H+N 2 O collision dynamics: Branching ratios for T–V energy transfer and the effect of N2O vibrational excitation on the reaction kinetics

We report time-resolved Fourier transform spectroscopic measurements on the kinetics of the reaction of vibrationally excited N2O with hydrogen atoms. Vibrationally excited N2O is formed by T–V energy transfer in collisions with hydrogen atoms having 2.3 eV of translational energy. Although the T–V process is capable of exciting the N2O to vibrational levels up to 18 500 cm−1, collisions in which the relative translational energy is greater than 11 000 cm−1 result in rapid reaction to form either NH(X 3Σ)+NO(X 2Π) or OH(A 2Σ+)+N2(X 1Σ+). N2O which is vibrationally excited to energies between 6000 and 11 000 cm−1, reacts with thermal hydrogen atoms, with a rate constant which is about 1.7×10−10 cm−3 molecule−1 s−1. N2O vibrationally excited to levels below 6000 cm−1 [the height of the barrier to reaction forming OH(X 2Π)+N2 on the ground-state surface] is lost very slowly, presumably by deactivation, with a rate constant which is about four orders of magnitude slower than the reaction. The results indicate that increasing the vibrational energy of the N2O by 11 000 cm−1 increases the cross section for the reaction with hydrogen atoms by about seven orders of magnitude.