We report a combined experimental and theoretical study of the low-lying electronic states of cyclopentadienone (C5H4O). The cyclopentadienone anion (C5H4O-) was generated in the gas phase via reaction of atomic oxygen radical anions (O-) with cyclopentanone (C5H8O). Photoelectron imaging was used to gain access to the first three electronic states of C5H 4O, including the X 1A1 ground state and the 3B2 and 3A2 excited states. The first two state assignments are supported by the Franck-Condon simulations of the vibrational progressions observed in the X 1A1 and 3B2 bands in the photoelectron spectra. The adiabatic electron affinity of cyclopentadienone in the ground state is determined to be EA(X 1A1) = 1.06 ± 0.01 eV, and the corresponding values for the first two excited states are EA(3B2) = 2.56 ± 0.02 eV and EA(3A2) = 3.45 ± 0.01 eV. These experimental determinations are in excellent agreement with the CCSD(T) theory predictions, lending further confidence to the above state assignments. On the basis of these results, the lowest singlet-triplet splitting (between the X 1A1 and 3B2 states) in cyclopentadienone is ΔES-T = 1.50 ± 0.02 eV.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry