VIBRATIONAL FORCE-FIELD OF ZINC TETRAIMIDAZOLE FROM INELASTIC NEUTRON-SCATTERING

Inelastic neutron scattering measurements have been performed on zinc tetraimidazole tetrafluoroborate and zinc tetraimidazole perchlorate a t 20 K. Only small differences in the vibrational frequencies of the t wo salts were found for the 150 --> 1800 cm(-1) region of the spectrum . Below 150 cm(-1) the differences in the two spectra were associated with ring torsion and lattice modes. Significant differences between t he spectra of the salts and pure imidazole were found for the out of p lane nitrogen-hydrogen modes which are associated with differences in the hydrogen bonding. All low and high frequency modes have been assig ned. It is shown that an isolated molecule normal mode approach is suc cessful in predicting the proton weighted vibrational density of state s for this thirty seven atom cluster and a full harmonic force field h as been established for the perchlorate salt. Variances in interatomic path lengths have been calculated for 20 and 300 K and are found to c ompare favorably with values established from other techniques.