Femtosecond photolysis of CH2Br2 in acetonitrile: Capturing the bromomethyl radical and bromine-atom charge transfer complex through deep-to-near UV probing

Dibromomethane (CH2Br2) in acetonitrile is a suitable precursor to characterize the absorption signatures of the CH2Br radical and solvent Br charge-transfer complexes. Following irradiation of CH2Br2 at 255 nm, the iso-H2CBrBr isomer product rapidly converts back to the parent species, and transient absorption spectra reveal the bands of solvent-separated radical species, the CH2Br radical peaking at 235 nm, as well as the CH3CN·Br complex at 272 nm. The absorption of CH2Br exhibits minor solvatochromic shifts upon going from acetonitrile to cyclohexane, and the molecular decadic extinction coefficient of CH3CN·Br is estimated to be 1470 M−1 cm−1.