9 GHz CW-EPR molecular dynamics study of polycrystalline 1-benzyl 4-hydroxy piperidine

• Published in: Physica. B, Condensed matter Condensed matter, 1998-09, Vol.252 (4), p.262-267
• Main Authors: Krzyminiewski, R, Pawlicka, M, Kruczynski, Z, Kudynska, J, Buckmaster, H.A
• Format: Article
• Language: English
• Subjects: Acceptor–bridge–donor; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Electron delocalization; Electron paramagnetic resonance and relaxation; EPR; Exact sciences and technology; Free radicals; Lattice dynamics; Magnetic resonances and relaxations in condensed matter, mössbauer effect; Other topics in lattice dynamics; Phase transition; Physical radiation effects, radiation damage; Physics; Piperidine; Structure of solids and liquids; crystallography; γ ray effects
• ISSN: 0921-4526; 1873-2135
• DOI: 10.1016/S0921-4526(98)00195-1

This paper reports the results of a 9.4 GHz CW-EPR study of the molecular dynamics in a polycrystalline sample of 1-benzyl 4-hydroxy piperidine which was γ-irradiated with a 150 kGy dose at 293 K. The temperature dependence of the hyperfine splitting (HFS) and spectral line width was measured in this acceptor–bridge–donor molecular structure from 123–273 K. A model evaluation procedure was used to determine the best–fit simulation of the observed spectrum. It was concluded that the ionizing radiation generates a free radical (I) by removal of one hydrogen from the CH 2 group in the bridge connecting the benzene and piperidine rings and another free radical (II) by breaking the bond between the carbon and hydrogen atoms in the piperidine ring. The HFS parameters and the unpaired electron densities were determined. The line width for radical (I) was found to be temperature dependent with an anomaly near 190 K indicative of either a solid–solid structural phase transition or conformational changes and did not saturate at microwave cavity input power levels up to 7 mW. The HFS parameter for radical (I) was also found to be temperature dependent between 123 and 273 K with an anomalous peak near 190 K in agreement with that observed for the line width.