A comparative high-resolution study of predissociation linewidths in the Schumann-Runge bands of O₂

Results are presented of a comparative study in which three distinct high-resolution experimental techniques (vacuum-ultraviolet laser spectroscopy, laser-induced fluorescence spectroscopy and vacuum-ultraviolet Fourier-transform spectroscopy) were used to study predissociation in the Schumann-Runge bands of O₂ B³Σ_u^-(v^′)←X ³Σ_g^-(v^″) with v^′=13 and 14. Our measurements are the first to be performed at high resolution for these levels and represent a significant advance on previous knowledge, characterizing completely the fine-structure and rotation dependencies of the B³Σ_u^-(v=13 and 14)-state predissociation for the first time. The measured fine-structurespecific linewidths will result in significant improvements in the parameterization of models describing predissociation of the B-state and will have an impact on the development of realistic photochemical models of the terrestrial atmosphere. Good agreement was found between linewidths measured using vacuum-ultraviolet laser spectroscopy and laser-induced fluorescence spectroscopy, but unexpected difficulties arose in determining quantitative linewidths using vacuum-ultraviolet Fourier-transform spectroscopy. For each experimental technique, the instrumental resolution had to be carefully controlled and monitored in order to ensure reliable interpretation of the measured spectra.