Vibrational relaxation of OH and OD stretching vibrations of phenol and its clusters studied by IR-UV pump-probe spectroscopy

The vibrational relaxation of the OH/OD stretching mode of phenol and its c luster with Ar or H2O has been observed directly by nanosecond IR-UV pump-p robe spectroscopy. The OH/OD vibrational level was prepared by a tunable na nosecond IR light pulse, and the decay of the pumped level as well as the r ise of the relaxed level were observed by two-photon ionization with a tuna ble UV laser. For the OI-I stretch level of phenol-do, two components were observed: a fast component with a decay time of a few nanoseconds and a slo w component with a decay time longer than 1 mu s. It was also found that th e decay rate of the first component coincides with that of the rise of rela xed levels. The results indicate that the intramolecular vibrational redist ribution (IVR) of the OH stretching vibration of bare phenol-d(0) is classi fied as an intermediate-strong-coupling case. For phenol-d(1), only the slo w component was identified for the decay of the OD stretching vibration, wh ereas the relaxed level showed a rise with a few nanoseconds, similar to th e case of phenol-d(0). In the case of phenol-Ar and phenol-H2O, on the othe r hand, the OH stretching level showed a fast single-exponential decay curv e, indicating a transformation from intermediate coupling to the statistica l limit upon the cluster formation.