15min:

H. J. WÖRNER AND F. MERKT, PHYSIKALISCHE CHEMIE, ETH ZÜRICH, CH-8093 ZÜRICH.

This presentation summarizes the results of the first photoelectron spectroscopic study of the cyclopentadienyl radical. The cyclopentadienyl radical was produced in a supersonic expansion by photolysis of cyclopentadiene at 248 nm using the method described in Ref. a. PFI-ZEKE photoelectron spectra were recorded using two different excitation schemes. In the first experiment single-photon excitation from the X ²E₁'' ground state of the radical was used to study the ground state of the cyclopentadienyl cation. In the second experiment, a resonance-enhanced two-photon excitation scheme via the vibrationless transition to the A ²A₂'' studied in Ref. b provided access to the first electronically excited state of the cyclopentadienyl cation. The analysis of the spectra reveals that the ground state of the cyclopentadienyl cation is a triplet state of electronic symmetry ³A₂' and the first excited state is a singlet of symmetry ¹E₂', which is subject to a pronounced Jahn-Teller distortion. The results of ab initio calculations together with a preliminary analysis of the Jahn-Teller effect in the ¹E₂' state are presented.
, 1152 (2003).
b. L. Yu, S.C. Foster, J.M. Williamson, M.C. Heaven and T.A. Miller, J. Chem. Phys. 92, 4263 (1988).