Effect of high hydrostatic pressure on the intramolecular modes of(C59N)2

The effect of high pressure, up to 10 GPa, on the phonon spectra of azafullerene, $({\mathrm{C}}_{59}\mathrm{N}{)}_2,$ at room temperature has been investigated by Raman spectroscopy. At ambient pressure, the Raman spectrum of $({\mathrm{C}}_{59}\mathrm{N}{)}_2$ displays eight of the ten molecular modes of ${\mathrm{C}}_{60}.$ Their frequencies are close to those of the corresponding modes of pristine ${\mathrm{C}}_{60}$ solid. The pressure dependence of the $H_g\mathrm{}\left(7\right),$ $A_g\mathrm{}\left(2\right)\mathrm{}$, and $H_g\mathrm{}\left(8\right)\mathrm{}$ phonon frequencies exhibits reversible changes in their pressure coefficient in the region $6.0\pm 0.5\mathrm{GPa}.$ In addition, the $A_g\mathrm{}\left(1\right)\mathrm{}$ breathing mode shows two clear changes in the pressure dependence of the pressure coefficient, one at ∼3.0 and another at ∼6.0 GPa. The results are explained by taking into account the pressure dependence of the structural properties of solid $({\mathrm{C}}_{59}\mathrm{N}{)}_2.$