The cavity ringdown spectra of 2-cyclohexen-1-one (2CHO) and its 2,6,6-d(3) isotopomer (2CHO-d(3)) have been recorded in the spectral region near their S-1(n,pi*)<- S-0 band origins which are at 26 081.3 and 26 075.3 cm(-1), respectively. The data allow several of the quantum states of nu(39), the ring inversion, to be determined for both the ground and excited electronic states. These were utilized to calculate the one-dimensional potential energy functions which best fit the data. The barriers to inversion for the S-0 and.S-1(n,pi*) states were found to be 1900 +/- 300 and 3550 +/- 500 cm(-1), respectively. Density functional theory calculations predict values of 2090 and 2265 cm(-1), respectively.