Barely fluorescent molecules. II. Twin-discharge jet laser-induced fluorescence spectroscopy of HSnBr and DSnBr.

Abstract

HSnBr and DSnBr have been detected for the first time by a combination of laser-induced fluorescence (LIF), fluorescence hole-burning, and wavelength resolved emission spectroscopies. The transient molecules were produced in a twin-discharge jet using separate precursor streams of SnH4/SnD4 and HBr/DBr, both diluted in high pressure argon. The Ã1A″-X̃1A' spectrum of HSnBr only consists of the 00 0 and 20 1 cold bands that show clearly resolved subband structure with fluorescence lifetimes varying from 526 to 162ns. The DSnBr LIF spectrum exhibits four bands (00 0, 20 1, 20 2, and 10 1) whose fluorescence lifetimes decrease from 525ns (00) to 175ns (11). Single vibronic level emission spectra have provided extensive information on the ground state vibrations, including all the anharmonicities and the harmonic frequencies. Fluorescence hole-burning experiments have shown that a few higher HSnBr nonfluorescent levels are very short-lived but still detectable. The ab initio studies of Tarroni and Clouthier [J. Chem. Phys. 156, 064304 (2022)] show that these molecules dissociate into SnBr + H on the excited state potential surface and this is the cause of the short fluorescence lifetimes and breaking off of the LIF spectra. HSnBr is a barely fluorescent molecule in the sense that only vibrational levels less than or equal to 317cm-1 in the excited state emit detectable photons down to the ground state.