Vibrational populations of N₂(B³Πg) and CO(a³Π) produced by He⁺impact on N₂(X) and CO(X) in the 200-1000 eV energy range

High-resolution energy loss spectra (ELS) for the production of N 2 (B 3 Pi g ) and CO(a 3 Pi ) in collisions of He + on N 2 (X 1 Sigma g + ) and CO(X 1 Sigma + ) have been obtained in the 200 eV<or=E<or=1 keV energy range. The present study of vibronic excitation at low energies has been made possible by the use of a microchannel-plate detection device. The measured vibrational distributions show a non-Franck-Condon (FC) behavior for E<500 eV in the case of N 2 . In the case of CO, deviations from FC distributions are found in the entire energy range. To explain the differences between the ELS of N 2 and CO at E>500 eV, the authors invoke in the case of CO long-range charge dipole interactions that perturb the entrance channel prior to (and/or the exit channel after) the electronic transition. For E<500 eV the deviations from FC distributions in both the N 2 and CO cases are tentatively attributed to perturbations caused by near-resonant charge exchange channels.