Concerted elimination dynamics from highly excited states

Abstract

Photoinduced molecular detachment has been investigated for methylene iodide (CH₂I₂) and several related compounds (CH₂Br₂, CH₂Cl₂ and CF₂Br₂). Multiphoton excitation of these molecules at 310 nm gives rise to halogens in the D′ state. Femtosecond pump-probe experiments on the dissociation of these compounds indicate that the process is extremely fast (<60 fs) and proceeds without an intermediate. In addition to the characteristic D′→A′ fluorescence at 342 nm, photodissociation of CH₂I₂ also produces several fluorescence bands in the 260–290 nm region. The CH₂I₂ transients show characteristic I₂ vibrational coherence. Time resolved data collected by detection at 272 nm also demonstrate clear, fast decaying rotational anisotropy, analysis of which reveals a distribution of rather high rotational levels of I₂. Based on analysis of the dissociation time, rotational anisotropy and vibrational coherence, and on the estimated partitioning of energy in the fragments, an I₂ concerted molecular detachment mechanism has been proposed.