RYDBERG STATES OF ALLYL RADICAL OBSERVED BY ONE-AND TWO-PHOTON RESONANT IONIZATION SPECTROSCOPY

$^{a}$ D. W. Minsek and P. Chen, J. Phys. Chem., 97, 13375 (1993). $^{b}$ T.-K. Ha, H. Baumann and J. F. M. Oth. J. Chem. Phys., 85, 1438 (1986). $^{c}$ A. D. Sappey and J. C. Weisshaar, J. Phys. Chem., 91, 3731 (1987).Author Institution: Department of Chemistry, Institute of Atomic and Molecular Sciences National Taiwan University, Institute of Atomic and Molecular Sciences, Academia SinicaThe vibronic spectrum of allyl radical $(CH_{2}CHCH_{2})$ at 4.9-8.2 eV has been observed using $1+1$ and $2+1$ 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. The vibronic assignment for the congested $\tilde{B}1_{2}A_{1}(\pi \rightarrow 3s), \tilde{C} 2^{2}B_{1}(\pi \rightarrow 3px)$ and $\tilde{D}1_{2} B_{2} (\pi \rightarrow n^{*})$ bands at 4.9-5.2 eV will be reexamined with aid of the calculated Franck-Condon factors, especially for the weaker transitions at $> 5.2$ eV which were not identified in previous $study^{a}$. Three new electronic bands are observed for the first time and assigned to the $3^{2}B_{1} (\pi \rightarrow 3d_{xz}), 2^{2} A_{2}(\pi \rightarrow 3d_{xy})$ and $3^{2} A_{1}(\pi \rightarrow 3p_{z})$ Rydberg states based on the ab initio Cl $calculation.^{b}$ The observed band origins (in eV) at 6.460 $(3^{2}B_{1}), 6.607 (2^{2} A_{2})$ and $7.605 (3^{2} A_{1})$ are compared with the calculated vertical energies of 6.41, 6.62 and 7.55, respectively. Vibrational progressions with the gross spacings of $\sim 420 cm^{-1}$ are observed in the Rydberg states. The totally symmetric $\angle CCC$ bending in the excited state is responsible for the observed progression as that reported in the $\widetilde{B}$ $state.^{c}