The S1(n,*) S0 cavity ringdown spectrum of 2-cyclohexen-1-one vapor has been recorded in the vicinity of the 000 band, which is at 26 089.1 cm1. Observation of hot bands in the spectrum has permitted the determination of several low-frequency fundamentals and overtones in the ground electronic state. The lowest two excited quantum states for the inversion vibration (v39) were found to be at 99.0 and 197.0 cm1. Together with previously published far-IR spectra and vapor-phase Raman spectra, the fundamental frequencies for v39, v38, and v37 have been determined. From observed v39 levels, the barrier to inversion has been determined experimentally to be 1900 300 cm1, which is very different from values of 935 and 3379 cm1 previously reported from Raman and far-IR data, respectively. Density functional calculations carried out in this paper give a barrier value of 2090 cm-1 when the B3LYP/6-311+G(d,p) basis set is used.Key words: cavity ringdown spectra, 2-cyclohexen-1-one, Raman spectra, potential energy function, inversion barrier.