2011 Volume 84 Issue 11 Pages 1151-1168
Static structures and dynamics of Ar atom migration in phenol/Ar clusters were investigated by using multiresonance laser spectroscopies which employ more than 3 lasers simultaneously. In the neutral ground state, phenol/Ar (1:1–4) clusters were found to adopt π-bound structure in which all Ar atoms attach to the π-cloud of benzene ring. By considering frequencies of electronic transitions of each cluster, additive rules were found, which suggest that phenol/Ar (1:2–4) clusters adopt (1|1), (3|0), and (3|1) structures, where the notation of (m|n) means that the benzene ring is wedged between m Ar atoms and n Ar atoms. On the other hand, H-bound structure, in which one Ar atom attaches to the end of an OH bond, forms in the cationic ground state generated by laser ionization of the neutral phenol/Ar clusters. According to the principle of vertical ionization, the structures just after the ionization should be π-bound structures, thus this result suggests that one Ar atom migrates from the top of a benzene ring to the end of an OH bond after the ionization. To confirm the existence of such π → H isomerization in cationic state, picosecond time-resolved IR spectroscopy was applied to phenol/Ar (1:2) cluster cation. By measuring the time-resolved IR spectra of OH stretching vibration, the π → H isomerization was successfully observed and found to be an elementary reaction with a time-constant of ≈7 ps. In addition, dynamic peak shift and broadening of the H-bound OH stretching band were observed and interpreted by a simple intramolecular vibrational redistribution (IVR) model.
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