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Title
Rotation-Vibrational Spectrum and Structure of Methanol
Author(s)
Hamada, Keinosuke; Morishita, Hirofumi
Citation
長崎大学教育学部自然科学研究報告. vol.26, p.39-47; 1975
Issue Date
1975-02-28
URL
http://hdl.handle.net/10069/32853
Right
This document is downloaded at: 2017-06-17T16:30:11Z
http://naosite.lb.nagasaki-u.ac.jp
Sci.
Bull.
Fac.
Educ.
Nagasaki
UnivリNo.
26,
pp.
39-47(1975)
Rotation-Vibrational Spectrum and Structure
of Methanol
Keinosuke HAMADA and Hirofumi MORISHITA
Faculty of Education, Nagasaki University, Nagasaki 852
(Received October 31, 1974)
Abstract
The authors obtain the infrared rotation-vibrational spectrum of gaseous methanol
and the Raman spectrum of liquid one. Actually the infrared as well as the Raman
spectrum of methanol has been analyzed on the basis of CS symmetry.1,2) However,
the present observations show that the vibrational bands of methanol obtained can be
explained according to C3v selection rule, that is, it is in agreement with theoretical
expectations for C3v model that four parallel type bands are polarized in Raman and
have P, Q, and R branches in infrared, whose P-R separations are observed to be 40
cm-1 and estimated to be 43 cm-1 on the basis of the parameters for C3v model. In
addition, the obtained spectra of methanol resemble very closely those of acetonitrile,
whose symmetry is C3v 1)
I. Introduction
The symmetrical model C3v for methanol (H3COH) has eight fundamentals, four
totally symmetric ones (Ai) and four degenerate ones (E), all of which are both
infrared and Raman active, whereas less symmetric model Cs would give twelve
fundamentals(8A'+4A"), all of which are both infrared and Raman active. The
vibrational spectrum of H3COH has been assigned according to Cg model,卜6> but
this appears doubtful. Because only eight fundamental bands can be found in the
spectrum obtained, some Raman bands as fundamental are missing the corresponding
infrared ones and vice versa, and some inconsistencies in the fundamental assignments appear in the preceding literatures.
The authors have therefore found it worthwhile to reinvestigate the structure of
methanol by measuring the rotation-vibrational spectrum as well as the vibrational
one and by comparing the spectrum of methanol with those of structurally related
molecules.
__3. ik,, _ __ '_5__::_i : PrCN
Keinosuke HAMADA and Hirofumi MORISHITA
40
2. Experimental
The compounds are purchased from commercial sources and purificd by distillation.
The Raman spectrum is recorded on JEOL JRS-SIB spectrophotometer using argon
ion laser and the infrared spcctrum is measured with Shimadzu IR-450 spectrometer,
whosc gas cel] had a path length of 10 cm and KRS-5 windows.
/r
IR
f
O
'J
6
l il"
l¥ / r'i fl4
Wj t
･ ' L I [,
t L'T
l
.I ¥..
.lr$
vasCH3' 3075
I!!
Itl
llO mmHg
KRS-5
8asCH ' 1447
I
PCH 886
vsCH3' 2978 '
535
2x8asCH3 8sCH3' 1253
::
I 8sCH3' (P)
1237 ,vsC-I
(p) 522
vsCH3'(P)
2947
CH3JJ3040J_ ! I _ lL 8asCH3' 142.: 1!
Raman
,
prCH3
Ar+ :
l
l
4g80A
l
.
o
{:l}'A , r611 ¥
tl
IR
150 mmHg
KRS-5
l),{ ///
vasCH3' 3075
t ftI
8asCH3' 1417f /' r 3'
v6CH3' 2983 h
p CH 958 vsC-I
o
E:
8sCH3' 1309
2x&asCH3
'/
Raman
8sCH3' (p) 1298 1'sC-I
/
vsCH3' (P) 2959
Ar+ :
(,p) 596 1
SasCH3' 1433 /
pasCH3' 3050
).
4880A
i
l'
pCH3' 958 L
/1b 'L
/
/
, '
-1
3500 2500 2000 1500 lOOO 50O
O
3000
O
h¥/ i!jl(
IR
85 mmHg vasCH3' 3038 t
v3CH3' 2964
Il
O
Oj
¥
l ' ! JPT irr3 rIFlt'(
v5CN 2254
'
S i
1052 C-C
r 138O
Raman I sC-NJ/x8asCH3'1441
S (P:1373
CH3
a_CH3::::: (P) 2250 8 CH
vsCH3' (P) 2950
2x8asCH3
l rtv
vasCH 3030 f
4880A
2x8a5CH
.. J JprlC
J4
8asCH 1445
/i/_ _1'
prCN
vsC-C ( P)91 6
s
lb '
Ai
rhrl l._._ ¥
P CH '920 2xprCN 360
il
_ _ 38.0
_ _ d
J ._._ 2x;_CN
J¥U/.
$-J-J
IR' 70 mmHg. KRS-5
ILL, i"
¥¥ 2852 /
L"2x8asCH3 8asCH3' 1480 f I ,1
'
3710
O
(2993) l' t
PSOH
vasCH3 '
O
O
E:
prOH' 1347 l
v*C-O
v'CH3' (P)
r P'CH3'
1105
t! 1I2940
SsCH3'
(P) 1450
¥ j
2xsasCH3
vasCH3 2993 I
' ' a(p)
I 2835
n prCH3' 1114
Raman
l
Ar+ :
o
P OH
4880A p OH (P) 3330 1.L.__
'
.
s '
_-
3500
3000
(p) 103Q
l"l
v*C-O
/
_ _ _ _ _'-_'/
l--1 JH'J L-- J
4 ooo
1034
- vsCH3' 2940 8sCH3' 1452
I
/
'L
JJJH
2500
'
"
2000
-LLL:, t1 500
1000
/
J -J-'JLIJJ
500
Flg. I IR and Raman Spectra of H3CI, CH3Br H3CCN and H3COH
IR spectra are measured in gas state and Raman spectra, in liquid state
u. sing Ar+ Iaser 4880 A),
cm
to
-l
Rotation-Vibrational Spectrum and Structure of Methanol
4]
3. Results and Discussion
3-1. Vibrational spectra of acetonitrile(H3CCN)
From the fact that hydrogen cyanide(HCN) is linear it would appear very likely
that in H3CCN the C-C-N chain is lincar,1, 7) that is, that the molccule has a thrcc-
fold axis just as methyl iodide(H3CI) and mcthyl bromidc(H3CBr). Figure I shows
the Raman and infrared spectra of H3CI, H3CBr, H3CCN and H3COH. If H3CCN and
H3COH havc a three-fold axis of symmetry they would have, according to thc irrcducible rcpresentations shown in Table 1, four totally symmetric (A1) and four doubly
Table I Irreducible Representations of C3+ and C* for H3C-X-Y and C3+ for H3C-X
H3C-X-Y
H3C-X
C3v
4A*[R,p ; IR(lD] + 4E[Rdp IR(1)]
Cs
8A [Rp ; IR J + 4A,,[Rdp IR J
C3v
3A [Rp IR(li)] + 3E[Rdp ; IR(1)]
dcgenerate(E) vibrations, all of which arc both Raman and infrared activc. Eight
fundamental bands have indeed been observcd for H3CCN and H3COH in Raman and
infrared, rcspectively, as shown in Fig. I and Tablc 2. If the C-C-N or C-O-H chains
were not linear, there would be twclve bands, all of which arc both Raman and infrarcd
active. Thc agrecment of thc number of obscrved Raman and infrared fundamentals
with that cxpected on the C3. modcl is of coursc by no means a very strong
argument for this modcl ; but the following considerations support it further. As for
H3CI and H3CBr, onc would expect for H3CCN and H3COH a totally symmetric C-H
stretching vibration (v CH3) and a degenerate C-H stretching onc (v**CH3) and a
similar pair of CH3 symmetric dcformation(8*CH3) and CH3 asymmetric one(8asCH3).
These are indeed observed, with nearly the same frequencies as for H3CI and H3CBr
as shown in Fig. I and Table 2, where v*CH3 Iies around 2950; v* CH3, around 3000;
8*CH3, around 1000 and 8.*CH3, around 1450 cm 1 region as expected. For H3CCN
onc would further expect a C-N vibration(v*C-N) and C-C one(v C-C), which are
indeed observed at (p)2250 cm 1 in Raman and at ( Il)2254 cm 1 in infrared for
v C-N and at (p)916 cm 1 in Raman and ( ll)920 cm 1 in infrared for v*C-C. The
two remaining frequencies (dp)1040 and (dp)380 cm 1 in Raman which correspond
to ( )1052 and (1)360 cm 1 in infrared are apparently those of the two rcmaining
degenerato vibrations, a methyl rocking vibration(p*CH3) and CN rocking one (p*CN).
Thc totally symmetric vibrations of H3CCN give rise to parallel typc bands having
P, Q and R branches in infrared, and the degeneratc vibrations, perpendicular type
bands with succession of Q branches as shown in Figs. I and 2 .
These facts are strongly in favor of the C3. model for H3CCN as mentioned in
the refercncel) . The Raman and infrarcd spectra of H3COH seem to be same as thosc
of CH3CN cxcept having a symmetric O-H stretching(v.OH) and a O-H rocking
(p*OH) ban. ds instead of vsC-N and p*CN bands for H3CCN.
Table 2 Symmetry -Species, Selection Rules, Band Type P R Separation and Frequency Assrgnments of Skeletal Fundamentals
}
S pecies
of
Vibration
Raman
(1iq.)
IR
(gas)
v s X-Y
(p) 3330 3710
vsCH3
(p) 2940 (2940)
AI
¥AV
(p) I 033
Raman
PR
Ty pe obs. calc.
40
(lD
vsC-X
H3C-Br
H 3 C-C N
H3C-O-H
Form
(liq.)
IR r¥AvpR
(gas) Type obs.
(p) 2250 2254 1
24
(p)2950
24
.2964 i
([D
43
(p) 916
1034
Raman
calc.
(gas)
ni 1
nil
H3C-I
L¥AppR
nil
(p) 596
(gas)
ni 1
ni 1
Ty pe obs.
(p) 522
c alc .
ni 1
:
21
(lD
24 . 71
26
611
AVpR
IR
(1iq.)
( p)2947 2978
26
(ID
26 . 7
Raman
Ty pe obs. calc.
( p)2959 2983
24
920 '
IR
(1iq.)
;
535
(D
* :$
22 . 4
O
U,
:
21
r
(D
::
8.CH3
va sCH3
(p) 1450 1452
'
0
( p) 1373
2993 (2993)
(p)1298 1309
(1380)
3030 3038
(p) 1237 1253
26
3050 3075
>:
>
U
>
21
)
3040 3075
$
p+
::*.
8 a s CH3
1445
1475 1480
E
( i)
p.CH3
nil
1433 1417
l 44 1
(1)
nil
nil
( )
ni 1
1040 1052
1114 1105
1425 1447
958
nil
ni l
O
(1)
8821
nil
nil
886
958
t
380
1158 1347
360
ni 1
nn'
*il
t
*.
:
0 a
i
p * XY
F
ni 1
(1)
H
>
> E
2 x 8a =CH3
(p)2835 2852
( D
40
43
(p)2876 2876
( I)
?.
26 . 7
(p)2840 2856
()
26
24 . 7
(p) 2820 2845
()
( ) shows that the figure comes from that of Raman band, because it is not clear due to overlapping with another band.
?.
22 . 4
Rotation-Vibrational Spectrum and Structure of Methanol
parallel band ( Il)
8sCH3 ¥,sC-X
;scu3
43
Perpendicular band (J_ )
VsX-Y
vcn
as 3
6asCH3
Prcu3
PrXY
A¥,obs.= 21 au l
w
I I,r
f,
J
7
"
ni l
2978
12S3
S35 ,
nil
3075
1447
A¥,obs.= 26 an l
//
'*i
{
QI
(n
F:: .
nil
V
2983
l 309
61 l
nil
307s
l 417
958
A¥,obs.= 24 cm l
l
Z
U
111
l
over-
cn
, v r
r
(
v.
l apped
2964
1380
22s4
920
3038
1441
l052
360
A¥,ebs.= 40 arrl
::
r,
::'
overl apped
2940
J
..
/
1452 1034 3710
overlapped
2993
weak
*''"
ll05
1347
F,g. 2 The Band Shape of Infrared Parallel and Perpendicular Bands of CH31. CH3Br,
CH3CN and CH30H
3-2. Vibrational spectra of methanol(H3COH)
3-2-1 Parallel type bands"' ･･････The infrared band at 2845
cm 1 of
H 3 CI
might
44 Keinosuke HAMADA and Hirofumi MORISHITA
bc considcrcd as fundamcntal, but thc bands at 2845 and 2978 cm 1 form a doublet
duc to a Fermi rcsonancc8) whosc center coincidcs very nearly with twicc thc wave
number of the band at 1447 cm 1. Thcrefore thc 2845 cm 1 band of H3CI is not
fundamental one, but the 2978 cm 1 band corresponds to one fundamental only*1)
Thc band at 2852 cm 1 of H3COH that corresponds to 2845 cm 1 band of H3CI has
becn assigned to v*CH3 in ono of prcvious litcraturesl 6), but it should be assigncd
to tho first ovcrtonc of an asymmctric methyl dcformation (2x8* CH3), 'Nhich should
appcar in thc rcgion9) of 2800 cm 1. This ovcrtonc is usually found to be medium,
thercforc thc strong intensity of the overtonc for H3COH seems due to a strong
Fcrmi rcsonanco of 2 x 8**CH3 band with 2940 cm 1 fundamcntal onc. Tho 2940 cm 1
band can bo assigncd to v*CH3 Which is expccted to lie around 2950 cm 1 region,
to show P, Q and R cnvclopcs*2) in infrarcd and to bc polarizcd in Raman. Thc
strong Raman line and strong parallcl infrared at 1034 cm 1 obviously is thc C-O
vibration(v C-O) corrcsponding to v*C-C of H3CCN.
The two infrared bands at ( 11 )1452 and ( )1480 cm 1 which are corresponding
to the Raman bands at (p) 1450 and (dp)1475 cm 1, arc not well rcsolved, but arc
readily cxplaincd as corrcsponding to 8*CH3 and 8* CH3 of H3CCN, respectively. Thc O-H
strctching vibration corresponds obviously to thc infrarcd band ( Ii )3710 cm 1, which
has a frequcncy very similar to that of thc symmetrical O-H stretching vibration of
H20. Thc vcry considerable difference between the frequency (p)3330 cm 1 measured
in the Raman spectrum and that(3710 cm 1) measured in the infrared spcctrum is
duc to thc fact that thc Raman frequcncy rcfcrs to the liquid. The infrarcd spectrum
of thc liquidlo, 1 1) has shown thc v*OH band, just as does the Raman spectrum.
The frcqucncics of vCX(X=0,C,Br,1) and v XY(XY=0H,CN) should deeply decrcasc
in which tho frcqucncy changc in going from thc lightcr to thc heavier atom.
3-2-2 Perpendicu/ar type band･････････It is well known that thc frequcncics of
v**CH3 and 8* CH3 are remarkably constant throughout the scries of molecule H3CY
(Y=F,C1,Br,1) 12, 13). This is, also, thc casc for H3CXY(XY=0H,CN), Therefore the
depolarized Raman band at 2993 cm 1 of H3COH can bc assigned to vasCH3, which
shows the perpendicular type band in infrarcd. Thc 1475 cm 1 Raman band which
corresponds to the 1480 cm 1 band in infrarcd can casily bc assigned to 8**CH3 in a
similar manner as abovc.
Thc rocking vibration of a O-H group(p.OH) should givc a frcquoncy of thc sarnc
ordcr as thc bending vibration in H20(of course modified by thc different distribution
of masscs). It may bc identified both with thc depolarizcd Raman band at 1158 cm 1
*1) It is seen that the envelope of 2978 cm 1 band has P, Q and R branches in high resolution spectrum.
*2) The 2940 cm 1 infrared band does not show P, Q and R branches. This is due to overlapping of this band with the Q sequence of u.*CH3.
Rotation-Vibrational Spectrum and Structure of Methanol 45
and thc infrarcd band at 1347 cm i of pcrpcndicular typc. Thc largc diffcrcncc of
frequccics in p*OH bands bctwecn gascous infrarcd and liquid Raman spcctrum is duc
to strong hydrogcn bonding in liquid state, as docs v 0H. Thcrc remains thc rocking
vibration of CH3 group(p*CH3), accordingly thc infrarcd band at ll05 cm 1 must bc
assigncd to the p.CH3, whose corrcsponding Raman band is wcak onc at lll4 cm 1.
4. Band Contours
4-1. P-R separation･････････Thc parallel bar!_ds are those for which the electric moment
oscillatos along the symmetry axis, and thc cnvelopc of those bands possesses P, Q,
and R branchcs, whosc P-R separation, AVpR is expressed by Gerhard and Dcnissonl4)
as follows;
AVpR = S( p) 17tVh T/ IA
whcrc the separation function S(p) is given by the following cmpirical formula,
10g I oS(p) = O. 721/ (p+4) I ･ 1 3
whose parameter p is equal to (IB/IA)-1.
On the assumption that thc structure of H3COH is C3 having the followin r
parameters, O-H=0.96A, O-C=1.427A, C-H=1.lOA, tetrahedral HCH angle and COH
anglc of 180', thc authors cstimated the moment of inertia about top axis to bc
IA=5.09 x 10-40 g･cm2, and that about the axis perpend.icular to thc top axis to bc
IB = 32.13 x 10-40 g･cm2. Thus thc P-R separation of the parallel bands of H3COH
at 25 C is estimated to be 43 cm 1. The P-R separation for the bands, v*O-H,
v*C-O and 2 x 8**CH3 are obscrved to be 40 cm 1 in Fig. 2. Therefore, the agreement
is good and may be regarded as fairly satisfactory. The separation for v*CH3 can
not bc observed duc to overlapping*2), and that for 8 CH3 Can not be observcd due
to bc too weak. The obscrved and calculated P-R scparations for the parallcl bands of
H3CCN, H3CBr and H3CI arc shown in Table 2. Thc agrecmonts seem to be fairly
good.
4-2. Rotational fine structure････････- The rotational constant B is calculatcd to be
0.87 cm 1 from thc equationl5), 1 =hl87r2clB and IB=32.13xlO-40 g･cm2 calculated
previously. The constant
can, too, be obtained from the frequency separation between lines in P or/and R branches which is equal to 2B15). Fig. 3 shows that the
frequency separation in P branch of v.CO band is 1.88 cm 1. Thc agreement of the
observed value with that calculated on thc basis of C3, symmetry is regarded as
satisf actory.
4-3. Family of Q branches････････- Thc perpendicular type bands are thosc bands
for which the clcctric moment oscillates perpendicular to the figure axis, and which
consists of a t amily of Q branches in infrared and are dcpolarized in Raman. It is seen
in Figs. I and 2 that thc Q branchcs of thc porpcndicular bands oxihibit an intcnsity
altcrnation of thc typc strong, wcak, wcak ctc. Obscrvation of such an intcnsity
altcrnation in a Q branch conscquencc is sufficicnt to cstablish that thc rotating species
Keinosuke HAMADA and Hirofumi MORISHITA
46
l050 1000
lIOO
950
la'(pR = 40 cm l
R
Q
lOS4
l034
l014
I2B = 1.88 cxTL l
Fig. 5 Rotation-Vibrational Spectra of v.CO of CH30H
has C3 Symmetry about the axis of rotationl6).
5. Conclusion
The experimental results and the computations of P-R separation and constant B
are in excellent agreement with the theoretical expectations for C3 , model of methanol.
But the only argument against C3, model of H3COH is that the C-O-H chain in
H3COH should be bent, because the fact that the H20 molecule is bent suggests
strongly that the C-O-H chain is bent as well. However it is possible to consider the
2s and 2p, orbitals in oxygen atom as being hybridized to be linear -O-. In addition, some literatures support experimentally a linear -O- for gaseous Z-O-H(Z=
K,Rb,Cs) 1 7 2 o) and trifluorotrichlorodisiloxane(F3SiOSiC13) 2 l) .
Above all, it seems to be sufficient evidence to justify C3, model for methanol
that an intensity alternation in Q branch sequence of perpendicular typc bands is observ-
ed. However the final decision must await the results of the further study, because
some literaturesl 6, 22, 23) support C model for H3COH. Table 2 Iists tentative
assignments for the fundamental bands observed together with symmetry species and
selection rules.
Grateful appreciation is expressed for financial support of this work by the
Scicncc Rcsearch Fund of thc Ministry of Education.
Rotation-Vibrational Spectrum and Structure of Methanol 47
Ref erences
1)
G. Herzberg "Molecular Spectra and Molecular Structure 11 . Infrared and Raman Spectra
of Polyatomic Molecules" Van Nostrand Reinhold Co. New York(1945) p. 332, 334
2)
M. Falk and E. Whalley, J. Chem. Phys., 54, 1554(1961)
3)
J. O. Holford, L. C. Anderson and G. H. Kissin, J. Chem. Phys., 5, 927(1937)
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E. F. Barker and G. Bosschieter, J. Chem. Phys., 6, 563(1938)
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H. D. Noether, J. Chem. Phys., 10, 693(1942)
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A. W. Reitz and R. Skrabal, Monatshefe f. Chem., 70, 398(1937)
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A. Adel and E. F. Barker Phys. Rev., 45, 277(1934)
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M. G. Miles, J. H. Patterson, C. W. Hobbs, M. J. Hopper, J. Overend and R. S. Tobias,
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l O)
J. Errera and P. Mollet. Nature, 158, 882(1936)
1D
A. M. Busmell, V. Deitz and W. H. Rodebush, J. Chem. Phys., 5, 501(1937)
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W. H. Bennet and C. F. Meyer, Phys. Rev., 32, 888(1928)
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J. G. Moorhead. Phys. Rev., 39, 788(1932)
1 4)
S. L. Gerhard and D. M. Dennison, Phys, Rev., 43, 197(1933)
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G. M. Barrow "Introduction to Molecular Spectroscopy" McGraw Hill, N. Y. (1962), p. 52
16)
and p. 153
M. Davies "Infrared Spectroscopy and Molecular Structure" Elsevier Publishing Co. New
York (1963). p.153
17)
D. R. Lide, Jr. and R. L. Kuczkowski, J. Chem. Phys., 46, 4768(1967)
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C. Matsumura and D. R. Lide, Jr.. J. Chem. Phys., 50, 71(1969)
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D. R. Lide. Jr. and C. Matsumura, J. Chem. Phys., 50, 3080(1969)
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E. P. Pearson and M. B. Trueblood, J. Chem. Phys., 58, 826(1973)
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K. Hamada, J. Phys. Soc. Japan, 36, 617(1974)
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Y. Y. Kwan and D. M. Dennison, J. Mol. Spectrosc., 45, 291(1972)
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R. M. Lees, J. Chem. Phys., 57, 824, 2249(1972)