Photochemistry of Iodoform in Methanol: Formation and Fate of the Iso-CHI2-I Photoproduct

Ultrafast population and structural dynamics due to the iso-CHI2-I isomer product formed upon UV excitation of iodoform (CHI3) in solution is monitored by femtosecond transient absorption with deep-UV through near-IR probing and picosecond transient resonance Raman spectroscopy. Iso-CHI2-I is found to be a major photochemical product regardless of excitation wavelength (266 and 350 nm) and choice of solvent (methanol, acetonitrile, and cyclohexane), and is produced in 50% quantum yield upon 266 nm excitation of CHI3 in CH3OH. The isomer remains stable up to at least several nanoseconds in C6H12 and CH3CN, but undergoes decay with a 740 ps lifetime in CH,OH simultaneously with the formation of an iodide ion. In agreement with the experiments, MP2 calculations suggest that iso-CHI2-I readily reacts with CH3OH via O-H insertion/HI elimination reactions.