Jet-cooled fluorescence excitation spectrum, carbonyl wagging, and ring-puckering potential energy functions of 3-cyclopenten-1-one in its S1(n,π*) electronic excited state

Abstract

The jet-cooled fluorescence excitation spectrum of 3-cyclopenten-1-one has been recorded in the 308–330 nm region, and the electronic origin for the S1(n,π*) state of A2 symmetry was observed at 30 229 cm−1. The observed spectrum consists of more than 80 bands involving primarily ν3 (carbonyl stretch), ν29 (carbonyl out-of-plane wagging), and ν30 (ring puckering). Bands were also assigned to combinations with seven other vibrational modes. The energies for the v=0 to 11 quantum states of ν29 were measured and used to determine a one-dimensional potential energy function. This function has energy minima at wagging angles of ±24° and a barrier to inversion of 939 cm−1. Four bands associated with ν30 were observed and were used to determine an asymmetric single-minimum one-dimensional ring-puckering potential energy function for the S1(n,π*) state. The ring-puckering energy levels in the ν29 vibrational excited states are little changed from the v=0 state indicating that there is little interaction between the carbonyl wagging and the ring-puckering motions.