Vibrational energy levels and predissociation lifetimes of the A²Σ⁺ state of SH/SD radicals by photodissociation spectroscopy

Photo-predissociation of SH and SD radicals in the A²Σ⁺ state is investigated using the high-n Rydberg atom time-of-flight (HRTOF) technique. By measuring the photoproduct translational energy distributions as a function of excitation wavelength, contributions from overlapping A²Σ⁺ (v') <!--[if gte msEquation 12]>? X²Π (v") transitions can be separated, and the H/D + S(³P_J) photofragment yield (PFY) spectra are obtained across various rovibrational levels (SH v' = 0-7 and SD v' = 0-8) of the A²Σ⁺ <!--[if gte msEquation 12]> style='font-size:12.0pt;mso-bidi-font-size:11.0pt;line-height:107%;font-family:
"Cambria Math",serif;mso-fareast-font-family:DengXian;mso-fareast-theme-font:
minor-fareast;mso-bidi-font-family:"Times New Roman";mso-ansi-language:EN-US;
mso-fareast-language:ZH-CN;mso-bidi-language:AR-SA'>? X²Π bands. The upper A²Σ⁺ state vibrational levels v' = 5-7 of SH and v' = 3-8 of SD are determined for the first time. The PFY spectra are analyzed with the simulation program PGOPHER [C. M. Western, J. Quant. Spectrosc. Radiat. Transfer, 186, 221 (2016)], which gives vibrational origins and linewidths of the rovibrational levels of the A²Σ⁺ state. The linewidths (≥ 1.5 cm⁻¹) of the SH A²Σ⁺ v' = 3-7 and SD A²Σ⁺ v' = 2-8 states are characterized for the first time in this work, demonstrating that these levels undergo rapid predissociation with lifetimes on the order of picosecond. The lifetimes of the SD A²Σ⁺ v' = 0, N' = 1 and 2 levels are determined to be 247±50 ns and 176±60 ns by pump-probe delay measurements, respectively. The experimentally measured lifetimes are in a reasonable agreement with the theoretical predictions.