Faraday Discuss., 1997, 108, 63È80 Concerted elimination dynamics from highly excited states

Photoinduced molecular detachment has been investigated for methylene iodide and several related compounds and(CH2I2) (CH2Br2, CH2Cl2Multiphoton excitation of these molecules at 310 nm gives rise toCF2Br2).halogens in the D @ state. Femtosecond pump-probe experiments on the dis-sociation of these compounds indicate that the process is extremely fast (\60 fs) and proceeds without an intermediate. In addition to the character-istic D@] A @ Ñuorescence at 342 nm, photodissociation of also pro-CH2I2duces several Ñuorescence bands in the 260È290 nm region. The CH2I2transients show characteristic vibrational coherence. Time resolved dataI2collected by detection at 272 nm also demonstrate clear, fast decaying rota-tional anisotropy, analysis of which reveals a distribution of rather high rotational levels of Based on analysis of the dissociation time, rotationalI2.anisotropy and vibrational coherence, and on the estimated partitioning of energy in the fragments, an concerted molecular detachment mechanismI2has been proposed.