Structures of the S 1 and T 1 states of benzil are examined based on the experimental results from nanosecond time-resolved infrared spectroscopy and picosecond time-resolved Raman spectroscopy. Nanosecond time-resolved infrared spectra of the T 1 state of benzil as well as its three isotopically substituted analogues were measured in carbon tetrachloride. The observed infrared bands of T 1 benzil were assigned based on the frequency shifts on isotopic ( 18 O, and deuteration) substitutions. The infrared band at 1312 cm 21 is assigned to the CyO anti-symmetric stretch vibration. An infrared band that has large contribution from the central C-C stretch is not observed. Picosecond time-resolved resonance Raman spectra of the S 1 state of benzil were also measured. It has been reported that after the photoexcitation, the benzil molecule shows an ultrafast conformational change in the S 1 state. The observed resonance Raman bands are attributable to the vibrations of the relaxed form of the S 1 state. By comparing the Raman and infrared spectra of the S 0 , S 1 , and T 1 states of benzil, the structures of benzil in the excited states are discussed. Upon going from the S 0 state to the S 1 or T 1 state, the bond order of the CyO bond decreases while that of the central C-C bond increases. Although several ground-state bands appear in both the infrared and Raman spectra, there is no band observed simultaneously in the infrared and Raman spectra of the T 1 state, except for bands attributable to the phenyl ring vibrations. We conclude that T 1 benzil has the inversion center that arises from the trans-planar structure. The spectral pattern of the resonance Raman scattering of the relaxed S 1 state is very similar to that of the T 1 state. This implies that the molecular structure of the relaxed S 1 state is similar to that of the T 1 state. The structure of the relaxed form of the S 1 state is also considered to be trans-planar.