DIAGONAL 2PH-TDA GREENS-FUNCTION SIMULATION OF THE VALENCE X-RAY PHOTOELECTRON-SPECTRA OF CYCLOALKANES - A THEORETICAL SEARCH FOR SIGNATURES OF THE MOLECULAR-STRUCTURE

With the aim of searching for conformational signatures and investigating tie influence of cyclic connectivity in the valence XPS spectra of cycloalkane compounds ranging from C5H10 to C10H20, the XPS spectra of optimized model structures are simulated by means of the direct Green's function approach. Calculations are performed using the minimal STO-3G basis set and a self-energy expansion derived at the level of the diagonal two-particle-hole Tamm-Dankoff approximation (2ph-TDA). A. bent n-alkane chain is used to decouple roughly the combined effects of the cyclic connectivity and the torsional constraints imposed by such a connectivity. Pseudorotational series are likely to be distinguished from their XPS spectra, as these exhibit slight but significant signatures for ring inversions, which find their origin in the alteration of stabilizing interactions of hyperconjugational character. On the other hand, XPS spectra do not in general disclose a specific fingerprinting of the successive conformations in a given pseudorotational series.