document: The vibrational spectra of l-cysteine have been recorded and assigned in both solution [8,9] and the solid state [10–14]. Spectral assignments have been made using empirical force fields [15], Hartree–Fock calculations [10,16,17] based on the isolated molecule approximation. For systems that exhibit strong intermolecular interactions, this approximation often leads to poor agreement between experiment and theory. A striking example is purine [18], where a study of the solid state vibrational spectra by isolated molecule and periodic calculations, gave almost quantitative agreement between theory and experiment for the latter, whereas the former gave only modest agreement and was unable to distinguish between the tautomers. In the present case, where the structure consists of ions linked by hydrogen bonds, periodic calculations based on the complete primitive cell are essential [19]. The only work [20] that includes some solid state effects used molecular dynamics but from which it is difficult to extract assignments. The aim of this paper is to provide a complete assignment of the vibrational spectra of l-cysteine in both the orthorhombic and monoclinic forms by the use of a combination of computational and experimental methods.
extractive_keyphrases: complete primitive cell computational and experimental methods empirical force fields hartree–fock calculations hydrogen ions isolated molecule and periodic calculations isolated molecule approximation molecular dynamics periodic calculations purine spectral assignments study of the solid state vibrational spectra tautomers
abstractive_keyphrases: l-cysteine provide a complete assignment of the vibrational spectra of l-cysteine