Analysis of high-resolution infrared and CARS spectra of 34S 18O 3

Abstract

Three fundamental modes and several hot bands of 34S 18O 3 have been investigated using both infrared spectroscopy and coherent anti-Stokes Raman scattering spectroscopy (CARS). Coriolis coupling effects are particularly noticeable in 34S 18O 3 due to the close proximity of the ν 2 and ν 4 fundamental vibrations, whose wavenumber values are 477.50864(5) and 502.05565(4) cm −1. The uncertainties in the last digits are shown in parentheses and are two standard deviations. Hot band transitions from ν 2, ν 4 levels give access to infrared inactive ν 2, ν 4 combination/overtone levels which interact strongly with levels of the Raman-active ν 1 symmetric stretching mode due to indirect Coriolis couplings, l-resonances, and Fermi resonances. The result is a complex ν 1 CARS Q-branch spectrum that is the most perturbed of the four SO 3 isotopomers we have studied. The relative importance of these interaction terms on the ν 1 CARS spectrum is examined in some detail and accurate rovibrational constants are determined for all of the mixed states, leading to deperturbed values of 1004.662(24), 0.0003503(9), and 0.0007066(12) cm −1 for ν 1, α 1 B , and α 1 C , respectively. The B e value is found to be 0.310875(12) cm −1, which gives an equilibrium bond length r e of 141.7339(3) pm, in excellent agreement with values of 141.7340(1) and 141.7347(7) pm reported earlier for 32S 16O 3 and 34S 16O 3.