title: Raman scattering studies on n-heptane under high pressure.
abstract: High-pressure Raman scattering studies at ambient temperature are performed on n-heptane. We observe a liquid-solid transition around 1.5 GPa from the changes in the Raman spectra. This has been reported in earlier works. With increasing pressure, we observe large changes in the Raman modes and the spectra show a distinct change around 7.5 GPa. This marks the solid-solid transition at 7.5 GPa observed in n-heptane for the first time. As predicted in theoretical work, we observe dampening of methyl rotation in n-heptane below 7.5 GPa. With increase in pressure above 7.5 GPa we observe a definitive conversion of gauche to trans conformation in the solid phase. Upon release of pressure we do not observe any hysteresis, which suggests that the solid-solid transition takes place with no volume change or is a second-order transition. In this paper we propose this transition to be an orientational order-disorder transition driven by the dampening of the rotation of the methyl group.
authors.affiliation: Chemistry and Physics of Material Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur P.O., Bangalore 560 064, India.
authors.forename: G
authors.initials: G
authors.lastname: Kavitha
authors.forename: Chandrabhas
authors.initials: C
authors.lastname: Narayana
mesh_terms: D006536:Heptanes / Q000737:chemistry*; D007834:Lasers; D008027:Light; D011312:Pressure; D012015:Reference Standards; D012542:Scattering, Radiation; D012680:Sensitivity and Specificity; D013059:Spectrum Analysis, Raman / Q000379:methods* / Q000592:standards; D014732:Vibration
chemical_list: D006536:Heptanes; C028618:n-heptane