Pressure-induced Fermi resonance between fundamental modes in a-Hydroquinone

Fermi resonance (FR), a prevalent phenomenon in molecules, has an important effect in spectrum analysis. As an effective way to change the molecular structure and tune symmetry, high-pressure techniques can often induce FR. Hydroquinone (HQ) is a hydrogen-bonded crystal that tends to form a solid inclusion compound with a suitable guest and has wide applications. In this work, a high-pressure technique was used to investigate a-HQ using high pressure to tune the symmetry to produce FR. Raman and infrared spectra of a-HQ were investigated at ambient pressure, and then Raman spectra under high pressure of a-HQ were investigated up to 19.64 GPa. Results indicated that there were two phase transitions found at about 3.61 and 12.46 GPa. Fundamental FR was not present in a-HQ molecules at ambient pressure. At 3.61 GPa, the first-order phase transition occurred due to the pressure-induced symmetry change, resulting in two Raman modes at 831 cm-1 and 854 cm-1 with the same symmetry, thereby providing evidence that the fundamental FR phenomenon occurred. Furthermore, the pressure-induced changes of the FR parameters were elucidated. Thus pressure provided an effective way to study FR between two asymmetric species.

Automated summary

This study investigated the effect of high pressure on Hydroquinone (HQ) and found that at a pressure of 3.61 GPa, a fundamental Fermi resonance phenomenon occurred due to a symmetry change.