Vibrational relaxation in ground state p-difluorobenzene: Single level preparation by stimulated emission pumping

We have measured the cross section for vibrational relaxation from the 52302 level (εvib = 2036 cm−1) of S0 p-difluorobenzene (pDFB) due to pDFB-pDFB collisions. Stimulated emission pumping has been used to selectively populate the 52302 level. Single vibronic level fluorescence from the S1 level 302, generated by exciting the 5023022 transition at a variable delay time after 52302 has been populated, has been used to monitor the population dynamics of 52302. We obtain a value of 4±1×107s−1 Torr−1 for the vibrational relaxation rate coefficient, a value which is 2–3 times the hard sphere value. This large cross section is consistent with the cross sections observed in S1 benzene but is an order of magnitude larger than the cross sections observed previously for a variety of molecules in the ground electronic state. (AIP)