METHYL-IODIDE A-BAND DECOMPOSITION STUDY BY PHOTOFRAGMENT VELOCITY IMAGING

The methyl iodide A-band photodissociation process CH3I+h nu-->CH3(ups ilon,N,K)+I(P-2(3/2)), I(P-2(1/2)) has been studied in a cold molecul ar beam. Full three-dimensional state-specific speed and angular distr ibutions of the nascent fragments were recorded using (2+1) resonance- enhanced multi-photon ionization (REMPI) and velocity imaging, a new v ariant of ion imaging. By combining the I quantum yield and anisotrop y parameters for both I and I channels, the relative absorption stren gth to the contributing electronic states ((3)Q(0), (3)Q(1) and (1)Q(1 )) as well as the probability for curve crossing ((3)Q(0)-->(1)Q(1)) a re determined for excitation wavelengths across the full A band (240-3 34 nm). Parallel excitation to the (3)Q(0), state turns out to dominat e the A band even more than previously thought. (C) 1998 American Inst itute of Physics.