Spectroscopic enantiodifferentiation of chiral molecules in the gas phase

Enantiodiscrimination of several chiral mols., i.e. S-(+)- (s) vs. R-(-)-2-butanol (r) and S-(+)- (s') vs. R-(-)-2-butylamine (r'), is obtained by two-color resonance-enhanced two-photon ionization time-of-flight (2cR2PI-TOF) spectroscopy of their supersonically expanded complexes with a suitable chromophore, i.e. R-(+)-1-phenyl-1-propanol (R). Anal. of the 2cR2PI-TOF excitation spectra indicates that these complexes are formed in the supersonic beam in several isomeric hydrogen-bonded structures. The different bathochromic shifts of the band origin regions of the mol. diastereomeric complexes relative to that of bare R provide a viable means for spectroscopically discriminating the enantiomers. A further tool for their differentiation is provided by the very reproducible differences in the mass spectral fragmentation patterns of the jet-cooled diastereomeric aggregates.