High-resolution Fourier transform emission spectroscopy of the A∼2Πi−X∼2Πi band of the OCS⁺ ion

High resolution Fourier transform emission spectroscopy of the A∼2Πi-X∼2Πi band of the OCS⁺ ion was performed in the UV region to observe the ν1 (CO stretch) progression bands (υ₁ = 0 → 2-5) for both the Ω=3/2 and 1/2 spin components. Accurate molecular constants including the rotational constants, B₀ = 0.194 765(13) and 0.187 106(13) cm⁻¹, and the spin-orbit interaction constants, A₀ = −381.0(56) and −126.5(56) cm⁻¹, were determined for the X∼2Π and A∼2Π states, respectively, by the simultaneous analysis of the observed progression bands. The CO bond length (r_CO = 1.2810 Å) for the A∼2Π state, derived from the rotational constant B₀ and Franck-Condon factors, is longer by 0.1756 Å than that (1.1054 Å) for the X∼2Π state, while the CS bond length for the A∼2Π state is shorter by 0.0905 Å than that for the X∼2Π state. Pure rotational transition frequencies in the ground X∼2Π state are predicted, as well as transition frequencies of the ν1 fundamental band, with the present molecular constants.