The fluorescence excitation spectra of bicyclo[3.1.0]hexan-3-one have been recorded and assigned, almost exclusively to combinations of the ring-puckering and out-of plane carbonyl-wagging vibrations. One-dimensional potential energy functions were calculated for both of these modes in the S-1(n,pi*) excited state. The carbonyl-wagging vibration has a barrier to inversion of 860 +/- 30 cm(-1), and its potential function appears to have very little asymmetry. The ring-puckering function has a single minimum and is considerably stiffer in the S-1 state than in the ground state.