Pressure effect on the Fermi resonance doublets of ν1 ∼ ν12 and ν1+ν6 ∼ ν8 in pyridine

Abstract

Raman spectra of pure pyridine, pyridine aqueous solution, and pyridine in methanol under high pressure were measured separately. Behaviors of two Fermi doublets, v1 and v12, v1+v6 and v8, occurred simultaneously in one pyridine molecule are analyzed according to their spectra, which indicates that the v1 Raman activity decreased with increasing pressure and disappeared eventually, which induced weakness and even disappearance of the Fermi resonance between v1 and v12, while the v1 Raman intensity variation had no effect on the presence of the Fermi resonance between v1+v6 and v8 as well as its variation law with increasing pressure. Those phenomena were interpreted by group theory in this article. It also indicates experimentally that all Raman bands of pyridine appeared blueshift with increasing pressure except that OH group appeared redshift. Moreover, frequency v1 shifted more quickly with increasing pressure than their counterparts did in neat liquid, so did its Raman intensity variation.