On the Quenching of O(1D) by N2 and Related Reactions

Abstract

As an extension of earlier work on the quenching of electronically excited alkali metal atoms by N2 and CO, that uses a model of curve crossing involving an ionic intermediate state, here we treat the quenching of O(1D) by N2, a process which proceeds by curve crossing of covalent states. The model is also applied to the vibrational relaxation of N2 in collision with O(3P) atoms and to the unimolecular decomposition of N2O. The order of magnitude of the rate constants for all three processes can be explained by the present model, using the same value of the electronic coupling potential for the curve-crossing process; this value is significantly larger than the corresponding value for isolated O(3P) and O(1D) atoms. In the quenching of O(1D) by N2, the electronic-vibrational coupling is weak, channeling less than 5% of the electronic quantum into vibrational levels of N2, but the quenchant N2 is likely to be rotationally excited. The vibrational relaxation of N2 by oxygen atoms arising due to curve crossing rather than to adiabatic (Landau-Teller) collisions has a significant activation energy, ∼0.8 eV, so that the rate coefficient for vibrational relaxation due to curve crossing is expected to show a strong temperature dependence and to dominate at temperatures above 600°K.