Sub-Doppler high-resolution spectra of benzene: anomalous results in the "channel three" region

We have measured the Doppler-free rotationally resolved two-photon spectrum of two vibronic bands of C6H6,14; 1; and 14; 1:. Compared to the 14; 1; band (E,,,, = 2492 cm-’) a drastically reduced number of sharp is observed in the 14; 1: band (EexCe=88 3 412 cm-’1. The K = 0 rotational lines are still seen, while K #0 lines disappear. This can be understood in terms of Coriolis coupling between the 14l l2 state and other states within Sl and a subsequent nonradiative process. This coupling might be the explanation the drastic onset of line broadening in C6H6 at an excess energy of 3000 cm-l, “channel three”. The line is then due to a different process than that responsible for the population lifetime of S1.