LIFETIME OF THE BENZENE DIMER IN THE S-2 ELECTRONIC-STATE

The lifetime of the benzene dimer in the S-2 state has been determined directly by pump-probe measurements with 160 fs laser pulses. The val ue of approximate to 40 fs obtained characterises the fast internal co nversion to the S-0 as well as to the S-1 state. The probability of th e S-2 to S-1 state conversion for the dimer is small but significant a nd a factor of about 2 larger than that for the benzene monomer. These results explain in a direct manner corresponding experiments with ns laser pulses where two-photon enhancement of the ion yield is observed only when the second photon has sufficient energy to ionise the S-1 s tate.