Keiichi Tanaka, Yoshifumi Nakahara, Mitsuhiro Yamaguchi, and Takehiko Tanaka, "CO2-laser-microwave double-resonance spectroscopy of D2CO: precise measurement of the dipole moment in the ground state," J. Opt. Soc. Am. B 4, 1182-1187 (1987)
The method of CO2-laser-microwave double resonance (LMDR) with an intense electric field was used to measure Stark shifts of ground-state microwave transitions of D2CO. Thirty LMDR signals originating from 15 K-doublet transitions were observed, associated with the infrared transitions of the ν4 and ν6 bands. Least-squares analysis of the observed LMDR signals yields precise values of the coefficients in the dipole-moment expansion, μ0 + μJJ(J + 1) + μKK2: μ0, 2.347 134(8) D; μJ, −4.76(10) × 10−6 D; μK, −28.7(18) × 10−6 D; where one-standard-deviation uncertainties are given in parentheses. The infrared–infrared double-resonance signals of PH3, which were calibrated against the OCS dipole moment, were used for the electric-field calibration, allowing us to determine the dipole moment with a precision of 10 parts in 106 (ppm). However, the absolute accuracy of the dipole moment obtained is 50 ppm, as limited by the uncertainty of the OCS dipole moment. The effective dipole moment for the 11,0 ← 11,1 transition measured in the present study agrees well with the effective dipole moment for the 11,0 rotational level from a molecular-beam electric resonance experiment. The μJ and μK coefficients calculated from Watson’s θγαβ constants agree well with the experimental values.
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K-doublet transition obeying the ΔM = 0 selection rule.
Uncertainty is estimated to be 10 kHz.
Stark shift of the microwave transition, defined as the transition frequency calculated at the indicated electric field minus that calculated at zero field.
O–C (MHz) is the observed frequency minus the transition frequency calculated at the indicated electric field. O–C (V/mm) = −O–C (MHz)/(∂ν/∂E), where (∂ν/∂E) is the Stark coefficient for the microwave transition in MHz/(V/mm).
Infrared transitions in the ν4 and ν6 bands used for pumping. The quantum number M in the ground state is the same as that for the microwave transition and changes by ΔM in the transition.
CO2-laser lines are indicated by the P(J) or R(J) symbol with a number attached in front of it; the numbers 1 and 2 indicate the 10.6- and the 9.4-μm normal CO2 laser, respectively; 3 indicates the 10.3-μm C18O2 laser; 5 and 6 the 10.9- and the 9.8-μm 13CO2 lasers, respectively; and 7 the 10.8-μm 13C18O2 laser.
Weighted zero in the analysis.
Table 2
Electric Properties of D2CO in the Ground State from LMDRa
One-standard-deviation uncertainty to be attached to the last digit is given in parentheses.
The electric field was calibrated assuming the OCS dipole moment in the 0110 state as 0.70433(3) D.26 The absolute accuracy of the dipole moment is 50 ppm, as determined by the uncertainty of the OCS dipole moment.
Fixed at zero in the analysis.
Fixed at the calculated values in the analysis.
K-doublet transition obeying the ΔM = 0 selection rule.
Uncertainty is estimated to be 10 kHz.
Stark shift of the microwave transition, defined as the transition frequency calculated at the indicated electric field minus that calculated at zero field.
O–C (MHz) is the observed frequency minus the transition frequency calculated at the indicated electric field. O–C (V/mm) = −O–C (MHz)/(∂ν/∂E), where (∂ν/∂E) is the Stark coefficient for the microwave transition in MHz/(V/mm).
Infrared transitions in the ν4 and ν6 bands used for pumping. The quantum number M in the ground state is the same as that for the microwave transition and changes by ΔM in the transition.
CO2-laser lines are indicated by the P(J) or R(J) symbol with a number attached in front of it; the numbers 1 and 2 indicate the 10.6- and the 9.4-μm normal CO2 laser, respectively; 3 indicates the 10.3-μm C18O2 laser; 5 and 6 the 10.9- and the 9.8-μm 13CO2 lasers, respectively; and 7 the 10.8-μm 13C18O2 laser.
Weighted zero in the analysis.
Table 2
Electric Properties of D2CO in the Ground State from LMDRa
One-standard-deviation uncertainty to be attached to the last digit is given in parentheses.
The electric field was calibrated assuming the OCS dipole moment in the 0110 state as 0.70433(3) D.26 The absolute accuracy of the dipole moment is 50 ppm, as determined by the uncertainty of the OCS dipole moment.
Fixed at zero in the analysis.
Fixed at the calculated values in the analysis.
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