CH3Br is photodissociated in the first continuum. Dissociation takes place into ground state CH3and Br [ = Br(2P3 2] or Br* [ = Br(*P1 2)]. Time of flight and angular distributions of the CH3fragments are measured. The Br*/Br ratios upon excitation at 222 and 193 nm are found to be 1.00 and 0.20 respectively. The anisotropy parameters at these wavelengths are β = 0.28±0.04 and β = -0.23±0.02, respectively. The total absorption cross section is decomposed into partial absorption cross sections of the1Q,3Q0and3Q1states. It appears that excitation at 222 nm takes place to the3Q0and3Q1states whereas at 193 nm the1Q and3Q0states are excited. Contrary to CH3I, the adiabatic curve crossing between the3Q0and the1Q states in Ch3Br is not important. The dissociation energy of the CBr bond is determined to be D0(CH3Br) = 2.87±0.02 eV. © 1985.
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