Rovibronic energy transfer from N2(a 1πg) to CO(A 1π) studied by laser REMPI spectroscopy

Abstract

The collision-induced electronic energy transfer N2(a 1πg,v′) +CO(X 1Σ+,v″=0) →N2(X 1Σ+g,v″) +CO(A 1πg,v′)+ΔE is studied in a gas cell. N2(a 1πg,v′, J′) is prepared by two-photon (2hν1) absorption from the ground state. CO(A 1πg,v′, J′) is probed by two-photon (hν1+hν2) ionization via CO(B 1Σ+) as the resonant intermediate state. Experiments show that the overall energy transfer cross sections exceed that of gas kinetic collisions by a factor of 3–4. The energy mismatch ΔE is the determining factor controlling the branching ratio from one N2(1πg,v′) donor to different vibrational levels of CO(A 1π,v′). For small values of ΔE, CO(A 1πg,v′, J′) shows a Boltzmann-like rotational level population. Its rotational temperature scales with ΔE. About 28% of the excess energy funnels into the rotation of CO(A 1π). An explanation for the observed rotational distribution of CO* and the energy transfer mechanism is given. The rate constants are analyzed in terms of the surprisal.