Activation threshold for vibrational excitation in K-N 2 collisions

Abstract

In K-N 2 collisions the onset of molecular vibration is found to occur at a collision energy E c = 1.36 ± 0.1 eV. With N 2 in its ground vibrational level initially the O→4 transition of endoergicity Δ E(0–4) = 1.134 eV is observed. Below E c none of the lower transitions is excited. Above E c they probably also occur, but cannot be detected in the translation energy loss experiment because of strong concurrent rotational excitation in the 0→0 channel. The 0→4 transition tends to saturate at about 1.62 eV, the first electronic excitation energy of the K atom, where it contributes 6–7° of total scattering into angle ϑ = 140°. The activation of vibration is caused by non-adiabatic transitions. Its onset is a direct probe to the avoided crossing of the X̄ 2A′ and Ā 2A′ potentials of K-N 2 which also promote collisi excitation and quenching of K resonance radiation. Some bearing of the present results on the latter phenomena and their understanding is discussed.