Excitation transfer collisions of metastable Ar*, Kr* and Xe* atoms with N2 (X, ν = 0 ): collision energy dependence of excitation cross sections and product vibrational distribution of N2(C 3Πu, ν′ = 0, 1, 2, 3)

Abstract

We report the collision energy dependence of the cross sections for excitation of N2 (C 3Πu) to individual vibrational levels in collisions of N2(X, ν=O) with Ar* and Kr* obtained in crossed beam experiments. The range of collision energies covered is 0.08 < E (eV) < 3 for Ar* and 0.4<E (eV) < 3 for Kr*. With Ar* the vibrational distribution is almost independent of collision energy and decreases with increasing vibrational quantum number. The vibrational distribution of N2(C) excited in collisions with Kr* (3P0 ) and Kr* (3P2) shows similar behaviour. The results are compared to simple models for excitation transfer through a single curve crossing between the initial and final states and through two curve crossings including an intermediate ionic state with distorted Franck-Condon factors to account for vibrational excitation. The cross sections obtained for Ar* are in general agreement with an intermediate state model but cannot be explained by a single curve crossing model. For Kr* the results are compatible with both. The intermediate state is identified as Ar+, Kr+ +N2− (X 2Πg). For Ar* the model predicts a threshold ΔE= 63 meV of the initial state curve crossing for the excitation process, independent of the final vibrational level. This value is outside the energy range covered in this work, and larger than the threshold ΔE≤8 me V observed by Parr and Martin and by Winicur and Fraites. The difference is tentatively assigned to the 3P0: 3P2 beam composition or the initial rotational temperature of the N2. Also, excitation of N2(C) by Xe*(3P0) at collision energies E > 1.5 e V is observed. The resulting cross section indicates that the excitation probability for N2(C) by Xe* (3P0) is comparable to that for Ar* and Kr*.