CO₂ and CO laser microwave double resonance spectroscopy of OCS: Precise measurement of dipole moment and polarizability anisotropy

Laser-microwave double resonance (LMDR) with high electric field was applied to the OCS molecule. Stark Lamb-dip spectra due to the infrared transitions of the 2ν₂(02⁰0-00⁰0, 9.6 μm), 2ν₁(20⁰0-00⁰0, 5.8μm), and ν₁+2ν₂(12⁰0-00⁰0, 5.3μm) bands were observed with the CO₂ and CO lasers. The spectra due to the corresponding hot bands; 03¹0-01¹0, 04 ⁰0-02⁰0, 12⁰0-10⁰0, 13 ¹0-11¹0; 21¹0-01¹0, 30 ⁰0-10⁰0; 14⁰0-02⁰0, 14 ²0-02²0, 15¹0-03¹0, 22 ⁰0-10⁰0; and a few bands of OC³⁴S and O ¹³CS were also identified. Associated with these infrared transitions, more than 90 LMDR signals were detected and assigned to rotational transitions in the 11 vibrational states 00⁰0, 10⁰0, 20⁰0, 01¹0, 02⁰0, 02²0, 03 ¹0, 04⁰0, 12⁰0, 14²0, and 22 ⁰0 of the normal species, and in the two vibrational states 00 ⁰0 and 02⁰0 of both OC³⁴S and O¹³CS. Dipole moments were determined with accuracies (2.5σ) better than 2×10^-5 D for all these vibrational states. Polarizability anisotropies were also obtained for some states. The data for the ground ν₁ and ν₂ vibrational states are, with the 2.5σ uncertainties in parentheses. Ground ν₁ ν₂ μ 0.715 196(10) 0.694 413(5) 0.704 330(11) D δμ ... -0.020 783(11) -0.010 866(15) D α 4.67(11) 4.84(14) 4.85(30) Å3 From the Stark Lamb-dip spectra the origins of various vibrational bands were determined, among which those for the 02⁰0-00⁰0 and 03¹0-01¹0 bands are 31 389 530.4(25) and 31 566 477.57(67) MHz, respectively. The dipole moments and band origins obtained in the present study agree well with the available accurate values from molecular beam electric resonance and heterodyne measurement, respectively. A procedure for the calibration of electric field in laser Stark and double resonance spectroscopy, in which the dipole moment of OCS is used as the standard, is described.