Observation of Anisotropic Modification of the Excited State Potential in Benzene

High-resolution soft x-ray absorption spectra for the C 1s- > pi * transition were measured in C sub 6 H sub 6 and C sub 6 D sub 6 . We observed a complex vibrational structure composed of four major features A, B, C, and D. Peak A corresponds to the photoexcited molecule in its vibrational ground state. In C sub 6 and H sub 6 , the energy positions relative to peak A for peaks B, C and D are 110 +- 10 meV, 181 +- 5 meV, 415 +- 10 meV, respectively. The same excitations are observed in C sub 6 D sub 6 at 70 +- 10 meV, 176 +- 5 meV and 298 +- 5 meV.