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 ∙ N H 4 ( N H 3 ) 2 coexist in the reaction products. The time evolution was also measured in the near-IR region, which corresponds to 3 p - 3 s Rydberg transition of ∙ N H 4 ( N H 3 ) 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, ∙ N H 4 - N H 3 - N H 3 , and (2) the metastable product isomerizes successively to the most stable product, N H 3 - ∙ N H 4 - N H 3 . 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.