A study of the molecular structure and renner-teller effect in the A~2PI_u - X~2PI_g electronic spectrum of jet-cooled boron disulfide, BS_2

摘要

The A~2PI_u-X~2PI_g electronic band system of jet-cooled boron disulfide (BS_2) has been recorded in the 760-530 nm region by laser-induced fluorescence (LIF) and wavelength resolved emission techniques. The free radical was produced in a pulsed electric discharge jet using a precursor mixture of BCl_3 and CS-2 in argon. The LIF spectrum consists of a long progression of strong bands involving the upsilon'_1 (B-S stretching) mode and combinations involving wupsilon'_2 and 2upsilon'_3, as well many hot band built on the 2_1~1 band. Detailed analysis of the spectrum shows that the ground state exhibits a substantial Renner-Teller effect with epsilon = -0.2012 and a spin-orbit coupling constant of A =-413.80 cm~(-1). Angular momentum coupling is negligible in the excited state, which has a much smaller spin-orbit coupling constant of A = -259.15 cm~(-1). The vibrational frequencies of ~(11)BS_2 are omega"_1 = 542.8, omega"_2 = 285.0, omega"_3 = 1010.5, omega'_1 = 514.1, omega'_2 = 309.7, and omega'_3 = 1543.6 cm~(-1). Rotational analysis of the 0_0~0 band allowed a determination of the effective molecular structures as r"_0 (BS) = 1.6648(4) A and r'_0 (BS) = 1.7127(5) A. Ab initio methods have been used to predict the BS_2 spectroscopic parameters and good agreement with experiment was found. Our present understanding of the LIF spectrum is in accord with the pioneering analysis of the absorption spectrum of matrix isolated BS_2 published by Brom and Weltner [J.Mol.Spectrosc. 45, 82 (1973)] three decades ago.