Photodissociation study of CH 3 Br in the first continuum

The photolysis of CH3Br is studied in the energy region of the A band between 4.94 and 5.76 eV using ion imaging. Velocity distributions for both the bromine-atom and methyl-radical photofragments are determined. Our results indicate that transitions to the Q0 and Q1 states dominate the absorption cross section and the partial cross section to each state is determined. The @Br* #/@Br# branching ratio is found to be strongly dependent on the excitation energy varying between 0.6 and 1.5. Both the bromine-atom and the methyl-radical translational energy distributions suggest that the vibrational distribution in the nascent CH 3 is nonstatistical with appreciable excitation in thev2 umbrella mode. The lifetime of theA band is estimated at t 5120640 fs. © 1998 American Institute of Physics. @S0021-9606 ~98!00114-7#