Near ultra-violet absorption spectrum of crystalline benzoxazole in polarized light

Abstract

The absorption anisotropy of crystalline benzoxazole in the region 35 000-40 000 cm^–1 is investigated from room temperature down to 40 K. Results of the vibrational analysis are compared to those previously obtained in the vapour. Two new excited state frequencies 850 cm^–1 and 196 cm^–1, possibly of A″ symmetry, and two lattice modes, 48 and 83 cm^–1 are evidenced. For the origin of the transition a Davydov splitting of 50 cm^–1 is invoked. Changes in frequency and absorption intensity with temperature are discussed. Optical and spectroscopic data lead to the inference that the benzoxazole crystal belongs to the C⁵_2h(P2_1/c) space group, with four molecules per unit cell.