CONCERTED ELIMINATION DYNAMICS FROM HIGHLY EXCITED-STATES

Photoinduced molecular detachment has been investigated for methylene iodide (CH2I2) and several related compounds (CH2Br2, CH2Cl2 and CF2Br 2). Multiphoton excitation of these molecules at 310 nm gives rise to halogens in the D' state. Femtosecond pump-probe experiments on the di ssociation of these compounds indicate that the process is extremely f ast (<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 regio n. The CH2I2 transients show characteristic I-2 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 I-2. Based on analy sis of the dissociation time, rotational anisotropy and vibrational co herence, and on the estimated partitioning of energy in the fragments, an I-2 concerted molecular detachment mechanism has been proposed.