PNNL

Abstract

We report a joint negative ion photoelectron spectroscopy (NIPES) and quantum chemical computational study on glycine-chloride/bromide complexes (denoted Gly·X–, X = Cl/Br) in close comparison to the previously studied Gly·I– cluster ion. Combining experimental NIPE spectra and theoretical calculations, various Gly·X– complexes were found to adopt the same types of low-lying isomers albeit with different relative energies. Despite more congested spectral profiles for Gly·Cl– and Gly·Br–, spectral assignments were accomplished with the guidance from the knowledge learned from Gly·I–, where a larger spin-orbit splitting of iodine afforded well-resolved recognizable spectral peaks. Three canonical plus one zwitterionic isomers for Gly·Cl– and four canonical conformers for Gly·Br– were experimentally identified and characterized in contrast to five canonical ones observed for Gly·I– under similar experimental conditions. Taken together, this study investigates both genericity and variations in binding patterns for the complexes composed of glycine and various halides, demonstrating that iodide-tagging is an effective spectroscopic means to unravel diverse ion-molecule binding motifs for cluster anions with congested spectral bands by substituting the respective ion with iodide.