Photodissociation of molecular beams of methylene iodide and iodoform

Molecular beams of CH2I2 and CHI3 have been dissociated by polarized ultraviolet light and the angular distribution of the fragments has been measured. The photofragment mass spectra show that the lower lying excited states of CH2I2 and CHI3 dissociate to give an iodine atom and the corresponding radical. The angular distribution fitted the form 1+βP2(ϑ), where ϑ is the angle between the detection and polarization directions. β was 0.90±0.16 for CH2I2 and 0.46±0.16 for CHI3. These values prove that the molecule dissociates in a time short compared to its period of rotation. Moreover, the first two absorption bands in CH2I2 are shown to be of A1→B1 type polarized along the I–I vector, and in CHI3 they are of A1→E type polarized perpendicular to the threefold axis. A crude exciton model amounts for the number and symmetries of the energy states.