Predissociation of the B Σu-3 state of S2: A coupled-channel model.

A coupled-channel Schrödinger equation model of predissociation in the B Σu-3 state of S2 is developed and optimized by comparison with recent photoabsorption spectra of the B Σu-3-X Σg-3(v,0) bands for 11 ≤ v ≤ 27, covering the energy range 35 800-41 500 cm-1. All bands in this range exhibit varying degrees of diffuseness, with corresponding predissociation linewidths Γ ≈ 4-60 cm-1 full-width at half-maximum. Model comparisons with both low-temperature (T = 370 K) and high-temperature (T = 823 K) spectra indicate, for many bands, significant dependence of the linewidth on both the rotational quantum number J and the fine-structure component Fi. Just as in the analogous case of O2, the B(v)-state predissociation in S2 is caused principally by spin-orbit interaction with 3Πu, 1Πu, 5Πu, and Σu+3 states. The inner-limb crossing with B″3Πu is responsible for the predissociation of B(v = 11) and provides a significant slowly varying contribution for B(v ≥ 12). The outer crossings with the 1Πu, 5Πu, and 2 Σu+3 states are responsible for oscillatory contributions to the predissociation widths, with first peaks at v = 13, 20, and 24, respectively, and the 5Πu contribution dominant. Prior to the photodissociation imaging study of Frederix et al. [J. Phys. Chem. A 113, 14995 (2009)], which redefined the dissociation energy of S2, the prevailing paradigm was that only the 1Πu interaction was responsible for the B(v = 11-16) predissociation: this view is not supported by our model.