Short-range interactions within molecular complexes formed in supersonic beams: Structural effects and chiral discrimination

One- and two-color, mass-selected R2PI spectra of the S-1 <-- S-0 transitio ns in the bare chiral chromophore R-(+)-1-phenyl-1-propanol (R) and its com plexes with a variety of alcoholic solvent molecules (solv), namely methano l, ethanol, 1-propanol, 2-propanol, 1-butanol, S-(+)-2-butanol, R-(-)-2-but anol, 1-pentanol. S-(+)-2-pentanol, R-(-)-2-pentanol, and 3-pentanol were r ecorded after a supersonic molecular beam expansion. Spectral analysis, cou pled with theoretical calculations, indicate that several hydrogen-bonded [ R . solv] conformers are present in the beam. The R2PI excitation spectra o f [R . solv] are characterized by significant shifts of their band origin r elative to that of bare R. The extent and direction of these spectral shift s depend on the structure and configuration of solv and are attributed to d ifferent short-range interactions in the ground and excited [R . solv] comp lexes. Measurement of the binding energies of [R . solv] in their neutral a nd ionic states points to a subtle balance between attractive (electrostati c and dispersive) and repulsive (steric) forces, which control the spectral features of the complexes and allow enantiomeric discrimination of chiral solv molecules.