On the use of photoelectron spectroscopy to probe the dynamics of a dissociative intermediate state

An in-depth experimental investigation into the use of photoelectron spectroscopy to probe the dynamics of a dissociative intermediate state is reported here. More than 70 velocity-mapped photoelectron images were acquired from either one-colour or two-colour two-photon ionization processes, covering the energy range from the ionization limit of CH3I to about 3600 cm 1 above the IP. Numerous autoionizing states, both vibrationless and vibrationally excited, were observed and spectroscopically assigned. The finial ion state distributions, derived from the photoelectron kinetic energy analysis, are highly selective both in vibrational modes and in quantum numbers, as well as exhibit sensitive dependences on photon energy. These findings were interpreted as a manifestation of vibronic autoionization processes rather than a direct reflection of the dissociation dynamics of the resonant intermediate state in the (1þ 1) resonance-enhanced multiphoton ionization of CH3I as suggested in previous studies.