Inelastic neutron scattering, Raman spectroscopy and periodic DFT study of purine

Abstract

The inelastic neutron scattering (INS) spectrum of purine at 20 K has been recorded and compared to that derived from ab initio DFT calculations for the isolated molecule in both its N7H and N9H tautomers as well as a periodic DFT calculation using the complete unit cell. For the isolated molecule calculations modest agreement is found for the N7H tautomer and poor agreement with the N9H tautomer consistent with the known crystal structure. Much better agreement is found with a periodic DFT calculation of the complete unit cell that explicitly includes the intermolecular interactions, in particular, the hydrogen bonding and the factor group splitting. The lattice mode region is observed by INS and Raman spectroscopies for the first time and assignments are made.