Chirality and Intermolecular Forces: Studies using R2PI Experiments in Supersonic Beams

One- and 2-color, mass-selected resonant 2-photon ionization (R2PI) spectra of the S1 S0 transitions in the bare (R)-(+)-1-PhCHMeOH (ER) and its complexes with a solvent mol. [solv: (S)-(+)-butan-2-ol (BS), (R)-(-)butan-2-ol (BR), or water (W)] were recorded after a supersonic mol.-beam expansion. The excitation spectrum of bare ER conforms to theor. predictions at the B3LYP/6-31G** level of theory by pointing to the formation of a single conformer. The 1-color R2PI excitation spectra of the diastereomeric complexes [ER-solv] (solv: BS or BR) are characterized by significant shifts of their band origin relative to that of bare ER. The extent and direction of these spectral shifts depend upon the structure and configuration of solv and are attributed to different short-range interactions in the ground and excited [ER-solv] complexes. By analogy with strictly related diastereomeric complexes, the phenomenol. binding energy of the homochiral [ER-BR] exceeds that of the heterochiral one [ER-BS]. The 1-color R2PI excitation spectra of the [ER-W] complex displays 2 signals blue shifted by 54 and 73 cm-1, relative to the S1 S0 band origin of bare ER, which indicate the presence of a O-H.pi. electrostatic interaction between ER and W.