Reaction dynamics of Y + O2 → YO(X,A′,A) + O(3PJ) studied by the crossed-beam technique

Abstract

The dynamics of the reaction, Y + O₂ → YO + O was studied by using the crossed-beam technique at several collision energies from 10.3 to 52.0 kJ mol⁻¹. The Y atomic beam was generated by laser vaporization and crossed with the O₂ beam at a right angle. Among the energetically accessible electronic states of YO, the formation of the A²Π and A′²Δ states was observed by their chemiluminescence at all collision energies. By analyzing the chemiluminescence spectra of YO(A²Π_1/2,3/2–X²Σ⁺), vibrational state distributions and relative populations of spin–orbit states were determined for YO(A²Π_1/2,3/2). At low collision energies, the vibrational distributions agree quite well with those expected from the statistical energy partitioning, while a little deviation from the statistical expectation was observed at the highest energy, 52.0 kJ mol⁻¹. The populations of two spin–orbit states are in good agreement with the statistical expectations at all collision energies. The vacuum ultraviolet laser-induced fluorescence (VUV-LIF) technique was employed to determine the distributions of spin–orbit states of the product O(³P_J) at two collision energies, 20.7 and 52.0 kJ mol⁻¹. The line shapes of the O atom transitions were analyzed to determine relative branching ratio of the ground state to the excited states of YO, i.e. YO(X²Σ⁺) + O(³P_J) vs. YO(A²Π and A′²Δ) + O(³P_J). The results showed that the electronically excited YO was formed with comparable amount with the ground state which is statistically more favorable, and suggested the occurrence of two mechanisms taking place in the title reaction.