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The pure rotation spectrum of a1Δg O2
JOURNAL
OF
MOLECULAR
SPECT’ROSCOPY
109,205-206 (1985)
The Pure Rotation Spectrum of a’$
O2
Recently, Scalabrin et al. (I) reported the laser magnetic resonance spectra of several rotational transitions of the metastable a’ Ar state of the oxygen molecule. This note reports the zero-field rotational spectrum of a’$ Or below 900 GHz. The spectrum was observed by passing harmonics of millimeter-wave klystrons down the length of a I .3-m, 100-I 50 mA dc glow discharge through approximately 120 mTorr pure Or. The submillimeter spectrometer has been described previously (2), and was used with tone-burst modulation. The J = 3 - 2 to the J = 10 - 9 transitions have all been measured. These measurements are given in Table I along with their differences from frequencies calculated with the parameters given in Table II. These parameters are defined in a manner consistent with Ref. (I), so that the frequencies are given by IQ - J - 1) = 2(& + SD&J - 4&J’
+ (- l)‘qJ’(J’ - I).
A weighted least-squares fit has been used to determine the parameters. Although Scalabrin et al. expressed some slight dissatisfaction with the quality of their fit, and while there are some small differences between the measurements given here and theirs. the more precise new values of the parameters are ah well within the uncertainties given in Ref. (I). The uncertainty of the A doubling constant, q, is 26 times smaller than that which was obtained from the LMR work, and places a significantly more stringent constraint on its magnitude. In spite of this, it should IX noted that the value of q = 0 is within two standard errors of the value derived here. Thus, one cannot say with a very high degree of confidence that q is large enough to have been determined by even an experiment of this precision. The sextic centrifugal constant, H, is not determinable from these data, but is not correlated with q,and does not appreciably change the derived value or the uncertainty of q.
TABLE I Observed Rotational Transitions of a’4 O2 (in MHz) J’_
Observed
J”
( a)
frequency
Obs.talc.
255017.937(30)
-0.008
4-3
340006.779(20)
-0.015
5-4
424980.983(20)
6-5
509936.752(20)
7-6
594870.607(40)
0.035
8-l
679778.668(40)
0.040
3-2
9-8 10
-
9
0.018 -0.015
764657.384(40)
-0.021
849502.992(40)
-0.009 RMS= 0.023
a.
The
numbers
in
parentheses
are
205
experimental
uncertainties.
0022-2852185 $3.00 Copyright
@ 1985 by Academic Press, Inc.
All righU of reproduction in any form mrvcd.
206
NOTES TABLE
II
Molecular Parameters Parameter
Value
B,/MHz
42504.5203(17)
D,/kHz
152.957(15)
q /Hz
-5.4(34)
Numbers
in parentheses
are
standard
errors.
Because of its small size, q is not easily determined from the spectrum of ‘60’60 for which only half of the levels are allowed. Measurements of splittings with high J, high-resolution studies of ‘60’80 will probably provide the best determination of this constant. In conclusion, a set of precisely measured zero-field transitions of a’$ O2 have been presented. These have improved the precision of the previously determined constants and. in addition, may provide convenient references for determination of submillimeter laser frequencies. ACKNOWLEDGMENT The research described in this paper was performed by the Jet Propulsion Laboratory, California Institute of Technology. under contract with the National Aeronautics and Space Administration. REFERENCES 1.
A.
SCALABRIN,
R. J.
SAYKALLY,
Spectrosc. 89, 344-35 2. H. M. Pmc~rr
AND
K. M. EVENSON,H. E. RADFORD,AND M. MIZUSHIMA,J. Mol.
1 (1981).
T. L.
BOYD, J. Mol. Spectrosc.
75, 53-57 (1979). KURT W. HILLIG II’ W. CHIL? WILLIAM G. READ* E. A. COHEN
CINDY C.
Jet Propulsion Laboralory California Institute of Technology Pasadena, Calijornia 91109 Received September 1 I, I984
’ NASA/ASEE Summer Faculty Fellow. Permanent address: Department of Chemistry, University of Michigan, Ann Arbor, Mich. 48109. * NASA/NRC Resident Research Associate.
OF
MOLECULAR
SPECT’ROSCOPY
109,205-206 (1985)
The Pure Rotation Spectrum of a’$
O2
Recently, Scalabrin et al. (I) reported the laser magnetic resonance spectra of several rotational transitions of the metastable a’ Ar state of the oxygen molecule. This note reports the zero-field rotational spectrum of a’$ Or below 900 GHz. The spectrum was observed by passing harmonics of millimeter-wave klystrons down the length of a I .3-m, 100-I 50 mA dc glow discharge through approximately 120 mTorr pure Or. The submillimeter spectrometer has been described previously (2), and was used with tone-burst modulation. The J = 3 - 2 to the J = 10 - 9 transitions have all been measured. These measurements are given in Table I along with their differences from frequencies calculated with the parameters given in Table II. These parameters are defined in a manner consistent with Ref. (I), so that the frequencies are given by IQ - J - 1) = 2(& + SD&J - 4&J’
+ (- l)‘qJ’(J’ - I).
A weighted least-squares fit has been used to determine the parameters. Although Scalabrin et al. expressed some slight dissatisfaction with the quality of their fit, and while there are some small differences between the measurements given here and theirs. the more precise new values of the parameters are ah well within the uncertainties given in Ref. (I). The uncertainty of the A doubling constant, q, is 26 times smaller than that which was obtained from the LMR work, and places a significantly more stringent constraint on its magnitude. In spite of this, it should IX noted that the value of q = 0 is within two standard errors of the value derived here. Thus, one cannot say with a very high degree of confidence that q is large enough to have been determined by even an experiment of this precision. The sextic centrifugal constant, H, is not determinable from these data, but is not correlated with q,and does not appreciably change the derived value or the uncertainty of q.
TABLE I Observed Rotational Transitions of a’4 O2 (in MHz) J’_
Observed
J”
( a)
frequency
Obs.talc.
255017.937(30)
-0.008
4-3
340006.779(20)
-0.015
5-4
424980.983(20)
6-5
509936.752(20)
7-6
594870.607(40)
0.035
8-l
679778.668(40)
0.040
3-2
9-8 10
-
9
0.018 -0.015
764657.384(40)
-0.021
849502.992(40)
-0.009 RMS= 0.023
a.
The
numbers
in
parentheses
are
205
experimental
uncertainties.
0022-2852185 $3.00 Copyright
@ 1985 by Academic Press, Inc.
All righU of reproduction in any form mrvcd.
206
NOTES TABLE
II
Molecular Parameters Parameter
Value
B,/MHz
42504.5203(17)
D,/kHz
152.957(15)
q /Hz
-5.4(34)
Numbers
in parentheses
are
standard
errors.
Because of its small size, q is not easily determined from the spectrum of ‘60’60 for which only half of the levels are allowed. Measurements of splittings with high J, high-resolution studies of ‘60’80 will probably provide the best determination of this constant. In conclusion, a set of precisely measured zero-field transitions of a’$ O2 have been presented. These have improved the precision of the previously determined constants and. in addition, may provide convenient references for determination of submillimeter laser frequencies. ACKNOWLEDGMENT The research described in this paper was performed by the Jet Propulsion Laboratory, California Institute of Technology. under contract with the National Aeronautics and Space Administration. REFERENCES 1.
A.
SCALABRIN,
R. J.
SAYKALLY,
Spectrosc. 89, 344-35 2. H. M. Pmc~rr
AND
K. M. EVENSON,H. E. RADFORD,AND M. MIZUSHIMA,J. Mol.
1 (1981).
T. L.
BOYD, J. Mol. Spectrosc.
75, 53-57 (1979). KURT W. HILLIG II’ W. CHIL? WILLIAM G. READ* E. A. COHEN
CINDY C.
Jet Propulsion Laboralory California Institute of Technology Pasadena, Calijornia 91109 Received September 1 I, I984
’ NASA/ASEE Summer Faculty Fellow. Permanent address: Department of Chemistry, University of Michigan, Ann Arbor, Mich. 48109. * NASA/NRC Resident Research Associate.