Journal of Chemical Physics, Vol.103, No.19, 8444-8455, 1995
Vibrational Force-Field of Solid Imidazole from Inelastic Neutron-Scattering
Inelastic neutron scattering (INS) measurements are presented for solid imidazole at 20 K. Both; powder and oriented platelets have been measured. Assignments of bands are consistent with earlier infrared and Raman studies except for a band at 961 cm(-1) which is definitely assigned as A ". A fit with the proton-weighted vibrational density of states is presented and a full harmonic force held has been established. The mean deviation between measured eigenvalues and those predicted from the force field is +/-3 cm(-1). The potential energy distribution is compared to quantum chemistry calculations and is found to be in best agreement with an unscaled calculation [J. Sadlej, A. Jaworski, and K. Miaskiewicz, J. Mol. Struct. 274, 247 (1992)]. The INS spectra from a scaled ab initio force held [K. Fan, Y. Xie, and J. Boggs, Theochem, 29, 339 (1986)] are calculated both before and after refinement against only infrared frequencies and compared to experiment. It is demonstrated that comparison with the INS spectrum is a more stringent test of the force held than. with just the infrared frequencies alone.
Keywords:CRYSTALLINE IMIDAZOLE;LATTICE-VIBRATIONS;INFRARED SPECTRA;NORMAL-MODES;SPECTROSCOPY;ASSIGNMENT;ION