Photoionization of glycine-betaine: a permanent zwitterion

Abstract The electronic structure of permanent zwitterion, glycine-betaine (GBZW) has been studied using high-level ab initio method: equation-of-motion couple-cluster (EOM-CCSD) method. The photoelectron spectra of GBZW have been simulated in the valence and core ionization regions. The zwitterion shows remarkable stability with standard enthalpy of formation ΔHfo(g) = -313.6 kJ/mol and 1st ionization energy which is 2 eV lower compared to the parent glycine. The results help understanding of molecular structure of ubiquitous zwitterions.