Inner-shell excitation of formaldehyde, acetaldehyde and acetone studied by electron impact

Excitation and ionisation of the carbon and oxygen 1s electrons of formaldehyde, acetaldehyde and acetone have been examined by small-angle inelastic scattering of 2.5-keV electrons, with energy resolutions in the range 0.20-0.50 eV FWHM. Features in the electron energy loss spectra below the inner-shell ionisation thresholds have been assigned to transitions to unoccupied valence (π*) and Rydberg orbitals. Broad maxima in the inner-shell continua of all three molecules have been interpreted as resonances associated with transitions to sigma*(C-O) orbitals. The assignments of the acetaldehyde and acetone spectra have been supported by comparison with those for CH4 and H2CO. The adiabatic first ionisation potentials of H2NO and H2CF have been estimated from the inner-shell spectra of formaldehyde using the equivalent-core analogy. (orig.)