State-resolved distribution of OH X ~2Пproducts arising from electronicquenching of OH A ~2Σ+byN_2

摘要

The nascent OH X ~2Пproduct state distribution arising from collisional quenching of electronicallyexcited OH A ~2Σ+byN_2has been determined using a pump-probe technique. The majority of OHX 211 products are observed in their lowest vibrational level, υ"=0, with significantly less populationin υ"= 1. The OH (υ"=0) products are generated with a substantial degree of rotational excitation,peaking around N"=18, with an average rotational energy of —6500 cm~-1.A preference is found forthe OH IRA') Λ-doublet, indicating some degree of Pπ- orbital alignment. The branching fractioninto OH X ~2Пproduct states demonstrates that nonreactive quenching is the dominant decaypathway for quenching of OH A ~2Σ+byN_2.The topography of the conical intersection region thatcouples the electronically excited and ground state potential energy surfaces is also examinedtheoretically. The rotational excitation of the OH X ~2Пproducts and branching fraction are found tobe dynamical signatures of nonadiabatic passage through the conical intersection region.