Local exterior electron density and molecular orientation reflected in Penning ionization electron spectra: n-alkane mono- and multilayers on graphite

• Published in: Journal of electron spectroscopy and related phenomena 2004-07, Vol.137, p.199-203
• Main Authors: Suhara, Masanori, Ozaki, Hiroyuki
• Format: Article
• Language: English
• Subjects: Local exterior electron density; Molecular orientation; Monolayer; Multilayer; n-Alkane; Penning ionization electron spectroscopy
• ISSN: 0368-2048; 1873-2526
• DOI: 10.1016/j.elspec.2004.02.036

Long n-alkanes “lie” to form mono- and multilayers when vapor-deposited onto a graphite (0 0 0 1) surface cooled adequately. Penning ionization electron spectra (PIES) of these extrathin films exhibit three bands in the C2p-derived molecular orbital (MO) region. The intensity of the third band relative to the first band is always smaller for the multilayers than for the monolayers. Local electron densities of individual MOs oozing from the externally exposed surface of outermost molecules have been calculated for several model surfaces to synthesize PIES theoretically. Comparison between the observed and synthesized PIES discloses the alkane’s manner of “lying” as well as the origins of the PIES bands. The zigzag plane lies flat in the monolayer, but becomes tilted in the multilayer, maintaining the chain direction parallel to the substrate surface. The third band is due to pseudo-π (pπ) MOs alone irrespective of the number of layers. The first and the second band are, however, ascribed to both pπ and σ 2p MOs; two thirds of the intensity of these bands is attributed to pπ MOs in the monolayer but the ratio decreases in the multilayer.