Core-shell photoabsorption and photoelectron spectra of gas-phase pentacene: Experiment and theory
Author(s)
Date Issued
2005
Type
article
Volume
122
Journal
Journal of Chemical Physics
Abstract
The C K -edge photoabsorption and 1s core-level photoemission of pentacene (C22 H14) free molecules are experimentally measured, and calculated by self-consistent-field and static-exchange approximation ab initio methods. Six nonequivalent C atoms present in the molecule contribute to the C 1s photoemission spectrum. The complex near-edge structures of the carbon K -edge absorption spectrum present two main groups of discrete transitions between 283 and 288 eV photon energy, due to absorption to π* virtual orbitals, and broader structures at higher energy, involving σ* virtual orbitals. The sharp absorption structures to the π* empty orbitals lay well below the thresholds for the C 1s ionizations, caused by strong excitonic and localization effects. We can definitely explain the C K -edge absorption spectrum as due to both final (virtual) and initial (core) orbital effects, mainly involving excitations to the two lowest-unoccupied molecular orbitals of π* symmetry, from the six chemically shifted C 1s core orbitals. © 2005 American Institute of Physics.