Ultrafast Study of the Photodissociation of Bromoiodomethane in Acetonitrile upon 266 nm Excitation

We studied the A-band photodissociation of bromoiodomethane, CH 2 BrI, in acetonitrile solution at room temperature by femtosecond pump−probe spectroscopy. Initiated by the 266 nm light, this reaction leads to the CH 2 Br−I isomer, most likely produced via in-cage recombination of the CH 2 Br and I photofragments. The isomer is formed vibrationally excited with a time constant of ∼7.5 ps and the hottest isomer molecules are observed as early as 1 ps after the UV excitation. Vibrational relaxation of the isomer molecules takes place on two distinct time scales of a few and ∼40 ps. The ground-state lifetime of the isomer is about 2.5 ns.