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Submillimeter wave spectrum of 17O2
Volume 113, number 5
CHEMICAL PHYSICS LETTERS
1
Fc%marj 1985
SUBMILLIMETERWAVESPECTRUMOF"02 G. CAZZOLI and C. DEGLI ESPGSTI Centro distudio di Spdfrorwpio a Microonde, Universitb di Bologna, Via Selmi 2, 40126 BologIla, Italy and Istituto di Spettrvswpm Molewlare de1 CNR. Via de’ Cartagnoli 1. 40126 Bologna. Italy Received 14 September 1984, in tinal form 15 November 1984
The measurement of the AN= 2 rotational Iotalional
constants
of this molecule.
allowed us to determine more accurate values of the transitions of “02 = -0.132(l). The new values (in MHz) are: Bo = 40561_35(1);Oe
Recently the microwave spectrum of 170, in the range 56-64 GHz has been observed and analysed [l] In that region the only transitions that can be observed are those with Ahr = 0 so that the rotational constant B. and the centrifugal distortion constant Do cannot be determined simultaneously. As pointed out in ref. [l], observation of the m = 2 transitions requires qtute a good sensitivity in the submrllimeter wave region because of the fine and hyperfme structure of the spectrum due to the pres ence in the molecule of two unpaired electrons and of two nuclei with a nuclear spin of 5/2 [l] _ Recently an indium antimonide photoconducting detector working at 1.6 K has been assembled in our laboratory. This detector allowed us to improve the sensitivity of our spectrometer by about one order of magnitude compared to that obtained with a silicon diode detector. The combined use of this InSb detector and of a computer-controlled microwave source, which also performs the averagmg and the smoothing of the digitized spectra, gave us the first observation of the microwave spectrum of oxygen in the a ‘a8 state [2]. The same spectrometer has been used to observe the submillimeter wave spectrum of 1702 with the following modification: A K band brass waveguide 30 cm long has been
Zeeman modulation at 16.6 kHz and detection at 33.3 kHz has been employed in order to observe the second derivative of the actual lineshape and to sup press the spurious background signal Four transrtions of 170, have been observed and
used as the absorption cell. This cell was cooled at liquid-nitrogen temperature to increase the population of the levels with small values of the quantum number A!
Fig. 1. The 6,4,2,3-6,4,&l trarw-ion of”02. Scan from 400997 to 401007 MHz. marker evff~ 1.0 MHz. time mn stant 3 s. The spectrum is the accum&tion of il SQX The heavy and light traces refer to the smoothed and to the actual spectrum respectively
0 009-2614/85/s (North-Holland
03.30 0 Elsevier Science Publishers B.V. Physrcs Publishmg Divrsion)
one of these is shown in fig 1 to give a feeling for the srgnal-to-noise ratio. The transrtion frequencies and
in,
501
Volume
113, number 5
CHEMICAL
J’
6512 4 3 2 1 6 4
1 1 2
F” 1” J" N"
Ohs.
Obr
6 4 2 6
233898.37 233609.40 233319.78 401002 39
-0
2 2 3
1 1 1 2
0 0 0 1
-
talc
026 0.161 -0.145 0.002
BO
Do ha AD YO
7D
the assigned quantum numbers are in table 1. The values of the new measured line frequencies
; x
together with those already measured [l] were the input data of the computer program described in ref. [l] . This program gives a least-squares fit to the molecular parameters of the Hamiltonian [3] :
standard dcviatmn
H = H(rfs) + H(hfs), where + %Ao(3SZ -
= BON2
-
D,A+
+ ; hD((3SZ
-
SQ, iv2) + _: @J-S
H(rfs)
H(hfs)
= al-S
+ [d4I(U
+ P (31,S, -
572) + ; y&V-S,
N2),
- 1-S)
l)] (31; -
-1 February 1985
Molecular parametersof l’O1
in MHz
N’ c
5 3 1 4
LETTERS
Table 2
Table 1 Observed transition frequencies of “02 F’ 1’
PHYSICS
r2>
3
in MHz a)
Thfi work
Ref. [l]
40561.35(l) -0 132(l) 59498.883(5) O-05479(3) -237.6527(15) -0.000218(3) -54.758(3) 46.679(3) -8.29(5)
40561.37(4) -0_138(fiied) 59498.879(5) 0.05479(3) -237 6462(S) -0.000217(1) -54.75%(3) 46.679(3) -8.29(5)
of the fit 0.07
MHz
Standard errors arc given in parentheses in the last digit quoted.
value is outside the standard error limits compared to that previously obtained. This discrepancy is due to the correlation between Do and y. as can be verified by performing a series of fits keeping Do fared at different values. The values of the hyperfine magnetic coupling constants are very near to those prevrously obtained for 160-170 and 170-‘80 [4,5], so that the con-
clusions on the electronic structure of 0, derived by Miller et al. [6] are confirmed by our measurements.
The results of the fit are shown in table 2 together with those previously obtained_ As expected, the introduction in the calculations of the A/V = 2 transi-
References
tion frequencies allows the determination of the centrifugal distortion constant Do, previously constrained to the calculated value of -0.138 MHz, and an improved value of B.
G. Cazzoh_ C Degli Cimento 3D (1984) [2] G caVolj_ C. Degli Letters 100 (1983)
All the fme and hyperfine structure parameters except y. are unchanged compared to those already obtained, since they can be determined from the AN = 0 transitions As far as y,-, IS concerned the newly determined
(W&y. New York 1975). 141 S I_ MiUcr and CH Townes, Phys Rev. 4 (1953) 537 (51 G. Cazzoli, C De@ Esposti, P-G. Favero and G. Scvcri_ Nuovo Cimento B 62 (1981) 243. (61 S-L. Miller, CH_ Townes and M_ Kotnni, Phys Rev. 90 (1953) 542.
502
[l]
Esposti and B.M. Landsberg, Nuovo 341. Esposti and P G Favcro, Chem Phyr 99.
[3] M Mizushuna,The theory of rotating diatomic molecules
CHEMICAL PHYSICS LETTERS
1
Fc%marj 1985
SUBMILLIMETERWAVESPECTRUMOF"02 G. CAZZOLI and C. DEGLI ESPGSTI Centro distudio di Spdfrorwpio a Microonde, Universitb di Bologna, Via Selmi 2, 40126 BologIla, Italy and Istituto di Spettrvswpm Molewlare de1 CNR. Via de’ Cartagnoli 1. 40126 Bologna. Italy Received 14 September 1984, in tinal form 15 November 1984
The measurement of the AN= 2 rotational Iotalional
constants
of this molecule.
allowed us to determine more accurate values of the transitions of “02 = -0.132(l). The new values (in MHz) are: Bo = 40561_35(1);Oe
Recently the microwave spectrum of 170, in the range 56-64 GHz has been observed and analysed [l] In that region the only transitions that can be observed are those with Ahr = 0 so that the rotational constant B. and the centrifugal distortion constant Do cannot be determined simultaneously. As pointed out in ref. [l], observation of the m = 2 transitions requires qtute a good sensitivity in the submrllimeter wave region because of the fine and hyperfme structure of the spectrum due to the pres ence in the molecule of two unpaired electrons and of two nuclei with a nuclear spin of 5/2 [l] _ Recently an indium antimonide photoconducting detector working at 1.6 K has been assembled in our laboratory. This detector allowed us to improve the sensitivity of our spectrometer by about one order of magnitude compared to that obtained with a silicon diode detector. The combined use of this InSb detector and of a computer-controlled microwave source, which also performs the averagmg and the smoothing of the digitized spectra, gave us the first observation of the microwave spectrum of oxygen in the a ‘a8 state [2]. The same spectrometer has been used to observe the submillimeter wave spectrum of 1702 with the following modification: A K band brass waveguide 30 cm long has been
Zeeman modulation at 16.6 kHz and detection at 33.3 kHz has been employed in order to observe the second derivative of the actual lineshape and to sup press the spurious background signal Four transrtions of 170, have been observed and
used as the absorption cell. This cell was cooled at liquid-nitrogen temperature to increase the population of the levels with small values of the quantum number A!
Fig. 1. The 6,4,2,3-6,4,&l trarw-ion of”02. Scan from 400997 to 401007 MHz. marker evff~ 1.0 MHz. time mn stant 3 s. The spectrum is the accum&tion of il SQX The heavy and light traces refer to the smoothed and to the actual spectrum respectively
0 009-2614/85/s (North-Holland
03.30 0 Elsevier Science Publishers B.V. Physrcs Publishmg Divrsion)
one of these is shown in fig 1 to give a feeling for the srgnal-to-noise ratio. The transrtion frequencies and
in,
501
Volume
113, number 5
CHEMICAL
J’
6512 4 3 2 1 6 4
1 1 2
F” 1” J" N"
Ohs.
Obr
6 4 2 6
233898.37 233609.40 233319.78 401002 39
-0
2 2 3
1 1 1 2
0 0 0 1
-
talc
026 0.161 -0.145 0.002
BO
Do ha AD YO
7D
the assigned quantum numbers are in table 1. The values of the new measured line frequencies
; x
together with those already measured [l] were the input data of the computer program described in ref. [l] . This program gives a least-squares fit to the molecular parameters of the Hamiltonian [3] :
standard dcviatmn
H = H(rfs) + H(hfs), where + %Ao(3SZ -
= BON2
-
D,A+
+ ; hD((3SZ
-
SQ, iv2) + _: @J-S
H(rfs)
H(hfs)
= al-S
+ [d4I(U
+ P (31,S, -
572) + ; y&V-S,
N2),
- 1-S)
l)] (31; -
-1 February 1985
Molecular parametersof l’O1
in MHz
N’ c
5 3 1 4
LETTERS
Table 2
Table 1 Observed transition frequencies of “02 F’ 1’
PHYSICS
r2>
3
in MHz a)
Thfi work
Ref. [l]
40561.35(l) -0 132(l) 59498.883(5) O-05479(3) -237.6527(15) -0.000218(3) -54.758(3) 46.679(3) -8.29(5)
40561.37(4) -0_138(fiied) 59498.879(5) 0.05479(3) -237 6462(S) -0.000217(1) -54.75%(3) 46.679(3) -8.29(5)
of the fit 0.07
MHz
Standard errors arc given in parentheses in the last digit quoted.
value is outside the standard error limits compared to that previously obtained. This discrepancy is due to the correlation between Do and y. as can be verified by performing a series of fits keeping Do fared at different values. The values of the hyperfine magnetic coupling constants are very near to those prevrously obtained for 160-170 and 170-‘80 [4,5], so that the con-
clusions on the electronic structure of 0, derived by Miller et al. [6] are confirmed by our measurements.
The results of the fit are shown in table 2 together with those previously obtained_ As expected, the introduction in the calculations of the A/V = 2 transi-
References
tion frequencies allows the determination of the centrifugal distortion constant Do, previously constrained to the calculated value of -0.138 MHz, and an improved value of B.
G. Cazzoh_ C Degli Cimento 3D (1984) [2] G caVolj_ C. Degli Letters 100 (1983)
All the fme and hyperfine structure parameters except y. are unchanged compared to those already obtained, since they can be determined from the AN = 0 transitions As far as y,-, IS concerned the newly determined
(W&y. New York 1975). 141 S I_ MiUcr and CH Townes, Phys Rev. 4 (1953) 537 (51 G. Cazzoli, C De@ Esposti, P-G. Favero and G. Scvcri_ Nuovo Cimento B 62 (1981) 243. (61 S-L. Miller, CH_ Townes and M_ Kotnni, Phys Rev. 90 (1953) 542.
502
[l]
Esposti and B.M. Landsberg, Nuovo 341. Esposti and P G Favcro, Chem Phyr 99.
[3] M Mizushuna,The theory of rotating diatomic molecules