Reactive quenching of OH A (2)Sigma(+) in collisions with molecular deuterium via nonadiabatic passage through a conical intersection

The D and H atom products from collisional quenching of OH A (2)Sigma (+) ( v = 0) by D-2 have been examined through Doppler spectroscopy using two-pho ton (2 S-2 <-- <-- 1 S-2) laser-induced fluorescence. A bimodal Doppler pro file is observed for the D atoms, indicating that two different velocity di stributions result from the OH A (2)Sigma (+) + D-2 --> D + HOD reaction. N early 40% of the products are H atoms produced in the OH A (2)Sigma (+) + D -2 --> H + D2O reaction with a single Gaussian profile. The two components of the D atom kinetic energy distribution are characterized by translationa l temperatures of approximately 1200 and 10 000 K and on average account fo r 4% and 30% of the available energy. The H atom products accommodate about 37% of the available energy and are described by a 13 000 K temperature. T he translational energy distributions of the H/D atom products are attribut ed to two dynamical pathways through the strong nonadiabatic coupling regio n at the HO-D-2 conical intersection. The narrow "cold" distribution of D a toms arises from an abstraction reaction in a direct passage through the co nical intersection region. The broad statistical distribution observed for both D and H atom products suggests that the HO-D2 collision pair lives lon g enough on the excited-state surface for energy to randomize before evolvi ng through the conical intersection that leads to products.