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New measurements in the millimeter-wave spectrum of 14N16O2
JOURNAL
OF MOLECULAR
SPECTROSCOPY
134, 176-182 (1989)
New Measurements in the Millimeter-Wave Spectrum of 14N1602 N. SEMMOUD-MONNANTEUIL AND J.-M. COLMONT Laboratoire de Spectroscopic Hertzienne, UA 249, CNRS, UniversitC de Lille I, 59655 Villeneuve d’Ascq Cedex, France
AND
A. PERRIN, J.-M. FLAUD,
AND
C. CAMY-PEYRET
Laboratoire de Physique Moltkdaire et Atmosphtfrique, Universitk Pierre et Marie Curie et CNRS, Tour 13. 4 Place Jussieu, 75252 Paris Cedex 05. France
One hundredeleven new microwavetransitionsbelonging to the ground state of 14N“‘02 have been observed in the spectral region 180-300 GHz. A discussion of the impact of the earth’s magnetic field leading to an observed Zeeman effect is presented. o 1989 Academic press, h.
I. INTRODUCTION Nitrogen dioxide is a very interesting species to study spectroscopically since it is a chemically stable nonlinear triatomic radical which has an unpaired electron leading to a strong spin-rotation interaction and which exhibits a hyperfme structure. NO2 has been the subject of numerous studies in the microwave, the infrared, and the visible spectral regions, leading to the determination of accurate spin-rotation ground state levels up to high values of J and K, quantum numbers (J G 54, K, G 14). Whereas the spin-rotation splittings are easily resolved, the hyperhne structure is only exceptionally observable. In fact, experimental techniques which allow one to observe easily the hypefine structure include microwave optical double resonance (MODR) (I, 2)) infrared radiofrequency double resonance (IRDR) (3), laser magnetic resonance (4)) and electron paramagnetic resonance studies (5-7) as well as microwave spectroscopy measurements (8-12). Unfortunately, only low K, rotational levels (K, < 4) are available from these studies and, in order to obtain information both on the hyperfme structure of nitrogen dioxide and on high K, rotational levels, it is necessary to combine these results with high-resolution infrared studies. This has been done in Ref. (13) where the microwave, MODR, and IRDR experimental data (l-3, 8-12) were combined together with new infrared results in order to derive the best possible set of rotational, spin-rotation, and hyperfme constants. These parameters were then used to compute a synthetic spectrum of the (000) + (000) band of NO* covering the spectral region O-230 cm-’ allowing one to assign easily the new microwave NOz transitions presented in this paper. 0022-2852189 Copyright 0
$3.00
1989 by Academic Press Inc.
All rights of reproduction in any form reserved.
176
MILLIMETER
177
SPECTRUM OF “N’602
v- v,
,-
b
-2
-1
1
0
2
MHz
FOG.1. Zeeman effect due to the earth’s magnetic field on the [J’ = 6.5, F’ = 6.51~ [J” = 5.5, F” = 6.51 component of the [ 6 15 ] + [ 606 ] rotational transition of NO*. Upper trace: the Zeeman “doublets”. Lower trace: the same spectral region recorded when compensating for the earth’s magnetic field. The line center frequency is v, = 234 766.13 MHz.
II. EXPERIMENTAL
DETAILS
The sample of NO2 was purchased from 1’Air Liquide and used without further purification. TABLE I Calculated and Observed Positions of the (J’ - N’ # J” - N”) and (F’ = F”) Components of the
[ 6 151 + [ 6061 Rotational Transitions of 14N1602; Due to the Earth’s Magnetic Field the Lines Are Split into Doublets by the Zeeman Effect N' K; Kc
6
6
6
6
1
1
1
1
5
5
5
5
J'
5.5
5.5
6.5
6.5
F'
5.5
5.5
5.5
6.5
N" K"a K"c
6
6
6
6
0
0
0
0
6
6
6
6
J"
6.5
6.5
5.5
5.5
F"
5.5
5.5
5.5
6.5
Obs
Calc
234350.70
234350.65
i 234352.27
234352.54
234500.27
234500.08
234502.48
234502.17
234618.49
234618.39
234620.20
234620.56
234765.32
234765.35
234767.03
234767.32
i
1
i
Note. N’ KL Kc J’ F’, N” K”, K: J” F”: upper and lower rotational quantum numbers. Ok observed frequencies (in MHz). Calc: calculated frequencies (in MHz) of the (ML = A45 = -tF’ = ?F”) Zeeman components.
MILLIMETER
179
SPECTRUM OF “N’602
TABLE II-Continued N KA KC
J
FNKAKC
J
F
0
LOWER
UPPER
21 1 21 23 2s 2:
-"L -l/Z
y
i '2! * -l/2 1 2: -112 1 2: 112
0 1 0
*
25 1 25 li2 -i $2 d 1 ! 25 -l/2 -1,'2 -1 2'; 1 2'; 1;;; 7 ;:
i 2E 1 25
'i2 -1 l/2 3
2i
1 25
1'2
% 32 32 35 34 3;
21 2 2 2 2 ;
57 4F 45 45
.i 2 3s % 4s ;' 4' 5 4;
$ 45 52
'; 4: 3 SC 1:2 -1 '12 0 4'; 112 1 ? 40 -112 -1 ;
2: 3" -l/2 lj2 A 0 30 l/2 0 35 l/2 -1 32 -l/2 1 32 l/2 0 g -'/2 -1 -1!2 -1,'2 51 -112 1 -1:2 0 -l/2 -1
OBS
O-C
MHZ
MHZ
242820.46 242942.82 2'34'!.83 213697.30 216697.66 215164.25 107277.3' 137400.55 167432.32 '87C76.45 '8aa76.76 '88923.92 '66985.16 '69377.87 274872.28 275278.87 275575.55 212699.54 213500.03 239317.67 239334.92 239549.66 196088.28 196092.96 196095.46 196338.65 19&343 16 196351:68 213616.94 213623.60 213528.72 2'3626.70 2'3833.66 213833.68
-c.os -;:;z 8:8'5 2.05 g:;: 3.37 C.lC Oc::: c.10 ;:;: -5.16 -0.17 C1.07 -0.12 -5.13 -3.1: -0.04 G.14; -'J.lO -9.07 -2.32 %:; +:;8 -(;.07 -0.09 -,s.ic! -c;.21
The absorption cell is a 3 m-long, K-band waveguide. The measurements were carried out at pressures of 0.01-0.02 Torr and at a temperature of 260 K. The millimeter-wave power was generated by a frequency multiplier equipped with a Schottky barrier diode, the fundamental frequency being provided by phase-locked Varian klystrons operating from 6 1 to 82 GHz. The absorption spectrum was detected with a Schottky barrier detector. For signal recovery, a frequency modulation at 25 kHz was applied to the klystron. The second-derivative lineshapes resulting from lockin detection at 50 kHz were finally processed in a 256channel digital averager. The uncertainty in the measurements of the line positions is about 0.05 MHz, and it can reach 0.15 to 0.20 MHz for the weakest lines. III. DI!XXJSSION
In a first step, the measurements were performed without compensating for the earth’s magnetic field: the cell orientation was east-west and the polarization of the microwave source was roughly parallel to the earth magnetic field. Consequently, the most visible Zeeman effect was observed for lines with J’ - N’ # J” - N”
(1)
F’ = F”.
(2)
Indeed, because of the condition given in Eq. (1)) the Zeeman effects in the upper and lower state of the transitions do not compensate each other. Consequently, as
TABLE III Molecular Constants for the (000) State of 14N1602 Constant (Cm- )
u
ConStant IUEIZ)
8.00235469
+ 0.00000035
0.422074669
+ 0.000000024
(0.58160646,
239904.5582
f 0.00000038) x 10-x
0.433706798
13002.20271
0.410442540 (0.2687875,
12304.75778 80.580486
+ 0.0000041) x 10-a
C-O.1968220
f 0.000012)
x 10“
(0.299244,
f 0.000034~
x 10-e
(0.40547
f 0.00042) x lo-"
0.121557
CO.3192707 . (0.30315
+ 0.000034) x lo-'
0.9571697 x lo-'
+ 0.00015) x lo-'
0.908841 x lo-'
f 0.00027) x lo-'
-0.810755 x 10-a
t-0.27043:
-0.5900575 0.8971131 x 10-a
(0.299
+ 0.020) x 10-10
0.8980 x 10-s
(0.286:
+ 0.01) x lo-"
0.8592 x 10-e
(0.2929
+ 0.0086) x lo-'
0.87829 x 10-5
f-0.363,'
f 0.028) x lo-'*
-0.109023 x 10“
10.1057
f 0.0017) x lo-'*
(-0.5110:
0.31688 x lo-'
f 0.0022) x 10“
-0.153206 x 10-l
lO.3511,
?r0.0013) x 10-10
0.105277 x lo-'
(0.1215,
f 0.097) x lo-'2
0.36450 x lo-'
(0.867
+ 0.0131 x lo-"
(-0.843: -0.1024408,, 0.148449810 1+0.171797 0.180353;;6
+ 0.030) x lo-'*
0.25993 x 10-s -0.2530 x lo-'
f 0.0000014 f 0.0000019 f 0.0000123 x 10-z 5406.84710
0.257833 x 10-l
7.72963
-0.3178107 x 10-a
-95.277263
l-O.176060 CO.600
f 0.025) x lo-'
0.18003 x 10-1
(0.167:
* 0.011) x lo-'
0.5029 x lo-'
10.632
+ 0.066) x lo-'
0.18953 x lo-'
10.376:
+ 0.056) x lo-‘
0.11300 x 10-1
IO.244
t 0.0401 x 10“
0.7314 x lo-'
10.296;
f 0.0060) x lo-‘
0.88958 x 10-z
f 0.00036l x 1O-a
(-0.356,'
f 0.025) x lo-*
(0.491294I, (-0.36817I‘
?.0.000044) x lo-'
(0.39256,,
f 0.00068) x 10“
-22.075016
0.1329764 x 1O-2 ,-0.191;:, TIb IW)
-0.10697 x lo-' 147.286334
c 0.00039) x 10-a
-0.7363433 x lo-> (0.752
-5.27814
39.865321 k 0.040) x 10-1 t 0.0024, x lo-'
0.15054 x 10-a
0.45131
-0.544976 x lo-'
-1.633798
Note. The quoted errors are one estimated standard deviation. For the spin-rotation constants the convention for the rt( 6) is given in Table I of Ref. (14), and for the hyperfine constants (magnetic and electric quadrupole) we have
mm =; x,,,
%(X) = &(2X& +&A. 180
MILLIMETER
SPECTRUM OF “N’602
181
shown in Fig. 1, each line splits into two groups of MF components, the intensities of which are roughly proportional to ( MF)’ as these lines obey the selection rule given by I+. (2). Consequently the strongest components correspond to M> = M> = + F, for which the Zeeman splitting is the most important. As an example, we give in Table I the Zeeman “doublets” observed for the [J = N’ + 1, F’ = j”‘] c [J” = N” 7 f, F”] components ofthe [N’ = 6, Kh = 1, Kk = 5]* [N” = 6,K: = 0,K’f = 61 rotational transition (the other hyperhne components of this same rotational transition are not significantly affected by the Zeeman effect). We have also evaluated the position of the MF = + F doublets. For this purpose, we used an estimated earth magnetic field of 0.46 G and the Zeeman parameters of Ref. ( 7) as well as the molecular parameters of Ref. (13) and the phase convention and definition of spectroscopic constants of Refs. ( 7, 14, 15). As can be seen in Table I, the observed “doublets” are accurately reproduced by the calculation, showing clearly that the shifts can be accounted for by the Zeeman effect. We have checked that it is also the case for all the AJ = + 1, AF = 0 hyperfme components of the [N, 1, N - l] + [N, 0, N] rotational series observed in the present work. Then using coils in order to compensate for the earth magnetic field, we have observed that the shifts disappeared and the final results given in Table II were obtained under this condition. Most of these newly observed transitions correspond to weak (A J # AF) components which have been assigned using the computed spectrum generated in Ref. ( 13). The agreement between observed and calculated values is excellent and the molecular parameters obtained including this new set of experimental data are given in Table III. They differ only slightly from those of Ref. (13). CONCLUSION
Using a synthetic spectrum of the (000) + (000) band of “N’602 it has been possible to assign easily 111 new weak transitions of this molecule observed by means of microwave spectrometry. ACKNOWLEDGMENTS The authors are indebted to Dr. J. M. Brown for the communication of his least-squares fitting program written for nonsinglet asymmetric rotors with one-nucleus hyperfme interactions. RECEIVED:
October 14, 1988 REFERENCES
D. 0. HARRIS, J. Chem. Phys. 59, 5217-5218 (1973). 2. J. M. BROWN, T. C. STEIMLE, M. E. COLES, AND R. F. CURL, JR., J. Chem. Phys. 74, 3668-3672 (1981). 3. M. ALLEGRINI, A. R. W. MC KELLAR, P. PINSON, AND J. M. BROWN, J. Chem. Phys. 73,6086-6089 (1980). 4. R. F. CURL, JR., K. M. EVENSON, AND J. S. WELLS, J. Chem. Phys. 56,5143-5 151 (1972). 1.
T.
TANAKA, A. D. ENGLISH, R. W. FIELD, D. A. JENNINGS, AND
182
SEMMOUD-MONNANTEUIL
5. T. J. SCHAAFSMA, Chem.
ET AL.
Phys. Lett. 1, 16-18 (1967).
6. D. S. BURCH, W. H. TANTILLA, AND M. MIZUSHIMA, J. Chem. Phys. 61, 1607-1612 (1974). 7. J. M. BROWN AND T. J. SEARS, Mol. Phys. 34, 1595-1610 (1977). 8. G. R. BIRD, J. C. BAIRD, A. W. JACHE, J. A. HODGENSON, R. F. CURL, JR., A. C. KUNKLE, J. W. BRANSFORD, J. RASTRUP-ANDERSEN,AND J. ROSENTHAL, .I. Chem. Phyx. 40,3378-3390 (1964). 9. R. M. LEES, R. F. CURL, AND J. C. BAKER, J. Chem. Phys. 45,2037-2040 (1966). IO. P. A. BARON, P. D. GODFREY, AND D. 0. HARRIS, J. Chem. Phys. 60.3723-3624 (1974). Il. W. C. BOWMAN AND F. C. DE LUCIA, J. Chem. Phys. 77,92-107 (1982). 12. 0. I. BASKAKOV, M. V. MOSKIENKO, AND S. F. D~UBKO, Opt. Spectrosc. (USSR) 53,270-272 (1982). 13. A. PERRIN, J. M. FLAUD, C. CAMY-PEYRET, B. CARLI, AND M. CARLOTTI, Mol. Phys. 63,791-810
(1988). 14. I. C. BOWATER, J. M. BROWN, AND A. CARRINGTON, Proc. R. Sot. A 333,265-288 (1973). IS. C. E. BARNES, J. M. BROWN, A. CARRINGTON,J. PINKSTONE,T. J. SEARS, AND P. J. THISTLETHWAITE, J.
Mol. Spectrosc. 72, 86-101 (1978).
OF MOLECULAR
SPECTROSCOPY
134, 176-182 (1989)
New Measurements in the Millimeter-Wave Spectrum of 14N1602 N. SEMMOUD-MONNANTEUIL AND J.-M. COLMONT Laboratoire de Spectroscopic Hertzienne, UA 249, CNRS, UniversitC de Lille I, 59655 Villeneuve d’Ascq Cedex, France
AND
A. PERRIN, J.-M. FLAUD,
AND
C. CAMY-PEYRET
Laboratoire de Physique Moltkdaire et Atmosphtfrique, Universitk Pierre et Marie Curie et CNRS, Tour 13. 4 Place Jussieu, 75252 Paris Cedex 05. France
One hundredeleven new microwavetransitionsbelonging to the ground state of 14N“‘02 have been observed in the spectral region 180-300 GHz. A discussion of the impact of the earth’s magnetic field leading to an observed Zeeman effect is presented. o 1989 Academic press, h.
I. INTRODUCTION Nitrogen dioxide is a very interesting species to study spectroscopically since it is a chemically stable nonlinear triatomic radical which has an unpaired electron leading to a strong spin-rotation interaction and which exhibits a hyperfme structure. NO2 has been the subject of numerous studies in the microwave, the infrared, and the visible spectral regions, leading to the determination of accurate spin-rotation ground state levels up to high values of J and K, quantum numbers (J G 54, K, G 14). Whereas the spin-rotation splittings are easily resolved, the hyperhne structure is only exceptionally observable. In fact, experimental techniques which allow one to observe easily the hypefine structure include microwave optical double resonance (MODR) (I, 2)) infrared radiofrequency double resonance (IRDR) (3), laser magnetic resonance (4)) and electron paramagnetic resonance studies (5-7) as well as microwave spectroscopy measurements (8-12). Unfortunately, only low K, rotational levels (K, < 4) are available from these studies and, in order to obtain information both on the hyperfme structure of nitrogen dioxide and on high K, rotational levels, it is necessary to combine these results with high-resolution infrared studies. This has been done in Ref. (13) where the microwave, MODR, and IRDR experimental data (l-3, 8-12) were combined together with new infrared results in order to derive the best possible set of rotational, spin-rotation, and hyperfme constants. These parameters were then used to compute a synthetic spectrum of the (000) + (000) band of NO* covering the spectral region O-230 cm-’ allowing one to assign easily the new microwave NOz transitions presented in this paper. 0022-2852189 Copyright 0
$3.00
1989 by Academic Press Inc.
All rights of reproduction in any form reserved.
176
MILLIMETER
177
SPECTRUM OF “N’602
v- v,
,-
b
-2
-1
1
0
2
MHz
FOG.1. Zeeman effect due to the earth’s magnetic field on the [J’ = 6.5, F’ = 6.51~ [J” = 5.5, F” = 6.51 component of the [ 6 15 ] + [ 606 ] rotational transition of NO*. Upper trace: the Zeeman “doublets”. Lower trace: the same spectral region recorded when compensating for the earth’s magnetic field. The line center frequency is v, = 234 766.13 MHz.
II. EXPERIMENTAL
DETAILS
The sample of NO2 was purchased from 1’Air Liquide and used without further purification. TABLE I Calculated and Observed Positions of the (J’ - N’ # J” - N”) and (F’ = F”) Components of the
[ 6 151 + [ 6061 Rotational Transitions of 14N1602; Due to the Earth’s Magnetic Field the Lines Are Split into Doublets by the Zeeman Effect N' K; Kc
6
6
6
6
1
1
1
1
5
5
5
5
J'
5.5
5.5
6.5
6.5
F'
5.5
5.5
5.5
6.5
N" K"a K"c
6
6
6
6
0
0
0
0
6
6
6
6
J"
6.5
6.5
5.5
5.5
F"
5.5
5.5
5.5
6.5
Obs
Calc
234350.70
234350.65
i 234352.27
234352.54
234500.27
234500.08
234502.48
234502.17
234618.49
234618.39
234620.20
234620.56
234765.32
234765.35
234767.03
234767.32
i
1
i
Note. N’ KL Kc J’ F’, N” K”, K: J” F”: upper and lower rotational quantum numbers. Ok observed frequencies (in MHz). Calc: calculated frequencies (in MHz) of the (ML = A45 = -tF’ = ?F”) Zeeman components.
MILLIMETER
179
SPECTRUM OF “N’602
TABLE II-Continued N KA KC
J
FNKAKC
J
F
0
LOWER
UPPER
21 1 21 23 2s 2:
-"L -l/Z
y
i '2! * -l/2 1 2: -112 1 2: 112
0 1 0
*
25 1 25 li2 -i $2 d 1 ! 25 -l/2 -1,'2 -1 2'; 1 2'; 1;;; 7 ;:
i 2E 1 25
'i2 -1 l/2 3
2i
1 25
1'2
% 32 32 35 34 3;
21 2 2 2 2 ;
57 4F 45 45
.i 2 3s % 4s ;' 4' 5 4;
$ 45 52
'; 4: 3 SC 1:2 -1 '12 0 4'; 112 1 ? 40 -112 -1 ;
2: 3" -l/2 lj2 A 0 30 l/2 0 35 l/2 -1 32 -l/2 1 32 l/2 0 g -'/2 -1 -1!2 -1,'2 51 -112 1 -1:2 0 -l/2 -1
OBS
O-C
MHZ
MHZ
242820.46 242942.82 2'34'!.83 213697.30 216697.66 215164.25 107277.3' 137400.55 167432.32 '87C76.45 '8aa76.76 '88923.92 '66985.16 '69377.87 274872.28 275278.87 275575.55 212699.54 213500.03 239317.67 239334.92 239549.66 196088.28 196092.96 196095.46 196338.65 19&343 16 196351:68 213616.94 213623.60 213528.72 2'3626.70 2'3833.66 213833.68
-c.os -;:;z 8:8'5 2.05 g:;: 3.37 C.lC Oc::: c.10 ;:;: -5.16 -0.17 C1.07 -0.12 -5.13 -3.1: -0.04 G.14; -'J.lO -9.07 -2.32 %:; +:;8 -(;.07 -0.09 -,s.ic! -c;.21
The absorption cell is a 3 m-long, K-band waveguide. The measurements were carried out at pressures of 0.01-0.02 Torr and at a temperature of 260 K. The millimeter-wave power was generated by a frequency multiplier equipped with a Schottky barrier diode, the fundamental frequency being provided by phase-locked Varian klystrons operating from 6 1 to 82 GHz. The absorption spectrum was detected with a Schottky barrier detector. For signal recovery, a frequency modulation at 25 kHz was applied to the klystron. The second-derivative lineshapes resulting from lockin detection at 50 kHz were finally processed in a 256channel digital averager. The uncertainty in the measurements of the line positions is about 0.05 MHz, and it can reach 0.15 to 0.20 MHz for the weakest lines. III. DI!XXJSSION
In a first step, the measurements were performed without compensating for the earth’s magnetic field: the cell orientation was east-west and the polarization of the microwave source was roughly parallel to the earth magnetic field. Consequently, the most visible Zeeman effect was observed for lines with J’ - N’ # J” - N”
(1)
F’ = F”.
(2)
Indeed, because of the condition given in Eq. (1)) the Zeeman effects in the upper and lower state of the transitions do not compensate each other. Consequently, as
TABLE III Molecular Constants for the (000) State of 14N1602 Constant (Cm- )
u
ConStant IUEIZ)
8.00235469
+ 0.00000035
0.422074669
+ 0.000000024
(0.58160646,
239904.5582
f 0.00000038) x 10-x
0.433706798
13002.20271
0.410442540 (0.2687875,
12304.75778 80.580486
+ 0.0000041) x 10-a
C-O.1968220
f 0.000012)
x 10“
(0.299244,
f 0.000034~
x 10-e
(0.40547
f 0.00042) x lo-"
0.121557
CO.3192707 . (0.30315
+ 0.000034) x lo-'
0.9571697 x lo-'
+ 0.00015) x lo-'
0.908841 x lo-'
f 0.00027) x lo-'
-0.810755 x 10-a
t-0.27043:
-0.5900575 0.8971131 x 10-a
(0.299
+ 0.020) x 10-10
0.8980 x 10-s
(0.286:
+ 0.01) x lo-"
0.8592 x 10-e
(0.2929
+ 0.0086) x lo-'
0.87829 x 10-5
f-0.363,'
f 0.028) x lo-'*
-0.109023 x 10“
10.1057
f 0.0017) x lo-'*
(-0.5110:
0.31688 x lo-'
f 0.0022) x 10“
-0.153206 x 10-l
lO.3511,
?r0.0013) x 10-10
0.105277 x lo-'
(0.1215,
f 0.097) x lo-'2
0.36450 x lo-'
(0.867
+ 0.0131 x lo-"
(-0.843: -0.1024408,, 0.148449810 1+0.171797 0.180353;;6
+ 0.030) x lo-'*
0.25993 x 10-s -0.2530 x lo-'
f 0.0000014 f 0.0000019 f 0.0000123 x 10-z 5406.84710
0.257833 x 10-l
7.72963
-0.3178107 x 10-a
-95.277263
l-O.176060 CO.600
f 0.025) x lo-'
0.18003 x 10-1
(0.167:
* 0.011) x lo-'
0.5029 x lo-'
10.632
+ 0.066) x lo-'
0.18953 x lo-'
10.376:
+ 0.056) x lo-‘
0.11300 x 10-1
IO.244
t 0.0401 x 10“
0.7314 x lo-'
10.296;
f 0.0060) x lo-‘
0.88958 x 10-z
f 0.00036l x 1O-a
(-0.356,'
f 0.025) x lo-*
(0.491294I, (-0.36817I‘
?.0.000044) x lo-'
(0.39256,,
f 0.00068) x 10“
-22.075016
0.1329764 x 1O-2 ,-0.191;:, TIb IW)
-0.10697 x lo-' 147.286334
c 0.00039) x 10-a
-0.7363433 x lo-> (0.752
-5.27814
39.865321 k 0.040) x 10-1 t 0.0024, x lo-'
0.15054 x 10-a
0.45131
-0.544976 x lo-'
-1.633798
Note. The quoted errors are one estimated standard deviation. For the spin-rotation constants the convention for the rt( 6) is given in Table I of Ref. (14), and for the hyperfine constants (magnetic and electric quadrupole) we have
mm =; x,,,
%(X) = &(2X& +&A. 180
MILLIMETER
SPECTRUM OF “N’602
181
shown in Fig. 1, each line splits into two groups of MF components, the intensities of which are roughly proportional to ( MF)’ as these lines obey the selection rule given by I+. (2). Consequently the strongest components correspond to M> = M> = + F, for which the Zeeman splitting is the most important. As an example, we give in Table I the Zeeman “doublets” observed for the [J = N’ + 1, F’ = j”‘] c [J” = N” 7 f, F”] components ofthe [N’ = 6, Kh = 1, Kk = 5]* [N” = 6,K: = 0,K’f = 61 rotational transition (the other hyperhne components of this same rotational transition are not significantly affected by the Zeeman effect). We have also evaluated the position of the MF = + F doublets. For this purpose, we used an estimated earth magnetic field of 0.46 G and the Zeeman parameters of Ref. ( 7) as well as the molecular parameters of Ref. (13) and the phase convention and definition of spectroscopic constants of Refs. ( 7, 14, 15). As can be seen in Table I, the observed “doublets” are accurately reproduced by the calculation, showing clearly that the shifts can be accounted for by the Zeeman effect. We have checked that it is also the case for all the AJ = + 1, AF = 0 hyperfme components of the [N, 1, N - l] + [N, 0, N] rotational series observed in the present work. Then using coils in order to compensate for the earth magnetic field, we have observed that the shifts disappeared and the final results given in Table II were obtained under this condition. Most of these newly observed transitions correspond to weak (A J # AF) components which have been assigned using the computed spectrum generated in Ref. ( 13). The agreement between observed and calculated values is excellent and the molecular parameters obtained including this new set of experimental data are given in Table III. They differ only slightly from those of Ref. (13). CONCLUSION
Using a synthetic spectrum of the (000) + (000) band of “N’602 it has been possible to assign easily 111 new weak transitions of this molecule observed by means of microwave spectrometry. ACKNOWLEDGMENTS The authors are indebted to Dr. J. M. Brown for the communication of his least-squares fitting program written for nonsinglet asymmetric rotors with one-nucleus hyperfme interactions. RECEIVED:
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