H- BRANCHING RATIOS FOR T-V ENERGY-TRANSFER AND THE EFFECT OF N2O VIBRATIONAL-EXCITATION ON THE REACTION-KINETICS(N2O COLLISION DYNAMICS )

We report time-resolved Fourier transform spectroscopic measurements o n the kinetics of the reaction of vibrationally excited N2O with hydro gen atoms. Vibrationally excited N2O is formed by T-V energy transfer in collisions with hydrogen atoms having 2.3 eV of translational energ y. Although the T-V process is capable of exciting the N2O to vibratio nal levels up to 18500 cm(-1), collisions in which the relative transl ational energy is greater than 11000 cm(-1) result in rapid reaction t o form either NH(X (3) Sigma) + NO(X (II)-I-2) or OH(A (2) Sigma(+)) N-2(X (1) Sigma(+)). N2O which is vibrationally excited to energies b etween 6000 and 11000 cm(-1), reacts with thermal hydrogen atoms, with a rate constant which is about 1.7 X 10(-10) cm(-3) molecule(-1) s(-1 ). N2O vibrationally excited to levels below 6000 cm(-1) [the height o f the barrier to reaction forming OH(X (II)-I-2) + N-2 on the ground-s tate 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 11000 cm(-1) increases the cross section for the reactio n with hydrogen atoms by about seven orders of magnitude. (C) 1997 Ame rican Institute of Physics.