Molecular dynamics of metastable atomic reactions: translational energy threshold and product rotational alignment in the reaction of Xe(³P_2,0) with CH₃Br

Abstract

Relative cross-sections for the reaction of Xe(³ P _2,0) with CH₃Br have been measured under crossed-beam conditions over the centre of mass collision energy range 6⩽tE _t⩽70 kJ mol^-1. The excitation function, which qualitatively resembles that for the analogous alkali metal atomic reaction, has a clear threshold at E _t = 7 ± 3 kJ mol^-1. A small increase in the vibrational energy of the CH₃Br leads to a pronounced shift in the maximum of the translational excitation function toward lower energies. The rotational alignment in the XeBr increases slowly with E _t. The results are consistent with (i) impulsive rebound dynamics, (ii) a late energy barrier in the exit channel, (iii) induced repulsive energy release with increasing collision energy.