Ultraviolet photoabsorption in the $B\,{}^3Σ^- - X\,{}^3Σ^-$ and $C\,{}^3Π - X\,{}^3Σ^-$ band systems of SO sulphur isotopologues

Abstract

High-resolution far-ultraviolet broadband Fourier-transform photoabsorption spectra of 32 S 16 O, 33 S 16 O, 34 S 16 O, and 36 S 16 O are recorded in a microwave discharge seeded with SO 2bands are observed or inferred in the 43 000 to 51 000 cm −1 (196 to 233 nm) spectral range. This is the first experimental detection of a C 3 Π(v > 2) level and of any of these observed bands in an S-substituted isotopologue. Additional measurements of A 3 Π(v = 1 − 3) ← X 3 Σ − (v = 0) provide a calibration of the SO column density. Measured band profiles are fitted to an effective-Hamiltonian model of coupled excited B 3 Σ − and C 3 Π states along with their predissociation linewidths and absorption band strengths. Electronic-state potential-energy curves and transition moments are deduced. The end result is a list of line frequencies, f -values, and dissociation widths describing the far-ultraviolet photodissociation spectrum of SO that is accurate enough for computing atmospheric photolytic isotope-fractionation.