Single-photon and resonance-enhanced multiphoton threshold ionization of the allyl radical.

Pulsed-field-ionization zero-kinetic-energy photoelectron spectra of jet-cooled allyl radical (C(3)H(5)) have been recorded following single-photon and resonant multiphoton excitation. Simulations based on an orbital ionization model and rovibronic photoionization selection rules reliably describe the observed intensity distributions in the photoelectron spectra obtained from single-photon excitation from the ground state and resonant multiphoton excitation via the 3s and the 3p Rydberg states. More than 30 transitions to vibrational levels of the cation were identified and assigned on the basis of predictions from ab initio calculations.