A HeI photoelectron spectroscopic study of polyunsaturated fatty acids

HeI photoelectron spectra of some unsaturated fatty acids except of docosahexaenoic acid have been observed in the gas phase for the first time, by using an infrared heating device that was developed in this laboratory. The first vertical ionization energies (Iobs) of oleic acid, linoleic acid, linolenic acid, and docosahexaenoic acid have been determined to be 8.85, 8.80, 8.77, and 8.75 eV, respectively. Several higher ionization energies have also been observed. The valence electronic structures associated with the observed ionization energies and the optimum geometries have been elucidated by ab initio calculations carried out in the present study.