Valence–shell electron energy-loss spectra of formic acid and acetic acid

Abstract

Abstract Gas phase optical absorption spectra of formic acid and acetic acid in the energy ranges 5.0–11.3 and 4.4–11.3 eV, respectively, have been previously recorded. It is generally agreed that of the four successive bands observed in the spectra of these compounds, the first corresponds to n → π * transition. However, various assignments have been proposed for the following three bands. In the present study, electron energy-loss spectra of formic acid and acetic acid vapours at 70 eV impact energy and 0° scattering angle have been measured between 5–15 eV. The transition energies that have been observed coincide with those measured by optical methods in the corresponding range. To identify the valence shell transitions among the spectral features observed, the semi-empirical HAM/3 calculations have been performed. With the help of earlier studies on these and related compounds first and third bands are tentatively assigned as valence, whereas second and fourth bands are assigned as Rydberg.