Electronic quenching of OH A2Σ+ radicals in collisions with molecular hydrogen

Collisional quenching of electronically excited OH A2Σ+ radicals by molecular hydrogen introduces nonradiative pathways that rapidly remove OH population from the excited state, and result in a significantly decreased fluorescence lifetime. One of these pathways is shown to lead to ground state OH X2Π products with ∼1 eV of internal excitation in both highly excited rotational levels of v = 1 and the lowest rotational levels of v = 2. This highly nonstatistical OH X2Π product distribution reflects the passage of the HO–H2 system through the conical intersection regions that couple the ground and excited state surfaces.