Near edge x-ray-absorption fine-structure determination of alkyl-chain orientation: Breakdown of the building-block scheme

The orientation of hydrocarbon chains deposited on surfaces has been studied by near edge x-ray-absorption fine structure (NEXAFS). The so-called building-block scheme, which is generally used to predict angular dependences of NEXAFS resonances, is found to be inadequate for C-C * resonances in larger molecules, in contrast to previous work [D. A. Outka, J. Stöhr, J. P. Rabe, J. D. Swalen, and H. H. Rotermund, Phys. Rev. Lett. 59, 1321 (1987)]. Using the results of ab initio electronic structure calculations consistent results for several systems containing long hydrocarbon chains could be obtained.