Lattice vibrations of 1,2,4-triazole

Abstract

The far-infrared spectra of polycrystalline 1,2,4-triazole (C₂N₃H₃) and 1-2-4-[²H₃]triazole have been recorded between 250 and 20 cm^–1. Raman spectra have also been measured. The assignments of the observed frequencies to translatory and rotatory lattice modes were made on the basis of isotopic shift factors. While all the predicted 15 infrared-active lattice modes were identified, only 10 Raman-active modes were observed. The spectra seem to distinguish between the two probable crystal structures (Pbca, P2₁2₁2₁) and the results are consistent with D⁴₂ symmetry with four molecules per unit cell.

The effects of temperature on the lattice vibrational infrared bands have also been studied from room temperature (∼300 K) to liquid nitrogen temperature (∼77 K). The results indicate crystal reorientation with the molecules completely ordered at about –120°C in the unit cell.