Rydberg states of the allyl radical observed by two-photon resonant ionization spectroscopy

The vibronic spectrum of the allyl radical (CH2CHCH2) at 6-8 eV has been observed using 2+1 resonance-enhanced multiphoton ionization (REMPI) spectroscopy. The allyl radicals were produced in the nozzle of a supersonic jet expansion by the pyrolysis of allyl iodide. Five new Rydberg states, a 3d and four ns states (n=4,6-8), are observed for the first time. Prominent vibrational progressions with the gross spacing of similar to 430 cm(-1) are observed in the s Rydberg series. The totally symmetric angle CCC-bending vibration in the Rydberg states is responsible for the observed vibrational progressions. Facilitated with the ab initio calculation of Franck-Condon factors, other observed vibrational states in the s Rydberg series have been identified. The term values for the ns Rydberg series converge to an adiabatic ionization energy of 65 638 +/- 18 cm(-1) with a quantum defect of 0.966 +/-0.005. (C) 2000 American Institute of Physics. [S0021-9606(00)31141-2].