Density Functional Calculations, Structure, and Vibrational Frequencies of 2-Cyclopenten-1-one in Its S0, S1(n,π*), T1(n,π*), and T2(π,π*) States

Abstract

Density functional calculations have been carried out on the S0, S1(n,π*), and T1(n,π*) states of 2-cyclopenten-1-one (2CP) to complement the experimental study of the triplet state using cavity ringdown spectroscopy described in the previous paper. Structures and vibrational frequencies were calculated for each state at both the B3LYP/6-31+G(d,p) and B3LYP/6-311+G(d,p) levels. The structural information was used to obtain the kinetic energy part of the ring-bending Hamiltonian, for the analysis of triplet-state spectral data. The density functional calculations show the molecule in its S0 and S1 states to be planar, but to have a small barrier to planarity in the T1(n,π*) triplet state. This is in line with potential-energy fits to the experimental ring-bending levels for each state. The calculated barrier for the T2(π,π*) state is 999 cm-1. This provides further confirmation that the cavity ringdown data, from which a 43-cm-1 barrier was determined, correspond to the T1(n,π*) state. The calculated vibra...