2-DIMENSIONAL FOURIER-TRANSFORM NEAR-INFRARED CORRELATION SPECTROSCOPY STUDIES OF TEMPERATURE-DEPENDENT SPECTRAL VARIATIONS OF OLEYL ALCOHOL

Generalized two-dimensional (2D) correlation spectroscopy has been app lied to the near-infrared (NLR) region for the first time to investiga te temperature-dependent spectral variations of cis-9-octadecan-1-ol ( oleyl alcohol) in the pure liquid state. The 2D correlation spectrosco pic analysis has provided spectral information not readily accessible from conventional one-dimensional spectra. For example, the analysis h as shown that a band at 7090 cm(-1) due to the first overtone of an OH stretching mode of the monomeric alcohol consists of two bands arisin g from the rotational isomerism of the free OH group. The existence of a band due to free terminal OH groups of the linear polymeric species has also been suggested from a synchronous 2D NIR correlation spectru m of the alcohol. An asynchronous 2D NIR spectrum of the alcohol has i ndicated that the pattern of the temperature dependence for the peak i ntensity at 7090 cm(-1) is different from other bands near 6300 cm(-1) attributed to the polymeric forms of the alcohol. The signs of the cr oss peaks indicate that the change (increase) of the peak intensity at 7090 cm(-1) occurs at higher temperature than those peaks at other sp ectral coordinates. It seems, therefore, that the disappearance of the polymeric form does not simultaneously result in the formation of the monomeric form. The polymeric species dissociate into the intermediat e species such as the dimer first, and then the latter breaks down to the monomer. A strong correlation peak appears between two bands at 10 380 and 7090 cm(-1) assignable to the second and first overtones of t he OH stretching mode of the monomeric alcohol, respectively. This obs ervation indicates that the two bands share the identical temperature dependent pattern as expected. The correlation between the bands arisi ng from the same groups of the same species provides an intriguing pos sibility of correlating various overtone and fundamental bands to esta blish unambiguous assignments.