Molecular dynamics of metastable atomic reactions: translational energy threshold and product rotational alignment in the reaction of Xe(3P2,0) with CH3Br

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.