Hydrogen transfer dynamics in a photoexcited phenol/ammonia (1:3) cluster studied by picosecond time-resolved UV-IR-UV ion dip spectroscopy

The picosecond time-resolved IR spectra of phenol/ammonia (1:3) cluster were measured by UV-IR-UV ion dip spectroscopy. The time-resolved IR spectra of the reaction products of the excited state hydrogen transfer were observed. From the different time evolution of two vibrational bands at 3180 and 3250 cm(-1), it was found that two isomers of hydrogenated ammonia radical cluster center dot NH4(NH3)(2) coexist in the reaction products. The time evolution was also measured in the near-IR region, which corresponds to 3p-3s Rydberg transition of center dot NH4(NH3)(2); a clear wavelength dependence was found. From the observed results, we concluded that (1) there is a memory effect of the parent cluster, which initially forms a metastable product, center dot NH4-NH3-NH3, and (2) the metastable product isomerizes successively to the most stable product, NH3-center dot NH4-NH3. The time constant for OH cleaving, the isomerization, and its back reaction were determined by rate-equation analysis to be 24, 6, and 9 ps, respectively.