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The infrared spectrum of HOCl
JOlIRN.\L
OF MOLECULAR
SPECTROSCOPY
The Infrared
23, 439-447 (1967)
Spectrum
of HOC1 t
The “I bands of HOC1 and DOCl have been examined ~~tlcr high resolution using a vacllum, grating infrared spectrometer. The following rot,atiotlal COILstants were determined. For HWCl: A” = 20.46 + 0.02 cm-‘, K” = 0.5058 f 0.0012 cm-‘, and C” = 0.4922 =t 0.0012 cm-‘; for HW’CI: A” = 20.46 k 0.0’9 cn-‘, and B” = 0.4902 & 0.0015 cm-‘; for DOCl: A” = 11.07 =t 0.04 cn--1. The geometry of the HOC1 molecule was found to be ,(()I%) == 0.97, i 0.01 w, 1,(0Cl) = 1.689 f 0.006 d and LHOCI = 104”47’ f 5”. INTRODUCTION
The lit#erature contains only one reference to a spectroscopic examinntic)tI of the HOC’1 molecule in the gas phase. Hedherg and Badger (2 j were able to make vibrational assignments, and carry out a force constant analysis, from low resolution infrared spectra of the HOC1 and DOCl molecules. They :dso tietermined (ilo - Bo) from the 2~1 band of HOC]. By assuming OH and OCI bond lengths they were able to estimate the L HOC1 angle at 113”. The present work is concerned with the high resolution infrared spectr:L of’ ~.hrt v1 bands of HOC1 and DOCl, and the molecular geometry derived from fhc ana.lysis of t.he fine structure. EXPERIMENTAL
HOC1 was prepared by placing a small amount of a slurry of mercuric oxidc and water in a l-meter absorption tube, quickly evacuating the tube, :uld admitting chlorine gas to approximately 20 cm of Hg pressure. In this mixture :u) equilibrium is apparentIy established according to HgO + Cl, * Cl,0
Hg + C&O,
+ H,O t-f 2HOCl.
Some Cl02 is also produced. Repeat’ed attempts to dry the gas mixture by passing it through :L tube c~f magnesium perchlorate only succeeded in completely removing the HOC1 t,oget,her with the HzO, and the HOCl/H,O concentration ratio appeared to rcwlnitl CtJIlStallt t,hroughout this drying process. t This work was carried out during the tenure of a National Post-Doctorate Fellowship, 1965-1966. 439
Research
Council
of C:LII:&
440
ASHBY 3463.25
cm-1
3447.25
I
cm-’
Ql
3?47.25 cm-’
3439.90
FIG. 1. The spectrum
of HOC1 between
cm-’
3464-3430 cm-’
DOCl was prepared by replacing Hz0 with D,O in the above preparation. Spectra of the ~1 bands of the HOC1 and DOCI molecules were taken on a a-meter vacuum infrared spectrometer: the spectral slit width being ~0.15 cm-‘. Near 3 p a 7200 lines/inch grating was used in its first order with a liquid nitrogen cooled PbS detector: near 3.7 ELa 1854 lines/inch ruled-echelle grating was used in its fifth order with a liquid nitrogen cooled InSb detector. Neon lines were used for calibration and, in the 3-l region, an interferometer was used to interpolate. DISCUSSION (a)
VI
OF RESULTS
: HOC1
A hybrid band, with its perpendicular component predominating, was found centered on 3609.2 cm-‘, 17 cm-’ lower than previously reported by Hedberg and Badger (1) . The rotational fine structure of the band was characteristic of an asymmetric top in the near prolate limit with A >> B N” C. It was not possible to use the band center for rotational constant evaluations because of sub-band overlapping, the presence of the two isotopic species H03%1 and H03’C1, and background water vapor absorption. The AK = + 1 transitions were also marred by water vapor absorption but were sufficiently clear for the evaluation of sub-band origins. The AK = - 1 transitions were relatively free of interfering water vapor absorption, and it was from these, mainly, that rotational constant’s were determined. The “QK and ‘Qx branches were single unresolved peaks (at least up to K = 7). Therefore, within the limits of accuracy of the measurements, the vibrational isotope effect was zero and the (A - B) constants for H03%1 and H03’C1 were
THE
INFRARED
SPECTRITM
OF HOC1
Table I R and P Branch Lines of HOC1 (cm -1 )
J
H035C1
H035Cl
HO%
H035Cl
HO%,
'24(J)
'n3(J)
Rd2( J)
RR1(J)c
'h&J&
3667.*996
3667.996
0 1
2 3739.642
3
3705.675
69.941
69.941
4
3772.591
40.641
5
73.603
41.584
07.623
71.896
71.896
6
74.566
42.553
08.626
72.782
73.030
7
75.542
8
76.508
9
77.493
10
78.453
73.709 3710.637 45.388
13.416
11 12
3780.378
13
81.377
14
82.290
15
3783.2M
48.412
78.231
16.393
3680.464
3750.241
17.395
79.934
81.443
51.323
18.408
3680.847
82.495
19.278
81.714
83.484
3720.134
b2.495
84.553
16 17
15.404
78.231
53.202
ta
54.145
83.384
85.654
19
55.101
84.334
86.633
20
56.050
85.042
21
56.993
85.816
22
3757.939
86.633
0
23
92.290
24 25
3690.147
3689.673
93.553
26
94.639
27
95.731
28
3696.802
ASHBY
442 Table
1 (continued)
Ho3*cl J
H035Cl
‘P2( JIG ‘P2( Jld
H035C1
HO37Cl
HO%1
HO37Cl
HO3%1
‘p,(J)
‘P,(J)
‘P4( J)
‘P4(
J)
‘P5( J)
0 1 2 3503.571
3545.664
3545.664
02.612
3459.141
5
43.715
43.508
01.598
58.179
6
42.699
42.582
00.608
57.151
12.492
I
41.766
41.542
3499.566
56.161
11.513
8
3540.840
3540.481
98.582
55.160
10.493
9
39.908
39.409
97.587
54.160
09.542
IO
38.932
30.333
96.498
53.159
08.530
11
38.020
37.220
95.591
52.189
07.507
12
37.og8
94.568
51.163
35.133
93.564
3450.157
3450.319
3 4
13
-
3413.489
06.504 05.509
14
35.274
33.989
92.542
3492.726
49.145
49.330
04.511
15
34.282
32.861
91.522
91.751
48.147
48.354
03.452
31.762
02.487
16
33.394
3490.529
go.766
17
32.487
3530.634
89.518
89.716
46.102
46.377
18
31.560
29.526
88.517
88.765
44.999
45.404
34o0.5a
19
3530.634
28.330
87.505
87.781
44.089
44.409
3399.491
20
29.747
27.208
86.496
86.764
43.078
43.350
98.465
26.053
85.498
85.749
42.089
42.314
97.429
41.073
41.470
96.486
3440.036
40.459
95.427
34.055
39.466
94.435
38.049
Y3.430
3393.434
37.038
37.440
21 22
28.015
24.870
84.479
84.762
23
27.208
23.778
83.433
83.789
24
26.232
22.551
82.369
82.763
25
25.396
21.278
81.421
26
24.624
20.120
27
23.778
3518.847
28 29
3480.809
-
3479.367
35.990
22.924
78.39
35.039
35.446
22.039
77.330
33.953
34.499
30
21.355
76.59
32.957
33.503
31
20.351
3475.466
31.968
3432.456
32
19.411
33
3518.403
01.489
3430.890
equal. The isotope effect of the chlorine atom was noticed only in transitions involving high values of J (see Fig. 1). The K numbering of the sub-bands was determined from the number of missing lines in the pP, branches with K = 3,4, and 5 (see Fig. 1).
THE
INFRARED
SPECTRUM TABLE
-I-l3
OF HOC1
II
RUIC-B.&NDORIGIKs AN;D COMHINATION DIFFERENCES FOR HOC1 h-
RQK
PQK
RQ~-~- pQ~+
1
(cm-l)
RQ~
-
'QK
0
1
3Gc6 .Ol
2 3
3701.71 3735.65 3767.62 3797.80
4 5
3548.64 3506.59 3463.13 3418.48 3372.68 3325.91
(i 7
159.42 238.58 317.19 394.94 471.89
153.Oi 229.06 3c4.49 379.34
frequencies J assignments R- and P-branch lines are given in Table I. Quadratic least squares fitt,ing of lines in RRK and ‘P, branches, according to Eqs. ( 1) and (2)) with K = 1, 2, 3, 4 for the RRK branches and K = 2, 3, 4, 5 for the pPI( branches, led to sub-band origins accurate to f0.02 cm-‘.
KRs(J)
= viUb+ [B’ + B” - D:k(2K” + LB’ -
V,(J)
=
viUb -
[l?’ +
+ [B’ -
Is” -
D&(2K
B”
D:k(2K’
-
B” + D:k(2K
+ 2K + l)](J + l)](J
+ 1)’
- 2K + l)]J - l)]J’
+ 1)
(‘1)
(21
where K = K” and it is assumed that D;, = D& . The positions of PQ6 , ‘Q; , and “QS were taken as the origins of their respective sub-bands and were accurate to ho.05 cm-‘. Table II gives the sub-band origins and the upper and lower state combination differences A$( K). Figure 2 shows a plot of A&‘( K)/4K versus (K2 + 1) for the ground and upper vibrational states. For a linear plot,, the intercept8 gives (A - B) and the slope, -20, , according to Eq. (3) :
Ad’(K)/‘4K
= (A - B) - 2D,(K” + 1).
(3)
Since the plot for the ground state is linear, the constants (A” - B”) = 19.96 f 0.02 cm-’ and D,” = (4.1 f 0.2) X 1O-3 cm-‘, are sufficient to describe the K dependence of the rotational energy levels. However, a similar plot for the excited state results in a curve. This curve can be transformed into a linear plot (the broken line in Fig. 2) when the term in HR’(Hg’ = -4 x low5 cm-‘) is subtracted from the ordinate. A comparison of the slopes of the two linear plots shows bhat (D R’ - DKN) is positive and equals ~2 X lo-” cm~‘. (;I - AN) = -0.77 f 0.04 cm-‘. The B and DJ, constants for H03’C1 were determined from quadratic least squares fitting of pPK lines, with K = 3, 4, .? according t’o Eq. (,2). The varia-
ASHBY
444
0
5
IO
15
20
(K’+l) FIG. 2.
Plots of A&‘(R)/4K
25
30
35
40
-
versus (IF + 1) for the HOC1 molecule
tion of the coefficient of J with K led to an estimate of D:k = -3 X low5 cm-‘. Thus B” can be determined by combjning the coefficients of J and J2 in Eq. (2) with the estimate of D:‘, . B” was found to be 0.4990 & 0.0008 cm-’ and (l?’ B”), -(4.5 f 0.5) X lOA cm-‘. The asymmetry of the molecule was seen in the profiles of the “&I , “Qo , ‘&I , and ‘Q2 branches. These profiles are in keeping with an (a’ - a’) transition of a molecule of C symmetry with I?’ E B” [Heraberg and Verma (s)]. As well, two series of ‘Pz( J) lines and two series of RR1(J) lines have been assigned for the H03’C1 molecule. The former reflect the asymmetry splitting of the energy levels with K = 1 in the upper vibrational state, and the latter, the asymmetry splitting for K = 1 in the ground state. The constants [B’ - ,1<(B” + 3C”)] and [I?’ - $i ( 3BN + C” )] were evaluated by least squares fitting of the two series of RR1(J) lines, according to Eqs. (4) and (5) : RR1(J),
= Gub + (B’ + SW”
+ 3C”))(J
+ 1)
+ (I?’ - x(B”
+ 3C”))(J
+ 1)”
= viUb+ (B’ + x/4(3@ + C”))(J
+ 1)
(4)
and
“Rl(J)d
+ (B’ - s(3~”
+ C”))(J
+ U2.
C.5)
THE
INFRARED
Constant
SPECTRLJM
3609.2 20.4ti
HOT1 f
0.5
f
0.02
Ii ”
0.5058
f
0.0012
(“’
0.4922
f
0.0012
p,
0.4990
rt 0.0008
11;, (4.1
HI;!) (.I' - -4j") ,B’ -
B”)
@IT’ - DK") (HK' - HKNi
-a
HOT1
1’1 .t ”
L)K”
OF HOC1
-c-4.5
It
-3
x
10-z
0.2)
x
10-s
-0.77 * 0.5) -2
f 0.o.l x lo-’ x 10-a
-4 x
10-j
x09.2 20.4fj
0.4902 (4.1
f
0.2, -0.77
f
0.5
I!Z 0.02
f
0.0015
x IO-” f
0.04
-2
x IO-3
-4
x
IOF
The constants so determined, when combined with the value of B”, led tjo B” = 030.58 f 0.0012 cm-’ and C” = 0.4922 f 0.0012 cm-‘. It is perhaps fort,uitous that, considering the errors in the A”, B”, and C”’ con&ants, the experimentally determined inertia defect, equal to 0.1 amu 8’, is in good agreement with that of 0.09 amu Ak’predicted by Oka and Merino (3 ). 8” for H03’C1 was estimated by plotting the difference between lines, of the H03’C1 and H03’C1 molecules, having the same J against J, for the K’ = 2 t k’” = 4 and K’ = 3 +- K” = 4 sub-bands. Assuming that t,he (B’ - 8” j and UyK constants are independent of t,he isotope, then the slopes of both plots should give (B” + B”JH~ss~~ minus (B’ + #1Ho~7~~ . The two slopes were 0.018 f 0.001 cm-’ and 0.017 f 0.001 cnl?, respectively. When combined with the known constants (B’ + B” ) for H03’C1, t#heseslopes result in B” = 0.4902 + 0.001.5 cm-’ for the H03’C1 molecule. A collection of all rotational constant,s determined for the HO”‘C1 and HO’“C1 ~nol~~ules is given in Table III. (b ) VI : DOC’I Because of the extensive D?O spectrum in the region of v1 of DOCl, only the Q branches of the perpendicular component could be measured. The D,O spectrum completely swamped the J rotational fine structure. K numbering of the Q branches was indicated by the loss of line-like character of the “Q1 , “Q. , ‘Q1 , and ‘Qz branches as compared t’o the “QK and ‘QK branches with K > 2. Again, the Q branches were unresolved, single peaks indicating that the vibrat,ional isotope effc>ct is negligible and that the (A - B) constants for D035C1 and D037C1 are equal. The frequencies of the branches, taken t)o be the origins of the sub-bands, are
446
ASHBY TABLE
IV
SIYWBAND ORIGINS,COMBINATION DIFFEREXCES, AND CONSTSNTs FOR DOCl (Cm-l)a J
RQK
PQK
SOME MOLECULAR
RQ~-~ - 'QK+I
RQ~- 'QK
2
2714.9
3 4
2734.3 2752.5
2Gll.G
126.0
122.7
2588.9
168.4
5 0 7 8
2769.8 278G.3
2565.9 2542.1 2518.4 2493.9
210.4 251.4 292.4
lci3.(j 203.9 244.2
-
a Y, = 2666.0 f 0.6, (d” - i?‘) = 10.60 + 0.03, Dg” 10.25 f 0.03, DK’ = (1.0zt 0.4) x 10-3.
= (1.5 + 0.4) x 10-3; (d’
-
P)
=
given in Table IV along with the upper and lower state combination differences. Also, the rotational constants determined from these differences are given. The band origin was calculated using these constants and its value of 2666.0 f 0.6 cm-’ is 8 cm-l lower than reported by Hedberg and Badger (1) . (c) MOLECULAR
STRUCTURE
The bond lengths and angle were calculated to fit the A” and B” constants of H03?J1 and A” of DOCl. They are r(OH) = 0.971 =t 0.02 8, ~(0Cl) = 1.689 f 0.006 A, and LHOCl = 104”47’ f 5”. In order to calculate A” for DOCl from the measured (A” - B”) constant a reasonable estimate of B” was assumed. Since t,he error in the choice could not be different from the actual B” constant by more than ho.01 cm-‘, A” could be estimated to a reasonable degree of accuracy and was placed at 11.07 f 0.04 -‘. It was found that the geometry gave rise to a calculated value of B” for ZCl which confirmed the choice. Also, the calculated value of B” for H03’C1 fell within the range of the experimentally determined value. The OCl bond length (1.689 f 0.0@6 A) is similar to those in C&O, 1.70 f 0.02 A (4)) and CH,OCl, 1.674 f 0.019 8 (5). However, the valence angle of 104”47’ f 5” is somewhat less than those of C&O, 110.8’ (4) and CH30C1, 112.8 i 2.1” (5). Perhaps these differences are due to steric hindrance between the CH, group and the Cl atom in the case of CH,OCl and electrostatic repukion between the two Cl atoms in the case of C&O. The angle is less than Badger and Hedberg’s (1) estimate of 113”. It should be mentioned that attempts were made to observe the microwave spectrum of HOC1 but they were unsuccessful. Apparently the HOC1 molecule decomposed too rapidly on the walls of the metal waveguide.
THE INFRARED
SPECTRUM
OF HOC1
447
The author wishes to thank Dr. A. E. Douglas for helpful discussion of the work embodied in this paper, and Dr. C. C. Costain for advice concerning the determination of molecuhtr structures from rotational constants. RECNVEU
: February
20, 1967 REFERENCES
I. K. HEDBEIIG AND R. M. BADGER, J. Che~e. Phys. 2. 3. 4. 5.
19, 508 (1951). G. HERZBERG AND R. VERMA, Can. .I. Phys. 42, 395 (1964). T. 01c.4 AND Y. MORINO, J. Mol. Spectry. 11, 349 (1963). J. I>. DUNITY AND K. HEDBERG, J. .11x. Chem. Sot. 72, 3018 (1950). J. S. RIGUEN AND S. S. BUTCHER, J. Chem. Phgs. 40, 2109 (1964).
OF MOLECULAR
SPECTROSCOPY
The Infrared
23, 439-447 (1967)
Spectrum
of HOC1 t
The “I bands of HOC1 and DOCl have been examined ~~tlcr high resolution using a vacllum, grating infrared spectrometer. The following rot,atiotlal COILstants were determined. For HWCl: A” = 20.46 + 0.02 cm-‘, K” = 0.5058 f 0.0012 cm-‘, and C” = 0.4922 =t 0.0012 cm-‘; for HW’CI: A” = 20.46 k 0.0’9 cn-‘, and B” = 0.4902 & 0.0015 cm-‘; for DOCl: A” = 11.07 =t 0.04 cn--1. The geometry of the HOC1 molecule was found to be ,(()I%) == 0.97, i 0.01 w, 1,(0Cl) = 1.689 f 0.006 d and LHOCI = 104”47’ f 5”. INTRODUCTION
The lit#erature contains only one reference to a spectroscopic examinntic)tI of the HOC’1 molecule in the gas phase. Hedherg and Badger (2 j were able to make vibrational assignments, and carry out a force constant analysis, from low resolution infrared spectra of the HOC1 and DOCl molecules. They :dso tietermined (ilo - Bo) from the 2~1 band of HOC]. By assuming OH and OCI bond lengths they were able to estimate the L HOC1 angle at 113”. The present work is concerned with the high resolution infrared spectr:L of’ ~.hrt v1 bands of HOC1 and DOCl, and the molecular geometry derived from fhc ana.lysis of t.he fine structure. EXPERIMENTAL
HOC1 was prepared by placing a small amount of a slurry of mercuric oxidc and water in a l-meter absorption tube, quickly evacuating the tube, :uld admitting chlorine gas to approximately 20 cm of Hg pressure. In this mixture :u) equilibrium is apparentIy established according to HgO + Cl, * Cl,0
Hg + C&O,
+ H,O t-f 2HOCl.
Some Cl02 is also produced. Repeat’ed attempts to dry the gas mixture by passing it through :L tube c~f magnesium perchlorate only succeeded in completely removing the HOC1 t,oget,her with the HzO, and the HOCl/H,O concentration ratio appeared to rcwlnitl CtJIlStallt t,hroughout this drying process. t This work was carried out during the tenure of a National Post-Doctorate Fellowship, 1965-1966. 439
Research
Council
of C:LII:&
440
ASHBY 3463.25
cm-1
3447.25
I
cm-’
Ql
3?47.25 cm-’
3439.90
FIG. 1. The spectrum
of HOC1 between
cm-’
3464-3430 cm-’
DOCl was prepared by replacing Hz0 with D,O in the above preparation. Spectra of the ~1 bands of the HOC1 and DOCI molecules were taken on a a-meter vacuum infrared spectrometer: the spectral slit width being ~0.15 cm-‘. Near 3 p a 7200 lines/inch grating was used in its first order with a liquid nitrogen cooled PbS detector: near 3.7 ELa 1854 lines/inch ruled-echelle grating was used in its fifth order with a liquid nitrogen cooled InSb detector. Neon lines were used for calibration and, in the 3-l region, an interferometer was used to interpolate. DISCUSSION (a)
VI
OF RESULTS
: HOC1
A hybrid band, with its perpendicular component predominating, was found centered on 3609.2 cm-‘, 17 cm-’ lower than previously reported by Hedberg and Badger (1) . The rotational fine structure of the band was characteristic of an asymmetric top in the near prolate limit with A >> B N” C. It was not possible to use the band center for rotational constant evaluations because of sub-band overlapping, the presence of the two isotopic species H03%1 and H03’C1, and background water vapor absorption. The AK = + 1 transitions were also marred by water vapor absorption but were sufficiently clear for the evaluation of sub-band origins. The AK = - 1 transitions were relatively free of interfering water vapor absorption, and it was from these, mainly, that rotational constant’s were determined. The “QK and ‘Qx branches were single unresolved peaks (at least up to K = 7). Therefore, within the limits of accuracy of the measurements, the vibrational isotope effect was zero and the (A - B) constants for H03%1 and H03’C1 were
THE
INFRARED
SPECTRITM
OF HOC1
Table I R and P Branch Lines of HOC1 (cm -1 )
J
H035C1
H035Cl
HO%
H035Cl
HO%,
'24(J)
'n3(J)
Rd2( J)
RR1(J)c
'h&J&
3667.*996
3667.996
0 1
2 3739.642
3
3705.675
69.941
69.941
4
3772.591
40.641
5
73.603
41.584
07.623
71.896
71.896
6
74.566
42.553
08.626
72.782
73.030
7
75.542
8
76.508
9
77.493
10
78.453
73.709 3710.637 45.388
13.416
11 12
3780.378
13
81.377
14
82.290
15
3783.2M
48.412
78.231
16.393
3680.464
3750.241
17.395
79.934
81.443
51.323
18.408
3680.847
82.495
19.278
81.714
83.484
3720.134
b2.495
84.553
16 17
15.404
78.231
53.202
ta
54.145
83.384
85.654
19
55.101
84.334
86.633
20
56.050
85.042
21
56.993
85.816
22
3757.939
86.633
0
23
92.290
24 25
3690.147
3689.673
93.553
26
94.639
27
95.731
28
3696.802
ASHBY
442 Table
1 (continued)
Ho3*cl J
H035Cl
‘P2( JIG ‘P2( Jld
H035C1
HO37Cl
HO%1
HO37Cl
HO3%1
‘p,(J)
‘P,(J)
‘P4( J)
‘P4(
J)
‘P5( J)
0 1 2 3503.571
3545.664
3545.664
02.612
3459.141
5
43.715
43.508
01.598
58.179
6
42.699
42.582
00.608
57.151
12.492
I
41.766
41.542
3499.566
56.161
11.513
8
3540.840
3540.481
98.582
55.160
10.493
9
39.908
39.409
97.587
54.160
09.542
IO
38.932
30.333
96.498
53.159
08.530
11
38.020
37.220
95.591
52.189
07.507
12
37.og8
94.568
51.163
35.133
93.564
3450.157
3450.319
3 4
13
-
3413.489
06.504 05.509
14
35.274
33.989
92.542
3492.726
49.145
49.330
04.511
15
34.282
32.861
91.522
91.751
48.147
48.354
03.452
31.762
02.487
16
33.394
3490.529
go.766
17
32.487
3530.634
89.518
89.716
46.102
46.377
18
31.560
29.526
88.517
88.765
44.999
45.404
34o0.5a
19
3530.634
28.330
87.505
87.781
44.089
44.409
3399.491
20
29.747
27.208
86.496
86.764
43.078
43.350
98.465
26.053
85.498
85.749
42.089
42.314
97.429
41.073
41.470
96.486
3440.036
40.459
95.427
34.055
39.466
94.435
38.049
Y3.430
3393.434
37.038
37.440
21 22
28.015
24.870
84.479
84.762
23
27.208
23.778
83.433
83.789
24
26.232
22.551
82.369
82.763
25
25.396
21.278
81.421
26
24.624
20.120
27
23.778
3518.847
28 29
3480.809
-
3479.367
35.990
22.924
78.39
35.039
35.446
22.039
77.330
33.953
34.499
30
21.355
76.59
32.957
33.503
31
20.351
3475.466
31.968
3432.456
32
19.411
33
3518.403
01.489
3430.890
equal. The isotope effect of the chlorine atom was noticed only in transitions involving high values of J (see Fig. 1). The K numbering of the sub-bands was determined from the number of missing lines in the pP, branches with K = 3,4, and 5 (see Fig. 1).
THE
INFRARED
SPECTRUM TABLE
-I-l3
OF HOC1
II
RUIC-B.&NDORIGIKs AN;D COMHINATION DIFFERENCES FOR HOC1 h-
RQK
PQK
RQ~-~- pQ~+
1
(cm-l)
RQ~
-
'QK
0
1
3Gc6 .Ol
2 3
3701.71 3735.65 3767.62 3797.80
4 5
3548.64 3506.59 3463.13 3418.48 3372.68 3325.91
(i 7
159.42 238.58 317.19 394.94 471.89
153.Oi 229.06 3c4.49 379.34
frequencies J assignments R- and P-branch lines are given in Table I. Quadratic least squares fitt,ing of lines in RRK and ‘P, branches, according to Eqs. ( 1) and (2)) with K = 1, 2, 3, 4 for the RRK branches and K = 2, 3, 4, 5 for the pPI( branches, led to sub-band origins accurate to f0.02 cm-‘.
KRs(J)
= viUb+ [B’ + B” - D:k(2K” + LB’ -
V,(J)
=
viUb -
[l?’ +
+ [B’ -
Is” -
D&(2K
B”
D:k(2K’
-
B” + D:k(2K
+ 2K + l)](J + l)](J
+ 1)’
- 2K + l)]J - l)]J’
+ 1)
(‘1)
(21
where K = K” and it is assumed that D;, = D& . The positions of PQ6 , ‘Q; , and “QS were taken as the origins of their respective sub-bands and were accurate to ho.05 cm-‘. Table II gives the sub-band origins and the upper and lower state combination differences A$( K). Figure 2 shows a plot of A&‘( K)/4K versus (K2 + 1) for the ground and upper vibrational states. For a linear plot,, the intercept8 gives (A - B) and the slope, -20, , according to Eq. (3) :
Ad’(K)/‘4K
= (A - B) - 2D,(K” + 1).
(3)
Since the plot for the ground state is linear, the constants (A” - B”) = 19.96 f 0.02 cm-’ and D,” = (4.1 f 0.2) X 1O-3 cm-‘, are sufficient to describe the K dependence of the rotational energy levels. However, a similar plot for the excited state results in a curve. This curve can be transformed into a linear plot (the broken line in Fig. 2) when the term in HR’(Hg’ = -4 x low5 cm-‘) is subtracted from the ordinate. A comparison of the slopes of the two linear plots shows bhat (D R’ - DKN) is positive and equals ~2 X lo-” cm~‘. (;I - AN) = -0.77 f 0.04 cm-‘. The B and DJ, constants for H03’C1 were determined from quadratic least squares fitting of pPK lines, with K = 3, 4, .? according t’o Eq. (,2). The varia-
ASHBY
444
0
5
IO
15
20
(K’+l) FIG. 2.
Plots of A&‘(R)/4K
25
30
35
40
-
versus (IF + 1) for the HOC1 molecule
tion of the coefficient of J with K led to an estimate of D:k = -3 X low5 cm-‘. Thus B” can be determined by combjning the coefficients of J and J2 in Eq. (2) with the estimate of D:‘, . B” was found to be 0.4990 & 0.0008 cm-’ and (l?’ B”), -(4.5 f 0.5) X lOA cm-‘. The asymmetry of the molecule was seen in the profiles of the “&I , “Qo , ‘&I , and ‘Q2 branches. These profiles are in keeping with an (a’ - a’) transition of a molecule of C symmetry with I?’ E B” [Heraberg and Verma (s)]. As well, two series of ‘Pz( J) lines and two series of RR1(J) lines have been assigned for the H03’C1 molecule. The former reflect the asymmetry splitting of the energy levels with K = 1 in the upper vibrational state, and the latter, the asymmetry splitting for K = 1 in the ground state. The constants [B’ - ,1<(B” + 3C”)] and [I?’ - $i ( 3BN + C” )] were evaluated by least squares fitting of the two series of RR1(J) lines, according to Eqs. (4) and (5) : RR1(J),
= Gub + (B’ + SW”
+ 3C”))(J
+ 1)
+ (I?’ - x(B”
+ 3C”))(J
+ 1)”
= viUb+ (B’ + x/4(3@ + C”))(J
+ 1)
(4)
and
“Rl(J)d
+ (B’ - s(3~”
+ C”))(J
+ U2.
C.5)
THE
INFRARED
Constant
SPECTRLJM
3609.2 20.4ti
HOT1 f
0.5
f
0.02
Ii ”
0.5058
f
0.0012
(“’
0.4922
f
0.0012
p,
0.4990
rt 0.0008
11;, (4.1
HI;!) (.I' - -4j") ,B’ -
B”)
@IT’ - DK") (HK' - HKNi
-a
HOT1
1’1 .t ”
L)K”
OF HOC1
-c-4.5
It
-3
x
10-z
0.2)
x
10-s
-0.77 * 0.5) -2
f 0.o.l x lo-’ x 10-a
-4 x
10-j
x09.2 20.4fj
0.4902 (4.1
f
0.2, -0.77
f
0.5
I!Z 0.02
f
0.0015
x IO-” f
0.04
-2
x IO-3
-4
x
IOF
The constants so determined, when combined with the value of B”, led tjo B” = 030.58 f 0.0012 cm-’ and C” = 0.4922 f 0.0012 cm-‘. It is perhaps fort,uitous that, considering the errors in the A”, B”, and C”’ con&ants, the experimentally determined inertia defect, equal to 0.1 amu 8’, is in good agreement with that of 0.09 amu Ak’predicted by Oka and Merino (3 ). 8” for H03’C1 was estimated by plotting the difference between lines, of the H03’C1 and H03’C1 molecules, having the same J against J, for the K’ = 2 t k’” = 4 and K’ = 3 +- K” = 4 sub-bands. Assuming that t,he (B’ - 8” j and UyK constants are independent of t,he isotope, then the slopes of both plots should give (B” + B”JH~ss~~ minus (B’ + #1Ho~7~~ . The two slopes were 0.018 f 0.001 cm-’ and 0.017 f 0.001 cnl?, respectively. When combined with the known constants (B’ + B” ) for H03’C1, t#heseslopes result in B” = 0.4902 + 0.001.5 cm-’ for the H03’C1 molecule. A collection of all rotational constant,s determined for the HO”‘C1 and HO’“C1 ~nol~~ules is given in Table III. (b ) VI : DOC’I Because of the extensive D?O spectrum in the region of v1 of DOCl, only the Q branches of the perpendicular component could be measured. The D,O spectrum completely swamped the J rotational fine structure. K numbering of the Q branches was indicated by the loss of line-like character of the “Q1 , “Q. , ‘Q1 , and ‘Qz branches as compared t’o the “QK and ‘QK branches with K > 2. Again, the Q branches were unresolved, single peaks indicating that the vibrat,ional isotope effc>ct is negligible and that the (A - B) constants for D035C1 and D037C1 are equal. The frequencies of the branches, taken t)o be the origins of the sub-bands, are
446
ASHBY TABLE
IV
SIYWBAND ORIGINS,COMBINATION DIFFEREXCES, AND CONSTSNTs FOR DOCl (Cm-l)a J
RQK
PQK
SOME MOLECULAR
RQ~-~ - 'QK+I
RQ~- 'QK
2
2714.9
3 4
2734.3 2752.5
2Gll.G
126.0
122.7
2588.9
168.4
5 0 7 8
2769.8 278G.3
2565.9 2542.1 2518.4 2493.9
210.4 251.4 292.4
lci3.(j 203.9 244.2
-
a Y, = 2666.0 f 0.6, (d” - i?‘) = 10.60 + 0.03, Dg” 10.25 f 0.03, DK’ = (1.0zt 0.4) x 10-3.
= (1.5 + 0.4) x 10-3; (d’
-
P)
=
given in Table IV along with the upper and lower state combination differences. Also, the rotational constants determined from these differences are given. The band origin was calculated using these constants and its value of 2666.0 f 0.6 cm-’ is 8 cm-l lower than reported by Hedberg and Badger (1) . (c) MOLECULAR
STRUCTURE
The bond lengths and angle were calculated to fit the A” and B” constants of H03?J1 and A” of DOCl. They are r(OH) = 0.971 =t 0.02 8, ~(0Cl) = 1.689 f 0.006 A, and LHOCl = 104”47’ f 5”. In order to calculate A” for DOCl from the measured (A” - B”) constant a reasonable estimate of B” was assumed. Since t,he error in the choice could not be different from the actual B” constant by more than ho.01 cm-‘, A” could be estimated to a reasonable degree of accuracy and was placed at 11.07 f 0.04 -‘. It was found that the geometry gave rise to a calculated value of B” for ZCl which confirmed the choice. Also, the calculated value of B” for H03’C1 fell within the range of the experimentally determined value. The OCl bond length (1.689 f 0.0@6 A) is similar to those in C&O, 1.70 f 0.02 A (4)) and CH,OCl, 1.674 f 0.019 8 (5). However, the valence angle of 104”47’ f 5” is somewhat less than those of C&O, 110.8’ (4) and CH30C1, 112.8 i 2.1” (5). Perhaps these differences are due to steric hindrance between the CH, group and the Cl atom in the case of CH,OCl and electrostatic repukion between the two Cl atoms in the case of C&O. The angle is less than Badger and Hedberg’s (1) estimate of 113”. It should be mentioned that attempts were made to observe the microwave spectrum of HOC1 but they were unsuccessful. Apparently the HOC1 molecule decomposed too rapidly on the walls of the metal waveguide.
THE INFRARED
SPECTRUM
OF HOC1
447
The author wishes to thank Dr. A. E. Douglas for helpful discussion of the work embodied in this paper, and Dr. C. C. Costain for advice concerning the determination of molecuhtr structures from rotational constants. RECNVEU
: February
20, 1967 REFERENCES
I. K. HEDBEIIG AND R. M. BADGER, J. Che~e. Phys. 2. 3. 4. 5.
19, 508 (1951). G. HERZBERG AND R. VERMA, Can. .I. Phys. 42, 395 (1964). T. 01c.4 AND Y. MORINO, J. Mol. Spectry. 11, 349 (1963). J. I>. DUNITY AND K. HEDBERG, J. .11x. Chem. Sot. 72, 3018 (1950). J. S. RIGUEN AND S. S. BUTCHER, J. Chem. Phgs. 40, 2109 (1964).