Phase Behavior of <i>n</i>-Alkanes under High Pressure

The effect of pressure on the phase transition behavior of tridecane, pentadecane and heptadecane has been investigated up to 489, 220 and 387 MPa, respectively, using Fourier transform infrared spectroscopy at 25℃. Short range positional order in the rotator phase is discussed on the basis of factor group splitting of the P1+P3 band of the methylene rocking mode. A large proportion of alkane molecules is found to possess herringbone-type short-range positional order in the high pressure rotator phase while a smaller proportion of alkane molecules is considered to possess herringbone-type short-range positional order in the high temperature rotator phase.