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

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 SnH/SnD and HBr/DBr, both diluted in high pressure argon. The ÃA″-X̃A' spectrum of HSnBr only consists of the 0 and 2 cold bands that show clearly resolved subband structure with fluorescence lifetimes varying from 526 to 162 ns. The DSnBr LIF spectrum exhibits four bands (0 , 2 , 2 , and 1 ) whose fluorescence lifetimes decrease from 525 ns (0) to 175 ns (1). 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 317 cm in the excited state emit detectable photons down to the ground state.