Solvation effects on the A-band photodissociation of dibromomethane: Turning a photodissociation into a photoisomerization

We have obtained A-band resonance Raman spectra of dibromomethane in the ga s and solution phase and nanosecond time-resolved resonance Raman spectra o f dibromomethane photoproducts. The A-band resonance Raman spectra suggest the short-time dynamics are similar to other dihalomethanes that an known t o have direct photodissociation reactions in the gas phase. Several power d ependent A-band resonance Raman bands were tentatively assigned to the C-Br stretch overtone progression of the CH2Br radical which has a strong absor ption band that is coincident with the A-band resonance Raman excitation wa velength. Two-color nanosecond time-resolved resonance Raman spectra (266.0 nm pump/341.5 nm probe) were obtained and comparison of the vibrational fr equencies to the results for density functional theory calculations indicat e that the iso-CH2Br-Br species is mainly responsible for the transient pho toproduct absorption band similar to 360 nm. Our preliminary results for A- band photoexcitation of dibromomethane in conjunction with previously repor ted diiodomethane results suggest that solvation effects (probably via reco mbination of the CH2Br and Br fragments within a solvent cage) lead to noti ceable production of the isodibromomethane photoisomerization photoproduct observed in the nanosecond time-resolved resonance Raman spectra.