Valence electron momentum spectroscopy of n -butane

• Published in: The Journal of chemical physics 2000-05, Vol.112 (18), p.8043-8052
• Main Authors: Pang, W. N., Gao, J. F., Ruan, C. J., Shang, R. C., Trofimov, A. B., Deleuze, M. S.
• Format: Article
• Language: English
• ISSN: 0021-9606; 1089-7690
• DOI: 10.1063/1.481403

The valence electronic structure and momentum-space electron density distributions of n-butane have been studied by means of high-resolution (e,2e) electron momentum spectroscopy based on noncoplanar symmetric kinematics. Ionization spectra for the range of binding energies 6 to 32 eV and momenta described by azimuthal angles φ=0°, 2°, 4°, 6°, 8°, and 10° have been recorded and compared to the results of one-particle Green’s function calculations, performed using the third-order algebraic–diagrammatic construction [ADC(3)] approximation and series of basis sets of improving quality. Experimental electron momentum profiles have been determined from a set of 11 measurements and compared to theoretical results. It has been shown that despite the complex structure of the spectral bands and the conformational versatility of n-butane, the experimental electron momentum distributions are accurately described by the momentum-space form of orbital densities obtained from Becke three-parameter Lee–Yang–Parr (B3LYP) density functional calculations. Significant broadening of the spectral lines and the s-type angular dependence of their intensities above 24 eV have been explained by the breakdown of the one-electron picture of ionization for the 3ag molecular orbital.