CO₂ laser Stark spectroscopy of the ν₄ band of SiHF₃: The C₀ rotational constant and vibrationally induced dipole moment

The ν₄ (SiF₃ degenerate stretch) fundamental band of SiHF₃ has been investigated by the CO₂ laser Stark spectroscopy. The vibrationally induced dipole moment was found to give remarkable perturbations of the type (Δl,ΔK) = (2, - 1) in the ν₄ vibrational state under intense electric field. Several perturbation-induced rovibrational transitions obeying the Δ(K - l) = ±3 selection rules were observed in the Stark spectrum. The C₀ rotational constant, which is otherwise hard to obtain for a symmetric top molecule, was determined to be 4134.73(71) MHz. The vibrationally induced dipole moment μ, in the ν₄ state was derived as ±0.034 38(17) D, the sign being experimentally indeterminable. The band origin, the Coriolis constant Cζ₄, and the vibration-rotation constant α₄^care 999.581 076(30) cm^-1, 2445.59(71) MHz, and 9.243(22) MHz, respectively. The dipole moment is 1.359 20(22) D in the ground state, and increases by 0.026 73(10) D on excitation of the ν₄ vibration. The uncertainties given in the parentheses correspond to three standard deviations. The present results are compared with our previous results of a similar analysis for the deuterated species. The dipole moment in the ground vibrational state decreases by 0.002 01(28) D on deuteration. The vibrationally induced dipole moments μ, and the vibrational changes δμ₄ of the dipole moment for both isotropic species are discussed theoretically. We introduce the coefficient of the mean square amplitude dependence for the bond moment, which is useful in the discussion.