- Email: [email protected]
High resolution infrared spectrum of the ν1 band of 14N16O2
JOWNAL OF MOLECULARSPECTROSCOPY69,421-434
High Resolution Infrared MICHEL
(1978)
Spectrum of the
LAURIN
AND ALDEE
v1
Band of 14N160,
CABANA
Department de Chimie, Univers& de Skerbrooke, Sherbrooke, Quebec, Canada JlK
ZRl
The infrared spectrum of the ~1 band of i4Ni60z has been recorded with a resolution about 0.025 cm-i in the region extending from 1480 to 1270 cm-‘. From about 1350 cm-i, absorption became progressively weaker and no absorption at all could be detected below band origin located at 1319.797 cm-i. Because series with low values of K. could not measured, constants which depend strongly upon the molecular asymmetry could not determined.
of the the be be
INTRODUCTION The absorption spectra of two fundamental bands, YZ(I, 2) and ~3 (3, 4), as well as those of several overtone and combination bands (see ref. (I)) have already been obtained under high resolution. However, no high resolution data have yet been reported for the weak ~1 fundamental. In their classic study of the infrared spectrum of several bands of nitrogen dioxide, Arakawa and Nielsen (5) have pointed out that the symmetric stretching vibration VI presented the most serious difficulty with regard to experiment and analysis. Although the spectrometer available to these authors did not allow the resolution of the individual vibration-rotation lines, Arakawa and Nielsen have recognized that internal intensity anomalies were such that the band origin is located completely outside the region of absorption. This paper presents the high resolution infrared absorption spectrum of the ~1 band of NO2 and its analysis.
EXPERIMENTAL
DETAILS
The spectra were obtained with the 2.5-m vacuum spectrometer at the Universite de Sherbrooke (6), in the eighth and ninth order of the grating and calibrated with the 1 c 0 absorption frequencies of carbon monoxide as measured by Guelachvili (7). The region extending from 1480 to 1270 cm-’ has been scanned but no absorption has been found below 1320 cm-i. The scan to the high frequency side is not limited by the usual intensity falloff but rather by the fact that the y1 band runs into absorption by the P side of the much stronger v3 band. Absorption lines below 1335 cm-’ were very weak and their assignment remained uncertain. Therefore none of these could be included in the fit. The working resolution was about 0.025 to 0.030 cm-‘. Strong lines could be measured, in this region, with a precision of about 0.003 cm-’ or slightly better as indicated by the standard deviation of the fit (8) which was 0.83. 421 0022-2852/78/0693-0421$02.00/0 Copyright Q 1978 by Academic Prew. Inc. AU rights of reproduction in any form reserved.
422
LAURIN
*d.s
AND CABANA
d
0
l&o
FIG. 1. The ZQvibration-rotation band of 14N1BO* recorded at about 90°C with a spectral slit width of 0.025 to 0.030 cm-l and an absorption path of 16 m. The sample pressure was about 10 Torr from 1480 to 1376 cm-’ and about 35 Torr to the lower wavenumbers. The strong lines observed below 1350 cm-l do not belong to nitrogen dioxide.
The sample of NOz, obtained from Matheson of Canada Ltd., was found to contain appreciable quantities of CO2 and NO. These impurities were removed by condensing the gas at -79°C in a trap and pumping over the solid until it became white (I). A multiple path absorption cell was used and, since y1 is extremely weak, it was necessary to use long paths and relatively high sample pressures. Absorption by nitric acid and dinitrogen tetroxide, the former present as an impurity and the latter in equilibrium with NOz, has hampered us from using either very long path lengths or higher sample pressures which would have provided us with the desirable absorption at the lower frequencies. It is known (9,lO) that the v3 and vI bands of nitric
THE VI BAND OF “N’602
14oi.5
14oA.5
15d.O
1596.5
03:.5
1581.0
1401.0
,554.O "O,,; PO,i K.*4
14oLA.o
WA5
423
,,s:
5
l5d.5
Ins:*
IS7A.S
FIGURE1-Continued
acid absorb strongly in the region extending from 1370 to 1270 cm-‘. A simple calculation, using the data reported (IO), shows that, with an absorption path of 16 m, 0.03 to 0.04 Torr, HN03 would lead to complete absorption over the entire region specified above. A freshly purified sample of NO2 showed only weak absorption by nitric acid but in a matter of no more than a few hours absorption by HNOl became so intense that the sample had to be replaced. One of the strongest bands of dinitrogen tetroxide, VII, is centered around 1261 cm-l and from the data previously reported (II) it is estimated that with a path length of 16 m, 05Torr Nz04 would lead to complete absorption between 1320 and 1220 cm-‘. This has limited the sample pressure to 35 Torr since higher pressures would require higher temperatures which favor rapid formation of HNOa. We have used sample pressures in the range of 10 to 3.5 Torr, a path length of 16 m, and a temperature of 90°C. A compressed scan of the band is reproduced in Fig. 1.
424
LAURIN
AND CABANA
I
l36l.O
1364.0
13d.o
,33&o FIGURE
LINE ASSIGNMENT
l-Continued
AND INTENSITY
ANOMALIES
Line assignment in this band, like in any other B-type band of NOz, was complicated by the spin splitting, but the most serious complications arose from intensity anomalies which are greater in this band than in any other band of nitrogen dioxide. These anomalies may be briefly described as follows: on the low frequency side of the band origin no absorption line was intense enough to be measured, and on the high frequency side, absorption was very weak for the lowest values of K, but it increased progressively with increasing values of K until it blended with the much stronger absorption from v3. Furthermore lines which are expected strongest are weakest and vice versa. More explicitly, no PQK-, pPK-,and PR&ype transitions were found but only, transitions were in order of decreasing relative intensities, RP~-,RQK-, and a&-type observed. These unusual intensity perturbations are thus more severe in VI than in 2~1 (I) where, in turn, they are more severe than in 213 (II), but in no case does there appear
THE
~1 BAND
425
OF “N”Oz
134.0
131;.5 FIGURE I-Continued
to be any frequency perturbation. Figure 2 shows a selected portion of the spectrum which illustrates these anomalies. After several false starts a series of lines was assigned to transitions of the RP4 branch. This assignment was verified since line frequencies of the RQP series could be precisely predicted from these RP4 transitions and the accurately known ground state energies. After a certain number of lines had been assigned, these were used to obtain the frequency of the band origin, ~0, and the upper state rotational constant a’. These newly determined constants were used to extrapolate the line assignment further. All line
V
I
24 I
23 v 38
V
39
I
1406.5
V
25
v 40
V
26
27
V
41
v 42
2s P 43
I
1403.5
FIG. 2. Selected portion of the ~1 band illustrating the intensity anomalies and the spin splitting.
W
7
0 0 l 0 0 5 0 5 0 5 5
c
.”
W .Z
oc
*I’
.
. . . . . . . . . . . .
.
91
oc sz
zc
.
. .
.
oa
ZL
.a
ez
El .I b 9 . 0 9. . . t. 0. OF PC .I .I .I a!* .I . 5. I. 4s LC OS
. . . . . . . . * .
cc
.
.
.
.
B.? 92 :; 01 0, 9, .I II 0,
.PY
.
01 I, 61 Cl II
9
s
.z
6
PY
11
5 5 0 0 0 6 5 5 5 5 5 6 5 5 0 6 5
PO .I II 01 01 .I 10
a.?
5
6.
. .
. . . . . . . .
ci ,a
0, 91 .I 11 01 0 0 .
.
z .. . .
1
.
. . l . PC
.
1. 0.
.P
. .
oc
oc
.c
0. *. .P 91 SC 01
or
ON
EC
. .
La! SL
w
1s
5 . . . . . . . t . . . . . . . . . . .
I 318V.L
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
1
l
.
.
.
.
.
.
.
4
. . . .
OISLRVLD
-e..** -0.b.b. ..o.J7 0.00.. -0.00.. . . . . . 0....7 . ..O.. -....J. -.* 0.03 0...2* -0.0011 -0.0.5. -...,I, -0. ..s7 0.0.03
..a
-0.001. -0. ..a. . . ..I* -....JJ -....1. 0.003. . ...11 -0.003. -0.0077 . . ..U 0.003. 0.0.2, . . . -0.002. 4.002,
. ..a. -.....* ..-
..oon -....a. -...... . . ..I.
0.n.I -....,. . ..07. ~..01. -0.0011 -0.o.w -.....* -0.0U. -0.000. . . . .
-.....I
o-c . ...7.
TABLE I-Continwd
-
-
3. . .
.a
6
0
0
0
0
0
e
0
-
-
a. aa .7.
0 0 1. IP 1. I. ,.
.-
6 0
0
6 * -
-
s.
0
.
-
1. 3. 3P 3.
l . 0 0
.o.u ..nu
.
a*
73 I7
a
91
a.
0 (1 13 IS I7
..
.7 4.n.a 4.oa7 -...... 4.n.. -..m 4.n.7 -.a... 4rY.b 4.m -..-a 4.“PI 4d.m 4....b 4...m 4...4. 4d.b. . ..“7 . ..I.. -.a.., -...... 4.n.. -.....I -....J. 4.n.. -*...sa 4.m.. 4...s7 4d.n -...W. 4o.n. -0.o.n 4d.a. ..OII3 4.W. -.....J 4.nrs 4.a.. 4.o.m . . ..I. -...a. . . .
..owo
..a..
l .aaJ l .n.0
.3
.s
l
.a
3. 37 s7
O-C 04.7. ..Y
0
01
PI .I Ll
I.
.*
P
0. OP PC
K;
K;
TABLE I-Continued
I
-..oom
-0.00.3
0.0053 0.003s
O.OOL.
0.0003
-0.00,
L
O.COOS
-0.004,
‘0.0085
-0.00~0 -0.0*35 0.0005 -0 .oo.
-0.0120
0.0005 -0.0005 O.OO.?B 0.0005 -0.0026 -0.0091
-o.ooo*
0.0014
0.0022
0.0931
-0.0013
-0.0012 -0.OoOT
0.0221 0.0070
0.0092 O.OL61
o-c
TABLE I-Continued
THE ~1 BAND TABLE
OF 14N’60z II
Observed and Calculated Spin Splittings (cm-‘)
Transition
Ilvoba AYobs-Avc.lc
%,3 - 94,6 to.220 lO5.5 - 114.8
to.164
431
in the Ye Band of L4N1(02
Transition
Avobs Auob,-Avc,lt
-0.015
166,10 - 175,13 to.126
to.002
-0.001'
167.9 - 176,12 to.158
-0.008
125,7 - 134*10 to.141
-0.011
177,11 - 1B6*12 to.152
-0.003
145.9 - 154,12 to.123
-0.006
207,13 - 216,16 to.123
-0.007
165,11 - 174.14 to.108
-0.003
257,19 - 266,20 to.097
-0.003'
175,13 - 184,14 to.114
to.009
267,19- 276,22 +0.088
+0.008a
18 - 194,16 to.091 5.13
-0.006'
297,23 - 306,24 to.082
-0.002
195,15 - 204,16 to.090
-0.002
307,23- 316,26 to.069
-0.006
205,15 - 214*_
-0.006
130.6 - 147.7
to.230
t0.005.
215,17 - 224,18 to.066
-0.009'
158,8 - 167,9
to.198
-0.010
2$19
-0.007'
198.12 - 207,13 to.149
-0.010
265.21 - 274,24 to.062
-0.003
2211.14 - 23,,17 to.123
-0.012
275,23 - 204s24 to.059
-O.OOla
236,16- 247,17 to.113
+o.olsa
"5.23 - 294,26 to.048
-0.003
278,20 - 2137,21to.097
-0.010
295.25 - 304,26 +0.043
-0.010
268,20 - 297,23 to.092
-0.012.
-0.009
298.22 - 307,23 +o.ow
-O.O1oa
-0.002
30*,22 - 317,25 to.085
-0.011
+o.oOOa
318,24 - 327,25 to.083
-0.008
+o.on1
- 254,22 to.064
96.4 - lO5.5
to.249
136.8 - 145.9
to.153
156,10 - 165,11 to.132
assignments were verified by calculating the appropriate ground state combination differences. The frequencies of the observed lines used in the final fit together with those calculated using the final set of constants are reported in Table I. DATA
TREATMENT
The splitting produced by spin-rotation interaction is quite large in this B-type band. The measured splittings, given in Table II, were fit in the manner described previously using expressions which are good through the second order (I). The third term of those expressions, which is the only one determining (w, - e,,), arises because of the asymmetry of the molecule. It is usually invoked only for the K, = 1 levels. It had to be left out from the fit since no transitions involving such levels could be measured and therefore the value of (t W,- eec) could not be calculated for VI. The constants obtained from a least-squares fit, with the ground state E’Sand qaoaa fixed to the values reported (I), are given in Table III. These spin-rotation constants were then used to correct the average frequency obtained for a spin split line for the shift resulting from the asymmetry in the spin
432
LAURIN TABLE
Transition
CABANA
II-Cmtinued
TransitIon
AVobe
Avobs-Ay CdC
to.192
-0.014
356.30 - 365,31 to.053
-0.003
209,11- 21g,14 to.159
+o.o05a
366,30 - 375,33 to.048
-0.006.
Q3
-0.005
ll9.9
a
AND
- 18g,lo
"ohs
Avc,bs-Av ClllC
to.001
376,32 - 385,"
239.15 - 2'8,16 to.128
-o.oo3a
"6.34 - 405,35 to.039
-0.010
219,19 - 2a*,20 to.114
-0.008
ll7.5 - 126.6
to.242
-0.009
269.19 - 29*,22 to.104
-0.014
127.5 - 136.8
to.207
-0.021
- 226,14 to.146
to.046
2g9.21- 3og,22 to.102
-o.oloa
l'7*7 - 146.8
to.187
-0.020
"6.14 - 205,15
-0.009*
l57.9 - 166,10 to.161
-0.016
206,14 - 215,17 to.095
-0.012
'09,21 - 31g,24 to.093
-0.015
to.103
216,16 - 225,17 to.092
-0.009a
'19.23 - 328,24 to.089
-0.005
226.16 - 235,19 to.089
-0.006a
359,27 - 368,28 tO.060
-0.002
236,18 - 245,19 to.062
-O.OOla
389.29 - 398,32 to.079
-0.003'
'256,20- 265,21 to.079
to.006
l310.4 - 149,9
to.317
to.002
266 2. - 215 23 to.076 # 276,22 - 285;23 to.064
-0.003
1510.6 - 169,7
to.256
-0.007
2510,16-26g,17 to.143
-0.006'
-0.011
206,22- 295,25 to.073
to.001
3010 20- 319 23 to.116
-0.004
2g6,24 - 305,25 to.067
-0.003*
'%0:26- 379.29 to.089
-0.008
306,24 - 315,27 to.066
to.001
l
THESELINES WERE GIVEN A WEIGHT OF UNITY; ALL OTHERS WERE GIVEN A HEIGHT OF ONE QUARTER
splitting. The line frequencies, designated as observed, in Table I are the hypothetical centers of the unperturbed lines and are the frequencies which enter the fit for the other spectroscopic constants. The ground state rotational constants were fixed to the values reported earlier (1). The observed frequencies were assigned a weight inversely proportional to the square of their estimated uncertainties: 0.003 cm-r for unblended lines, 0.006 for portly blended lines. Badly overlapped lines were left out from the fit. In the first fit, only y0 and a’ were allowed to float, all other rotational constants being constrained either to their values as calculated from the (Y’Sobtained from the analysis of the 2~1 band (I), or to their values in the ground vibrational state. Other upper state constants were progressively allowed to float in successive fits which included the frequencies of an increasingly larger number of assigned transitions. Because no lines belonging to series with values of K, < 4 (where the effect of the molecular asymmetry is largest) could be used in the fit, constants largely dependent upon the molecular asymmetry could not be determined. The distortion constants 8x and 8~ were therefore fixed to their ground state values. Moreover, although @ + C?is well
THE
YXBAND TABLE
Spin Rotation
Easa-
Coupling
Constants
('bb + 'CC)
in cm+
III Determined
for the v1 Band
of NO2
0.18643 (83)'
0.181b44a
'bb + 'CC
433
OF “N”Oz
-0.0014b08a
-0.001630 (29)
b -1.68 (9) x 10-4
-1.704 (33) x 1oc4
2
" aaaa
determined by the data, the difference is not; therefore either B or C? had to be constrained to the value calculated using the Q’S from 2~ I. The two different sets of constants thus calculated were identical to within a small fraction of a standard deviation. TABLE Upper
State Rotational
Constants
IV
(in cm-l)
of the v1 Band
A
8.09136 (391C
8.09134 (39)'
6
0.4313834 (33)
0.4313482 (80)
C
0.4078214 (74)
0.4078587 (31)
B+c
0.8392048 (81)
0.8392069 (86)
n
2.8132 (76) x 10-3
c 6 N 6 K 6 N
“K %N
-5 -1.799 (13) x 10
2.8126 (76) x 1O-3 -1.795 (14) x 10-5
3.0169 (81) x lO-7
-7 3.0123 (68) x 10
4.13 (57) x 10-6d
-gd 4.13 (57) x 10
-sd 3.103 (32) x 10
-ad 3.103 (32) x 10
-6 2.896 (46) x 10 -8 -3.54 (13) x 10
2.891 (46) x lO+ -8 -3.51 (14) x 10
34
5.4 (20) x lo-13d
-13d 5.4 (20) x 10
"0
1319.7973 (64)
1319.7975 (64)
of 14N1602
434
LAURIN
AND CABANA
The Hamiltonian used has been described previously (I, 3, 12). The spectroscopic constants obtained from such fits are reproduced in Table IV. It is realized that neither CBnor e are thus determined but only their sum. New attempts will be made to measure series involving levels with values of K, < 4, but there is little hope that such experiments will be entirely successful. It is not impossible that hot bands in the electronic spectrum would provide the desired additional information. ACKNOWLEDGMENTS We would like to thank Dr. A. G. Maki for supplying us with a copy of the asymmetric rotor program used. We are indebted to Dr. W. J. Lafferty for several instructive conversations. Continued financial assistance from the “Minis&e de 1’Education de la Province de Quebec” and from the National Research Council of Canada is gratefully acknowledged.
RECEIVED: September
15, 1977 REFERENCES
1. A. CABANA,M. LAURIN,W. J. LAFFERTY,ANDR. L. SAYS, Cased. J. Phys. 53,1902 (1975). 2. S. C. HURMCK, K. NARAEARIRAO, L. A. WELLER, ANDP. K. L. YIN, J. Mol. Speclrosc. 48, 372 (1973). 3. A. CABANA,M. LAURIN, C. PEPIN, ANBW. J. LAFPERTY,J. Mol. Speclrosc. 59, 13 (1976). 4. S. C. HURIX)CK,W. J. LAFFERTY,ANDK. NA~A~IARIRAO, J. Mol. Spectrosc. 50,246 (1974). 5. E. T. ABAKAWAANDA. H. NIELSEN, J, Mol. Sfiectrosc. 2,413 (1958). 6. J. GXGUERE,M. Sci. Dissertation, Universite de Sherbrooke, 1969. 7. G. GUZZACHVILI,Private communication. 8. J. W. C. JOHNSANDW. B. OLSON,J. Mol. Spectrosc. 39, 479 (1971). 9. G. E. MCGRAW,D. L. BERNIT, ANDI. C. HISATSUNE,J. Chem. Phys. 42,237 (1965). 10. A. GOLDMAN,T. G. KYLE, ANDF. S. BONOMO,A#. Opt. lo,65 (1971). il. R. G. SNY~~ER AM) I. C. HISATSUNE,J. Mol. Spedrosc. I, 139 (1957). 12. W. J. LAFFERTYANDR. L. Sms, Mol. Phys. 28,861 (1974).
High Resolution Infrared MICHEL
(1978)
Spectrum of the
LAURIN
AND ALDEE
v1
Band of 14N160,
CABANA
Department de Chimie, Univers& de Skerbrooke, Sherbrooke, Quebec, Canada JlK
ZRl
The infrared spectrum of the ~1 band of i4Ni60z has been recorded with a resolution about 0.025 cm-i in the region extending from 1480 to 1270 cm-‘. From about 1350 cm-i, absorption became progressively weaker and no absorption at all could be detected below band origin located at 1319.797 cm-i. Because series with low values of K. could not measured, constants which depend strongly upon the molecular asymmetry could not determined.
of the the be be
INTRODUCTION The absorption spectra of two fundamental bands, YZ(I, 2) and ~3 (3, 4), as well as those of several overtone and combination bands (see ref. (I)) have already been obtained under high resolution. However, no high resolution data have yet been reported for the weak ~1 fundamental. In their classic study of the infrared spectrum of several bands of nitrogen dioxide, Arakawa and Nielsen (5) have pointed out that the symmetric stretching vibration VI presented the most serious difficulty with regard to experiment and analysis. Although the spectrometer available to these authors did not allow the resolution of the individual vibration-rotation lines, Arakawa and Nielsen have recognized that internal intensity anomalies were such that the band origin is located completely outside the region of absorption. This paper presents the high resolution infrared absorption spectrum of the ~1 band of NO2 and its analysis.
EXPERIMENTAL
DETAILS
The spectra were obtained with the 2.5-m vacuum spectrometer at the Universite de Sherbrooke (6), in the eighth and ninth order of the grating and calibrated with the 1 c 0 absorption frequencies of carbon monoxide as measured by Guelachvili (7). The region extending from 1480 to 1270 cm-’ has been scanned but no absorption has been found below 1320 cm-i. The scan to the high frequency side is not limited by the usual intensity falloff but rather by the fact that the y1 band runs into absorption by the P side of the much stronger v3 band. Absorption lines below 1335 cm-’ were very weak and their assignment remained uncertain. Therefore none of these could be included in the fit. The working resolution was about 0.025 to 0.030 cm-‘. Strong lines could be measured, in this region, with a precision of about 0.003 cm-’ or slightly better as indicated by the standard deviation of the fit (8) which was 0.83. 421 0022-2852/78/0693-0421$02.00/0 Copyright Q 1978 by Academic Prew. Inc. AU rights of reproduction in any form reserved.
422
LAURIN
*d.s
AND CABANA
d
0
l&o
FIG. 1. The ZQvibration-rotation band of 14N1BO* recorded at about 90°C with a spectral slit width of 0.025 to 0.030 cm-l and an absorption path of 16 m. The sample pressure was about 10 Torr from 1480 to 1376 cm-’ and about 35 Torr to the lower wavenumbers. The strong lines observed below 1350 cm-l do not belong to nitrogen dioxide.
The sample of NOz, obtained from Matheson of Canada Ltd., was found to contain appreciable quantities of CO2 and NO. These impurities were removed by condensing the gas at -79°C in a trap and pumping over the solid until it became white (I). A multiple path absorption cell was used and, since y1 is extremely weak, it was necessary to use long paths and relatively high sample pressures. Absorption by nitric acid and dinitrogen tetroxide, the former present as an impurity and the latter in equilibrium with NOz, has hampered us from using either very long path lengths or higher sample pressures which would have provided us with the desirable absorption at the lower frequencies. It is known (9,lO) that the v3 and vI bands of nitric
THE VI BAND OF “N’602
14oi.5
14oA.5
15d.O
1596.5
03:.5
1581.0
1401.0
,554.O "O,,; PO,i K.*4
14oLA.o
WA5
423
,,s:
5
l5d.5
Ins:*
IS7A.S
FIGURE1-Continued
acid absorb strongly in the region extending from 1370 to 1270 cm-‘. A simple calculation, using the data reported (IO), shows that, with an absorption path of 16 m, 0.03 to 0.04 Torr, HN03 would lead to complete absorption over the entire region specified above. A freshly purified sample of NO2 showed only weak absorption by nitric acid but in a matter of no more than a few hours absorption by HNOl became so intense that the sample had to be replaced. One of the strongest bands of dinitrogen tetroxide, VII, is centered around 1261 cm-l and from the data previously reported (II) it is estimated that with a path length of 16 m, 05Torr Nz04 would lead to complete absorption between 1320 and 1220 cm-‘. This has limited the sample pressure to 35 Torr since higher pressures would require higher temperatures which favor rapid formation of HNOa. We have used sample pressures in the range of 10 to 3.5 Torr, a path length of 16 m, and a temperature of 90°C. A compressed scan of the band is reproduced in Fig. 1.
424
LAURIN
AND CABANA
I
l36l.O
1364.0
13d.o
,33&o FIGURE
LINE ASSIGNMENT
l-Continued
AND INTENSITY
ANOMALIES
Line assignment in this band, like in any other B-type band of NOz, was complicated by the spin splitting, but the most serious complications arose from intensity anomalies which are greater in this band than in any other band of nitrogen dioxide. These anomalies may be briefly described as follows: on the low frequency side of the band origin no absorption line was intense enough to be measured, and on the high frequency side, absorption was very weak for the lowest values of K, but it increased progressively with increasing values of K until it blended with the much stronger absorption from v3. Furthermore lines which are expected strongest are weakest and vice versa. More explicitly, no PQK-, pPK-,and PR&ype transitions were found but only, transitions were in order of decreasing relative intensities, RP~-,RQK-, and a&-type observed. These unusual intensity perturbations are thus more severe in VI than in 2~1 (I) where, in turn, they are more severe than in 213 (II), but in no case does there appear
THE
~1 BAND
425
OF “N”Oz
134.0
131;.5 FIGURE I-Continued
to be any frequency perturbation. Figure 2 shows a selected portion of the spectrum which illustrates these anomalies. After several false starts a series of lines was assigned to transitions of the RP4 branch. This assignment was verified since line frequencies of the RQP series could be precisely predicted from these RP4 transitions and the accurately known ground state energies. After a certain number of lines had been assigned, these were used to obtain the frequency of the band origin, ~0, and the upper state rotational constant a’. These newly determined constants were used to extrapolate the line assignment further. All line
V
I
24 I
23 v 38
V
39
I
1406.5
V
25
v 40
V
26
27
V
41
v 42
2s P 43
I
1403.5
FIG. 2. Selected portion of the ~1 band illustrating the intensity anomalies and the spin splitting.
W
7
0 0 l 0 0 5 0 5 0 5 5
c
.”
W .Z
oc
*I’
.
. . . . . . . . . . . .
.
91
oc sz
zc
.
. .
.
oa
ZL
.a
ez
El .I b 9 . 0 9. . . t. 0. OF PC .I .I .I a!* .I . 5. I. 4s LC OS
. . . . . . . . * .
cc
.
.
.
.
B.? 92 :; 01 0, 9, .I II 0,
.PY
.
01 I, 61 Cl II
9
s
.z
6
PY
11
5 5 0 0 0 6 5 5 5 5 5 6 5 5 0 6 5
PO .I II 01 01 .I 10
a.?
5
6.
. .
. . . . . . . .
ci ,a
0, 91 .I 11 01 0 0 .
.
z .. . .
1
.
. . l . PC
.
1. 0.
.P
. .
oc
oc
.c
0. *. .P 91 SC 01
or
ON
EC
. .
La! SL
w
1s
5 . . . . . . . t . . . . . . . . . . .
I 318V.L
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
1
l
.
.
.
.
.
.
.
4
. . . .
OISLRVLD
-e..** -0.b.b. ..o.J7 0.00.. -0.00.. . . . . . 0....7 . ..O.. -....J. -.* 0.03 0...2* -0.0011 -0.0.5. -...,I, -0. ..s7 0.0.03
..a
-0.001. -0. ..a. . . ..I* -....JJ -....1. 0.003. . ...11 -0.003. -0.0077 . . ..U 0.003. 0.0.2, . . . -0.002. 4.002,
. ..a. -.....* ..-
..oon -....a. -...... . . ..I.
0.n.I -....,. . ..07. ~..01. -0.0011 -0.o.w -.....* -0.0U. -0.000. . . . .
-.....I
o-c . ...7.
TABLE I-Continwd
-
-
3. . .
.a
6
0
0
0
0
0
e
0
-
-
a. aa .7.
0 0 1. IP 1. I. ,.
.-
6 0
0
6 * -
-
s.
0
.
-
1. 3. 3P 3.
l . 0 0
.o.u ..nu
.
a*
73 I7
a
91
a.
0 (1 13 IS I7
..
.7 4.n.a 4.oa7 -...... 4.n.. -..m 4.n.7 -.a... 4rY.b 4.m -..-a 4.“PI 4d.m 4....b 4...m 4...4. 4d.b. . ..“7 . ..I.. -.a.., -...... 4.n.. -.....I -....J. 4.n.. -*...sa 4.m.. 4...s7 4d.n -...W. 4o.n. -0.o.n 4d.a. ..OII3 4.W. -.....J 4.nrs 4.a.. 4.o.m . . ..I. -...a. . . .
..owo
..a..
l .aaJ l .n.0
.3
.s
l
.a
3. 37 s7
O-C 04.7. ..Y
0
01
PI .I Ll
I.
.*
P
0. OP PC
K;
K;
TABLE I-Continued
I
-..oom
-0.00.3
0.0053 0.003s
O.OOL.
0.0003
-0.00,
L
O.COOS
-0.004,
‘0.0085
-0.00~0 -0.0*35 0.0005 -0 .oo.
-0.0120
0.0005 -0.0005 O.OO.?B 0.0005 -0.0026 -0.0091
-o.ooo*
0.0014
0.0022
0.0931
-0.0013
-0.0012 -0.OoOT
0.0221 0.0070
0.0092 O.OL61
o-c
TABLE I-Continued
THE ~1 BAND TABLE
OF 14N’60z II
Observed and Calculated Spin Splittings (cm-‘)
Transition
Ilvoba AYobs-Avc.lc
%,3 - 94,6 to.220 lO5.5 - 114.8
to.164
431
in the Ye Band of L4N1(02
Transition
Avobs Auob,-Avc,lt
-0.015
166,10 - 175,13 to.126
to.002
-0.001'
167.9 - 176,12 to.158
-0.008
125,7 - 134*10 to.141
-0.011
177,11 - 1B6*12 to.152
-0.003
145.9 - 154,12 to.123
-0.006
207,13 - 216,16 to.123
-0.007
165,11 - 174.14 to.108
-0.003
257,19 - 266,20 to.097
-0.003'
175,13 - 184,14 to.114
to.009
267,19- 276,22 +0.088
+0.008a
18 - 194,16 to.091 5.13
-0.006'
297,23 - 306,24 to.082
-0.002
195,15 - 204,16 to.090
-0.002
307,23- 316,26 to.069
-0.006
205,15 - 214*_
-0.006
130.6 - 147.7
to.230
t0.005.
215,17 - 224,18 to.066
-0.009'
158,8 - 167,9
to.198
-0.010
2$19
-0.007'
198.12 - 207,13 to.149
-0.010
265.21 - 274,24 to.062
-0.003
2211.14 - 23,,17 to.123
-0.012
275,23 - 204s24 to.059
-O.OOla
236,16- 247,17 to.113
+o.olsa
"5.23 - 294,26 to.048
-0.003
278,20 - 2137,21to.097
-0.010
295.25 - 304,26 +0.043
-0.010
268,20 - 297,23 to.092
-0.012.
-0.009
298.22 - 307,23 +o.ow
-O.O1oa
-0.002
30*,22 - 317,25 to.085
-0.011
+o.oOOa
318,24 - 327,25 to.083
-0.008
+o.on1
- 254,22 to.064
96.4 - lO5.5
to.249
136.8 - 145.9
to.153
156,10 - 165,11 to.132
assignments were verified by calculating the appropriate ground state combination differences. The frequencies of the observed lines used in the final fit together with those calculated using the final set of constants are reported in Table I. DATA
TREATMENT
The splitting produced by spin-rotation interaction is quite large in this B-type band. The measured splittings, given in Table II, were fit in the manner described previously using expressions which are good through the second order (I). The third term of those expressions, which is the only one determining (w, - e,,), arises because of the asymmetry of the molecule. It is usually invoked only for the K, = 1 levels. It had to be left out from the fit since no transitions involving such levels could be measured and therefore the value of (t W,- eec) could not be calculated for VI. The constants obtained from a least-squares fit, with the ground state E’Sand qaoaa fixed to the values reported (I), are given in Table III. These spin-rotation constants were then used to correct the average frequency obtained for a spin split line for the shift resulting from the asymmetry in the spin
432
LAURIN TABLE
Transition
CABANA
II-Cmtinued
TransitIon
AVobe
Avobs-Ay CdC
to.192
-0.014
356.30 - 365,31 to.053
-0.003
209,11- 21g,14 to.159
+o.o05a
366,30 - 375,33 to.048
-0.006.
Q3
-0.005
ll9.9
a
AND
- 18g,lo
"ohs
Avc,bs-Av ClllC
to.001
376,32 - 385,"
239.15 - 2'8,16 to.128
-o.oo3a
"6.34 - 405,35 to.039
-0.010
219,19 - 2a*,20 to.114
-0.008
ll7.5 - 126.6
to.242
-0.009
269.19 - 29*,22 to.104
-0.014
127.5 - 136.8
to.207
-0.021
- 226,14 to.146
to.046
2g9.21- 3og,22 to.102
-o.oloa
l'7*7 - 146.8
to.187
-0.020
"6.14 - 205,15
-0.009*
l57.9 - 166,10 to.161
-0.016
206,14 - 215,17 to.095
-0.012
'09,21 - 31g,24 to.093
-0.015
to.103
216,16 - 225,17 to.092
-0.009a
'19.23 - 328,24 to.089
-0.005
226.16 - 235,19 to.089
-0.006a
359,27 - 368,28 tO.060
-0.002
236,18 - 245,19 to.062
-O.OOla
389.29 - 398,32 to.079
-0.003'
'256,20- 265,21 to.079
to.006
l310.4 - 149,9
to.317
to.002
266 2. - 215 23 to.076 # 276,22 - 285;23 to.064
-0.003
1510.6 - 169,7
to.256
-0.007
2510,16-26g,17 to.143
-0.006'
-0.011
206,22- 295,25 to.073
to.001
3010 20- 319 23 to.116
-0.004
2g6,24 - 305,25 to.067
-0.003*
'%0:26- 379.29 to.089
-0.008
306,24 - 315,27 to.066
to.001
l
THESELINES WERE GIVEN A WEIGHT OF UNITY; ALL OTHERS WERE GIVEN A HEIGHT OF ONE QUARTER
splitting. The line frequencies, designated as observed, in Table I are the hypothetical centers of the unperturbed lines and are the frequencies which enter the fit for the other spectroscopic constants. The ground state rotational constants were fixed to the values reported earlier (1). The observed frequencies were assigned a weight inversely proportional to the square of their estimated uncertainties: 0.003 cm-r for unblended lines, 0.006 for portly blended lines. Badly overlapped lines were left out from the fit. In the first fit, only y0 and a’ were allowed to float, all other rotational constants being constrained either to their values as calculated from the (Y’Sobtained from the analysis of the 2~1 band (I), or to their values in the ground vibrational state. Other upper state constants were progressively allowed to float in successive fits which included the frequencies of an increasingly larger number of assigned transitions. Because no lines belonging to series with values of K, < 4 (where the effect of the molecular asymmetry is largest) could be used in the fit, constants largely dependent upon the molecular asymmetry could not be determined. The distortion constants 8x and 8~ were therefore fixed to their ground state values. Moreover, although @ + C?is well
THE
YXBAND TABLE
Spin Rotation
Easa-
Coupling
Constants
('bb + 'CC)
in cm+
III Determined
for the v1 Band
of NO2
0.18643 (83)'
0.181b44a
'bb + 'CC
433
OF “N”Oz
-0.0014b08a
-0.001630 (29)
b -1.68 (9) x 10-4
-1.704 (33) x 1oc4
2
" aaaa
determined by the data, the difference is not; therefore either B or C? had to be constrained to the value calculated using the Q’S from 2~ I. The two different sets of constants thus calculated were identical to within a small fraction of a standard deviation. TABLE Upper
State Rotational
Constants
IV
(in cm-l)
of the v1 Band
A
8.09136 (391C
8.09134 (39)'
6
0.4313834 (33)
0.4313482 (80)
C
0.4078214 (74)
0.4078587 (31)
B+c
0.8392048 (81)
0.8392069 (86)
n
2.8132 (76) x 10-3
c 6 N 6 K 6 N
“K %N
-5 -1.799 (13) x 10
2.8126 (76) x 1O-3 -1.795 (14) x 10-5
3.0169 (81) x lO-7
-7 3.0123 (68) x 10
4.13 (57) x 10-6d
-gd 4.13 (57) x 10
-sd 3.103 (32) x 10
-ad 3.103 (32) x 10
-6 2.896 (46) x 10 -8 -3.54 (13) x 10
2.891 (46) x lO+ -8 -3.51 (14) x 10
34
5.4 (20) x lo-13d
-13d 5.4 (20) x 10
"0
1319.7973 (64)
1319.7975 (64)
of 14N1602
434
LAURIN
AND CABANA
The Hamiltonian used has been described previously (I, 3, 12). The spectroscopic constants obtained from such fits are reproduced in Table IV. It is realized that neither CBnor e are thus determined but only their sum. New attempts will be made to measure series involving levels with values of K, < 4, but there is little hope that such experiments will be entirely successful. It is not impossible that hot bands in the electronic spectrum would provide the desired additional information. ACKNOWLEDGMENTS We would like to thank Dr. A. G. Maki for supplying us with a copy of the asymmetric rotor program used. We are indebted to Dr. W. J. Lafferty for several instructive conversations. Continued financial assistance from the “Minis&e de 1’Education de la Province de Quebec” and from the National Research Council of Canada is gratefully acknowledged.
RECEIVED: September
15, 1977 REFERENCES
1. A. CABANA,M. LAURIN,W. J. LAFFERTY,ANDR. L. SAYS, Cased. J. Phys. 53,1902 (1975). 2. S. C. HURMCK, K. NARAEARIRAO, L. A. WELLER, ANDP. K. L. YIN, J. Mol. Speclrosc. 48, 372 (1973). 3. A. CABANA,M. LAURIN, C. PEPIN, ANBW. J. LAFPERTY,J. Mol. Speclrosc. 59, 13 (1976). 4. S. C. HURIX)CK,W. J. LAFFERTY,ANDK. NA~A~IARIRAO, J. Mol. Spectrosc. 50,246 (1974). 5. E. T. ABAKAWAANDA. H. NIELSEN, J, Mol. Sfiectrosc. 2,413 (1958). 6. J. GXGUERE,M. Sci. Dissertation, Universite de Sherbrooke, 1969. 7. G. GUZZACHVILI,Private communication. 8. J. W. C. JOHNSANDW. B. OLSON,J. Mol. Spectrosc. 39, 479 (1971). 9. G. E. MCGRAW,D. L. BERNIT, ANDI. C. HISATSUNE,J. Chem. Phys. 42,237 (1965). 10. A. GOLDMAN,T. G. KYLE, ANDF. S. BONOMO,A#. Opt. lo,65 (1971). il. R. G. SNY~~ER AM) I. C. HISATSUNE,J. Mol. Spedrosc. I, 139 (1957). 12. W. J. LAFFERTYANDR. L. Sms, Mol. Phys. 28,861 (1974).