Conformational Choice, Hydrogen Bonding, and Rotation of the S1 ← S0 Electronic Transition Moment in 2-Phenylethyl Alcohol, 2-Phenylethylamine, and Their Water Clusters

Laser-induced fluorescence and one- and two-color, mass- selected R2PI excitation spectra of the S1 ← S0 electronic transitions in 2-phenylethyl alcohol and 2-phenylethylamine have been recorded in a jet-cooled environment. Five conformers of 2-phenylethyl alcohol and four of 2-phenylethylamine have been identified, together with a number of 1:1 hydrated water clusters. The fifth origin band in the excitation spectrum of 2-phenylethylamine has been reassigned to a water cluster, primarily on the basis of its ion fragmentation pattern. Analysis of their partially resolved rotational band contours has been aided by ab initio molecular orbital calculations, conducted at levels of theory ranging from MP2/3-21G* to MP2/6-311G** for the ground state and CIS/6-311G** for the first electronically excited singlet state. The reliability of the CIS method has also been tested through benchmark calculations, including computations on a related, experimentally known conformational system, methyl 3-hydroxybenzoate. 2-P...