An experimental and theoretical study of the electronic structure of copper phthalocyanine (CuPc) molecule is presented. We performed x-ray photoemission spectroscopy (XPS) and photoabsorption [x-ray absorption near-edge structure (XANES)] gas phase experiments and we compared the results with self-consistent field, density functional theory (DFT), and static-exchange theoretical calculations. In addition, ultraviolet photoelectron spectra (UPS) allowed disentangling several outer molecular orbitals. A detailed study of the two highest occupied orbitals (having a(1u) and b(1g) symmetries) is presented: the high energy resolution available for UPS measurements allowed resolving an extra feature assigned to vibrational stretching in the pyrrole rings. This observation, together with the computed DFT electron density distributions of the outer valence orbitals, suggests that the a(1u) orbital (the highest occupied molecular orbital) is mainly localized on the carbon atoms of pyrrole rings and it is doubly occupied, while the b(1g) orbital, singly occupied, is mainly localized on the Cu atom. Ab initio calculations of XPS and XANES spectra at carbon K edge of CuPc are also presented. The comparison between experiment and theory revealed that, in spite of being formally not equivalent, carbon atoms of the benzene rings experience a similar electronic environment. Carbon K-edge absorption spectra were interpreted in terms of different contributions coming from chemically shifted C 1s orbitals of the nonequivalent carbon atoms on the inner ring of the molecule formed by the sequence of CN bonds and on the benzene rings, respectively, and also in terms of different electronic distributions of the excited lowest unoccupied molecular orbital (LUMO) and LUMO+1. In particular, the degenerate LUMO appears to be mostly localized on the inner pyrrole ring.
Abstract. Supersonic beams of oxygen, nitrogen, and chlorine atoms and of metastable oxygen and nitrogen molecules produced from a high-pressure radiofrequency discharge beam source have been characterized by coupling velocity selection with magnetic analysis in the transmission mode. The present work leads to the determination of the relative populations of the electronic states of the species in the produced beams, showing that estimates of the populations from plasma temperatures or final translational temperatures could bring on incorrect conclusions.
We report high resolution measurements of near edge X-ray absorption fine structure spectra (NEXAFS) at the carbon and oxygen K edges of the series of related organic molecules acetaldehyde, acetone, formic acid, methanol, dimethyl ether, and paraldehyde. The spectra are compared with previous measurements of these gases and formaldehyde and with theoretical calculations. Much more fine structure is resolved than previously, particularly at the carbon edge. The results are in good overall agreement with the theoretical predictions of Plashkevych et al. (Chem. Phys. 2000, 260, 11) that the methyl group spectrum is relatively independent of the functional groups to which it is bonded, as are the carbon and oxygen carbonyl group spectra. On the other hand, oxygen atoms in hydroxyl and ether groups are strongly influenced by neighboring atoms. All of the carbon edge spectra investigated show fine structure, and only in the case of acetone do the density of states and number of vibrational degrees of freedom begin to obscure fine detail. The term values of the strongest transitions to states of acetaldehyde and acetone at the C 1s and O 1s edges are in reasonable agreement with theoretical calculations. The splittings of the C 1s -1 3p(CH 3 ) and 3p(CO) Rydberg states due to the low symmetry of the molecules are 0.6-0.7 and 0.38 eV for both molecules, in good agreement with theory. Absolute values of the photoabsorption cross-section, where available in the literature, show moderate to very poor agreement with measured values.
The C K-edge photoabsorption and 1s core-level photoemission of pentacene (C22H14) 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 pi* virtual orbitals, and broader structures at higher energy, involving sigma* virtual orbitals. The sharp absorption structures to the pi* 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 pi* symmetry, from the six chemically shifted C 1s core orbitals.
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