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 ! . . S S TANDARD S OF TRA TTO N D , I R EC T O R 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 . . , , B u r eau f S tandar ds o O CT O B ER 14, 1 9 20 NT S P RI C E, 5 C E 3 « :4 ? V 7 c t ’ , h e S u p er int end ent ! -uh of as D o cum nt h in t n g o e , D . s, C ! o v rnm nt Printin e e . —n ~ N! TO N ! O V ER N M EN T P RIN TIN ! ! A S HI 1920 I O FF C E ‘ 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 . . 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 . . 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 , , , , , , . , , , 1 . - . , , r . , r ran ck u P hy h 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 1 F ., . , . , an d , . , . , . , , . . . S P h S S n . . . . . . . , , , n . , . , Ph S P v . . , . . , . . . , . . . . . , . , . , , , . h P Ph S P , h . , . . . . . . . . , , . . ., . . . . , . 669 P , . 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 r . . . ! . , , . . . . , , , . . . - z . — , , . , - . , , . . F ’ r n ck a and H ertz , P hy s. ! it e . , 1 7 , p 40 9 , . 1 91 6 . 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 ' ' . . . ' , . , . — . I . . . , , 2 . , . I . , , , 2 , . . 2 I “ , I . , ‘ . - , . . 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 . . 2 . . ( ) 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 . . I I . , 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 , 2 , I , . . — . . l . ' 2 2 3 . . I 3 - ' 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 , . . 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 . . ' . , . ' , . 3 Ph ys . R ev . , 10, p . 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 . , . . , . . , . . ' . . — ! . — 8 . 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 . . . , , , , , , , , . . . . . , . , , , . . . , ° . 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 . ° , ' . . ° ° ‘ 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 , , . , . . . . 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 . . . , . , - . . ° ° , ° . , ° ° 4 , , , ° 2. . , . . . ' . . . . ur Jo . mr A e . C hm e . Soc . , 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 . . . . _ , - , 5 P hy s. R ev . , 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 “ . , . , , . 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
© Copyright 2024 Paperzz