How generic is iodide-tagging photoelectron spectroscopy: An extended investigation on the Gly center dot X-(Gly = glycine, X = Cl or Br) complexes

We report a joint negative ion photoelectron spectroscopy (NIPES) and quantum chemical computational study on glycine-chloride/bromide complexes (denoted Gly center dot X-, X = Cl/Br) in close comparison to the previously studied Gly center dot I- cluster ion. Combining experimental NIPE spectra and theoretical calculations, various Gly center dot 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 center dot Cl- and Gly center dot Br-, spectral assignments were accomplished with the guidance of the knowledge learned from Gly center dot I-, where a larger spin-orbit splitting of iodine afforded well-resolved, recognizable spectral peaks. Three canonical plus one zwitterionic isomer for Gly center dot Cl- and four canonical conformers for Gly center dot Br- were experimentally identified and characterized in contrast to the five canonical ones observed for Gly center dot 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.

Automated summary

We conducted a study on glycine-chloride/bromide complexes (Gly center dot X-, X = Cl/Br) using negative ion photoelectron spectroscopy and quantum chemical computations, comparing them with the previously studied Gly center dot I- cluster ion. Through experimental and theoretical analysis, we found that different Gly center dot X- complexes adopt the same types of low-lying isomers with varying relative energies. Despite the congested spectral profiles, spectral assignments for Gly center dot Cl- and Gly center dot Br- were accomplished with the guidance from Gly center dot I-, which has well-resolved spectral peaks. This study investigates the binding patterns of glycine complexes with different halides, demonstrating that iodide-tagging is an effective spectroscopic method for unraveling diverse ion-molecule binding motifs in cluster anions with congested spectral bands.