Vibrational effects on the valence electronic structure of acetaldehyde: An electron momentum spectroscopy investigation

We report an electron momentum spectroscopy investigation on the valence electronic structure of an important interstellar organic molecule acetaldehyde. The electron momentum profiles are measured using a high-sensitivity angle and energy dispersive multichannel electron momentum spectrometer at incident energy of 1200 eV plus the binding energy. The measurements are compared with the theoretical calculations by density functional theory (B3LYP) and Hartree-Fock method with 6-311++G** and aug-cc-pVTZ basis sets carried out at the equilibrium molecular geometry and by considering vibrational effects. The results exhibit significant influence of nuclear vibrational motion on the momentum profiles for valence orbitals of acetaldehyde, especially 2a '', 8a ' and 1a '' orbitals. Analysis of contributions of individual vibrational normal modes shows that CH3 ddeform mode nu(5) and CH3 d-stretch mode nu(11) play dominant roles. In addition, a (6a ')(-1) satellite state at similar to 20.8 eV is observed.