Theoretical studies of fast H atom collisions with NO

This paper presents a detailed theoretical study of the NO vibration/rotation distributions produced in nonreactive H + NO collisions in the 1-3 eV range of relative translational energies. The collision dynamics is studied by applying the quasiclassical trajectory method to each of the four potential surfaces (¹A′, ¹A″, ³A′, ³A″) which correlate to H(²S) + NO(²Π), followed by a statistical average of the cross sections over the four surfaces. Each surface is generated by fitting a flexible empirical function (a sum of Morse functions with coordinate dependent parameters) to available ab initio and experimental data on the surfaces. The resulting vibrational distributions are in excellent agreement with measured laser induced fluorescence results at 0.95 and 2.2 eV. In addition, the average fraction of energy transferred into vibration shows the same flat dependence on translational energy in the 1-3 eV range that is seen experimentally, and which contrasts with the linear proportionality seen for the corresponding H + CO system. Details of the collisions are analyzed, and it is found that complex formation plays a much more important role in H + NO than in H + CO, with roughly 2/3 of the cross section at 0.95 eV and 1/5 that at 2.2 eV due to complex formation. In fact, at both energies, the trajectory vibrational distributions are quite close to statistical. At 2.2 eV, however, direct collisions make a substantial contribution to the vibrational excitation process, so the agreement with statistical theory is partly accidental. The rotational distributions are found to be substantially colder than statistical, particularly at higher energy, with an average rotational quantum number which is independent of vibrational state except for the highest three states allowed by energy conservation. Agreement between experimental and theoretical rotational distributions is poorer than for the vibrational distributions, with the theoretical rotational distributions being hotter. This presumably reflects errors in the anisotropy of the potential energy surfaces.