Electronic and vibrational structure

Photoelectron spectroscopy (PES, a non-mass spectral technique) [87] has proven to be very useful in providing information not only about ionization potentials, but also about the electronic and vibrational structure of atoms and molecules. Energy resolutions reported from PES are in the order of 10-15 meV. The resolution of PES still prevents the observation of rotational transitions, [79] and to overcome these limitations, PES has been further improved. In brief, the principle of zero kinetic energy photoelectron spectroscopy (ZEKE-PES or just ZEKE, also a nonmass spectral technique) [89-91] is based on distinguishing excited ions from ground state ions. 

Figure 3a. OH energy-level diagram-electronic and vibrational structure...

Optical properties are usually related to the interaction of a material with electromagnetic radiation in the frequency range from IR to UV. As far as the linear optical response is concerned, the electronic and vibrational structure is included in the real and imaginary parts of the dielectric function i(uj) or refractive index n(oj). However, these only provide information about states that can be reached from the ground state via one-photon transitions. Two-photon states, dark and spin forbidden states (e.g., triplet) do not contribute to n(u>). In addition little knowledge is obtained about relaxation processes in the material. A full characterization requires us to go beyond the linear approximation, considering higher terms in the expansion of h us) as a function of the electric field, since these terms contain the excited state contribution. 

The structure of the intermediate implicitly encompasses molecular, electronic, and vibrational components where the molecular structure is most commonly deduced by X-ray crystallography. More limited structural data may also be obtained from solute species through analysis of the X-ray absorption fine structure (XAFS) spectra and this will be discussed briefly in Section 1.6. Clearly the electronic and vibrational structure must be obtained from analysis of the spectra. The interconnection between these aspects of the structure is reinforced by in-silico techniques, where advances in DFT (density-functional theory) have greatly expanded the range of transition-metal compounds and... 

Ultraviolet photoelectron spectroscopy (UPS) of anionic C provides information on the electron affinity (EA), and electronic and vibrational structures of the corresponding neutral species. The size dependence of EAs and the vibrational fingerprints are useful to distinguish isomers when combined with mass spectrometry. In 1988 Yang et al. reported the first experimental indication of the presence of monocyclic carbon clusters C in laser vaporization of graphite in helium gas [17]. For clusters C ... 

Going beyond the narrow framework of electronic structure theory other major challenges become apparent. The rovibrational contributions to NLO properties are known to be significant. This includes both the vibrational averaging as well as pure (ro)vibrational contributions. The development of general, accurate and efficient methods for Are calculation of vibrational contributions is an important area for future research. It requires input from electronic structure calculations and the Aieoretlcal interface between electronic and vibrational structure theory is an Important issue in this research. For a more detailed discussion we refer to a later Chapter of this book. 

The model Hamiltonian of Section II captures some of the essential features of the electronic and vibrational structure of polyatomic molecules, like benzene and 5ym-triazine, that have both nondegenerate and degenerate, Jahn-Teller active, electronic levels. In this section interference experiments are described which will be sensitive to the geometric phase development accompanying adiabatic nuclear motion on either of the electronic potential energy surfaces in the Jahn-Teller pair. 

Ohta, T., K. Matsuura, K. Yoshizawa, and I. Morishima (2000). The electronic and vibrational structures of iron-oxo porphyrin with a methoxide or cysteinate axial ligand. J. Inorg. Biochem. 82, 141-152. 

The electronic and vibrational structure has been investigated using techniques such as ... 

Thereby, the energy distribution of E(e ) can be used to measure the distribution of ionic states produced by photoionization. Typical one photon PES are of sufficient resolution to reveal the vibrational structure, giving information on the electronic and vibrational structure of the ion. The vibronic intensities are usually determined by the Franck-Condon principle, and can often be used to learn about the change in the molecular structure upon ionization. Since the ground state structure is usually well determined by other methods, one photon PES is a valuable tool for the study of the electronic, vibrational and geometrical structure of molecular ions. 

Temperature-dependent electronic and vibrational structure of the l-Ethyl-3-methyhmidazolium Bis(trifluoromethylsulfonyl)amide room-temperature ionic liquid surface a study with XPS, UPS, MIES, and HREELS. 

Ottking, R., Beenken, W.J.D., Hofft, O., Bahr, S., Kenpter, V and Schaefer, J.A., Tenperature-dependent electronic and vibrational structure of the l-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide room-tenperature ionic liquid surface A study with XPS, UPS, MIES, and HREELS, J. Phys. Chem. B 111, 4801-4806 (2007). 

L. Truttmann, K. R. Asmis, and T. Bally, /. Phys. Chem., 99, 17844 (1995). Electronic and Vibrational Structure and Scaled Density Functional Force Field of Cyclopentadiene and Its Radical Cation. 

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