Experimental an d Theoretical Study of Valen ce Photoe lectron Spectrum o f Proline Amino Ac id

The photoele ctron spectroscopy of biological molecules such as amino acids an d nucleotid es in gas phase are very important because the intrinsic properties of amino acids, which are hidden in the complex medium of biological systems, can be understood. In this case, there is a prob ability that amino acids show prope rties which are not observable in t he solution and provide scientific information which creates insight i nto the origi n of physical and che mical properties of biological molecules. In this work, t he valence photoelectro n spectrum of proline in the gas phase has been investig ated by He-I radiation (۲۱.۲۱۸ eV ). Parallel to experiment, the ab i nitio calculations were performed t o estimate the populatio n ratio of proline co nformers a t the temp erature of the experiment and calculate t he photoelectron spectrum of each conformer. Fig. ۱ shows the geo metrical stru ctures of t he four most stable neut ral conformers of the proline molecule in the ga s phase.