Conformational study of jet-cooled L-phenylglycine.

We investigated the conformational structures of L-phenylglycine in the gas phase by photoionization and double resonance spectroscopy techniques as well as high-level ab initio calculations. The UV-UV and IR-UV double resonance spectroscopy suggested that there exists only one conformer that has a free OH band for the carboxyl group. Rotational contour analysis combined with ab initio calculation indicated that the conformer we detected by resonant two-photon ionization was not one of those found by Sanz et al. in their microwave spectroscopic study [Chem. Eur. J. 12, 2564 (2006)]. Different methods of vaporization along with different expansion and cooling conditions and different detection methods are believed to be the culprit for such intriguing discrepancy. The identical hydrogen bonding structure of our phenylglycine conformer with the most abundant conformer of glycine found in helium droplets and their nearly identical OH frequencies suggest that the skeletal structure of glycine is not significantly altered by phenyl substitution.