Predissociation of the B Σ u - 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 F_i. Just as in the analogous case of O₂, the B(v)-state predissociation in S₂ is caused principally by spin-orbit interaction with ³Π_u, ¹Π_u, ⁵Π_u, and Σu+3 states. The inner-limb crossing with B^″3Π_u 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 ¹Π_u, ⁵Π_u, 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 ⁵Π_u 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 ¹Π_u interaction was responsible for the B(v = 11-16) predissociation: this view is not supported by our model.