Collisional quenching of OD A 2Σ+ by H2: experimental and theoretical studies of the state-resolved OD X 2Π product distribution and branching fraction.

We report joint experimental and theoretical studies of outcomes resulting from the nonreactive quenching of electronically excited OD A  (2)Σ(+) by H(2). The experiments utilize a pump-probe technique to detect the OD X  (2)Π product state distribution under single collision conditions. The OD X  (2)Π products are observed primarily in their lowest vibrational state (v(") = 0) with substantially less population in v(") = 1. The OD X  (2)Π products are generated with a high degree of rotational excitation, peaking at N(") = 21 with an average rotational energy of 4600 cm(-1), and a strong propensity for populating the Π(A(')) Λ-doublet component indicative of alignment of the half-filled pπ orbital in the plane of OD rotation. Branching fraction measurements show that the nonreactive channel accounts for less than 20% of quenching outcomes. Complementary classical trajectory calculations of the postquenching dynamics are initiated from representative points along seams of conical intersections between the ground and excited-state potentials of OD(A  (2)Σ(+),X  (2)Π) + H(2). Diabatic modeling of the initial momenta in the dynamical calculations captures the key experimental trends: OD X  (2)Π products released primarily in their ground vibrational state with extensive rotational excitation and a branching ratio that strongly favors reactive quenching. The OD A  (2)Σ(+) + H(2) results are also compared with previous studies on the quenching of OH A  (2)Σ(+) + H(2); the two experimental studies show remarkably similar rotational energy distributions for the OH and OD X  (2)Π radical products.