5
62
63
1
l6 5
10 2
65
17 5
66
10 5
L
9 6
1
10 5
67
68
69
10 5
70
1
71
re son nce
ioniz tion
nd i oniz t i o n
t re son nce rep e te d
successive collisio s f fi rst re so nce nd s eco d re son nce typ e
nd i oniz tion pot e ti l mi u s fi r st re so n nce po te ti l g i i g s econd i oniz t ion pot enti
volts
nd i oni z ti on po te nti l minu s fi s t i o iz ti o po tenti l gi v i g fi rs t i o i z t ion pot ent i l
volts
t re so n nce pot e ti l 10 40i 0 5 vo lt s
nd re son nce potent i l
volt s
ce po te ti l g iving fi rs t io i z tion potent i l
t i o i z tio p te ti l m inu s fi rs t re so
volts
=F irs t
b =F ir s t
a
a
a
=S eco
c
d = F irs
d 1=N
c— a
c—
.
.
a
.
a
a
.
n
o
=S eco
na
o
n
n a
a
n
a
a
n
a
.
vn
a
a
a
l
.
b=S eco
a
a
n
r
n
a
n
a
n
a
n
a
a
.
d—
(1 1—
b—
=F irs
a=S eco
a=F ir s
a
n a
a
a
n
.
.
a
a
n
.
T AB L E 7
—
.
n
nan
n a
o
S u m m ary of C r iti cal P ot enti als
R
E
a
leme t
n
O b
eso
s erv ed
of
T h eo
Vapor s
o iz tio
I n
!
r etica l
ave
le gth
n
.
O b
serv ed
A
a
T h eo
r etica l
n
!
ave
le gth
n
A in A
2 13 0
13 3
92 8
53 00
10 1
1220
2580
12 2
1010
.
.
.
73 0
0
n
and
ce
4 78
itroge
s s
a e
nan
A in
N
!
a
1 494 8
.
156 0
7 91
.
10 40
1S 5
796
13 3
9 11 78
.
.
.
.
16 5
.
t liciz e d w ve l ength s compute d f m ob serve d po te ti l s
[ mm wh ich th e o retic l pote nti l s h e b ee n c om p te d
I
a
a
n a
ro
ar e
a
a
av
u
.
5
.
.
Th e
other s
ar e S pe ctr os c0pic
v lue s
a