Knowledge Bank

The vibronic spectrum of allyl radical $(CH2CHCH2)$ 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 $B~12A1(\pi \to 3s),C~22B1(\pi \to 3px)$ and $D~12B2(\pi \to n\ast )$ 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 $studya$. Three new electronic bands are observed for the first time and assigned to the $32B1(\pi \to 3dxz),22A2(\pi \to 3dxy)$ and $32A1(\pi \to 3pz)$ Rydberg states based on the ab initio Cl $calculation.b$ The observed band origins (in eV) at 6.460 $(32B1),6.607(22A2)$ and $7.605(32A1)$ are compared with the calculated vertical energies of 6.41, 6.62 and 7.55, respectively. Vibrational progressions with the gross spacings of $\sim 420cm-1$ 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 $B~$ $state.c$