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

We report the collision energy dependence of the cross sections for excitation of N 2 (C 3Π u) to individual vibrational levels in collisions of N 2(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 N 2(C) excited in collisions with Kr* ( 3P 0 ) and Kr* ( 3P 2) 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 + +N 2- (X 2Π g). For Ar* the model predicts a threshold Δ E= 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 Δ E≤8 me V observed by Parr and Martin and by Winicur and Fraites. The difference is tentatively assigned to the 3P 0: 3P 2 beam composition or the initial rotational temperature of the N 2. Also, excitation of N 2(C) by Xe*( 3P 0) at collision energies E > 1.5 e V is observed. The resulting cross section indicates that the excitation probability for N 2(C) by Xe* ( 3P 0) is comparable to that for Ar* and Kr*.