Methyl iodide A-band decomposition study by photofragment velocity imaging

Abstract

The methyl iodide A-band photodissociation process CH3I+hν→CH3(v,N,K)+I(2P3/2), I*(2P1/2) has been studied in a cold molecular beam. Full three-dimensional state-specific speed and angular distributions of the nascent fragments were recorded using (2+1) resonance-enhanced multi-photon ionization (REMPI) and velocity imaging, a new variant of ion imaging. By combining the I* quantum yield and anisotropy parameters for both I and I* channels, the relative absorption strength to the contributing electronic states (3Q0, Q13 and Q11) as well as the probability for curve crossing (3Q0→1Q1) are determined for excitation wavelengths across the full A band (240–334 nm). Parallel excitation to the Q03 state turns out to dominate the A band even more than previously thought.