15min:

SHENG-GUI HE, DAVID A. HOSTUTLER AND DENNIS J. CLOUTHIER, Department of Chemistry, University of Kentucky, Lexington, KY 40506-0055.

The previously observed 418 - 402 nm LIF spectra of the jet-cooled HCCSe and DCCSe free radicals have been vibrationally and rotationally analyzed as a ² _i - ² _i electronic transition. The upper electronic state has a very large HCC bending mode Renner-Teller effect although the CCSe bend is nearly harmonic, in accord with our analysis of the electronic spectra of the HCCS and DCCS radicals, which are found to be quasi-linear in the excited state. Based on ab initio calculations, the ground state vibrational energy levels obtained from wave-length resolved emission spectra have also been assigned for both HCCSe and DCCSe. The LIF and emission spectra of HCCSe/DCCSe are not as complex as those of HCCS/DCCS because the selenium-containing radicals have a very large spin-orbit splitting which decreases the Renner-Teller complications. HCCSe exhibits field-free molecular quantum beats in collision-free single rotational level fluorescence decays due to coupling with high vibrational levels of the ground state.