Vibronic structure of the 3s and 3p Rydberg states of the allyl radical.

Resonance-enhanced multiphoton ionization combined with electronic ground state depletion spectroscopy of jet-cooled allyl radicals (C3H5) provides vibronic spectra of the 3s and 3p Rydberg states. Analysis of the vibronic structure following two-photon excitation of rovibrationally cold allyl radicals reveals transitions to the 3p(z) ((2)A(1)) Rydberg suite with an electronic origin at 42230 cm(-1). More than 40 transitions to vibrational levels in the partially overlapping spectra of the 3p(y) (B-2(2)) Rydberg state and the 3s ((2)A(1)) Rydberg state are identified and reassigned on the basis of predictions from ab initio calculations and results and simulations of pulsed-field-ionization zero-kinetic-energy photoelectron spectra obtained recently using resonant multiphoton excitation via selected vibrational levels of these two Rydberg states (J. Chem. Phys. 2009, 131, 014304). Depletion spectroscopy reveals that the transition to the short-lived 3p(x) (B-2(1)) Rydberg state in vicinity of three-state same symmetry conical intersections predicted theoretically carries most of the oscillator strength of these coupled 3s and 3p Rydberg states. The results allow for the first time to experimentally derive the energetic ordering of the 3p Rydberg states of the allyl radical.