title: Hydrogen bonds and ionic forms versus polymerization of imidazole at high pressures.
abstract: Imidazole (C3H4N2) is an important biomaterial for material research and applications. Our high-pressure Raman spectroscopic investigations combined with ab initio calculations on crystalline imidazole suggest that C-H---X (X = N, π) and N-H---N intermolecular hydrogen bonding interactions largely influence the nature of its structural and polymeric transformations under pressure. At pressures around ∼10 GPa, the reduction in the N---N distances close to the symmetrization limit and the emergence of the spectral features of the cationic form indicate the onset of proton disorder. The pressure-induced strengthening of the "blue-shifting hydrogen bonds" C-H---X (X = N, π) in this compound is revealed by the Raman spectra and the ab initio calculations. No polymer phase was retrieved on release from the highest pressure of 20 GPa in this study.
authors.affiliation: High Pressure & Synchrotron Radiation Physics Division, Bhabha Atomic Research Centre , Mumbai 400 085, India.
authors.forename: Bharat Bhooshan
authors.initials: BB
authors.lastname: Sharma
authors.forename: Ashok K
authors.initials: AK
authors.lastname: Verma
authors.forename: Susy
authors.initials: S
authors.lastname: Thomas
authors.forename: Chitra
authors.initials: C
authors.lastname: Murli
authors.forename: Surinder M
authors.initials: SM
authors.lastname: Sharma
mesh_terms: D006860:Hydrogen Bonding; D007093:Imidazoles / Q000737:chemistry*; D007477:Ions / Q000138:chemical synthesis / Q000737:chemistry; D058105:Polymerization; D011312:Pressure; D011789:Quantum Theory; D013059:Spectrum Analysis, Raman
chemical_list: D007093:Imidazoles; D007477:Ions; C029899:imidazole