Photodissociation of molecular beams of methylene iodide and iodoform

Abstract

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.