Valence (chemistry)

About: Valence (chemistry) is a research topic. Over the lifetime, 24937 publications have been published within this topic receiving 645252 citations. The topic is also known as: valency.

Abinitio configuration interaction study of the valence states of O2

Abstract: Configuration interaction calculations have been performed for the 62 electronic states of O2 arising from O atoms in the lowest 3P, 1D, and 1S states. The calculations used an extended one‐particle basis set, and included internal and semi‐internal electron correlation effects. Numerical values for potential curves are reported for all states. Detailed comparison with experiment and other calculations is made for the seven lowest bound states: X 3Σg−, a 1Δg, b 2Σg+, c 1Σu−, C 3Δu, A 3Σu+, and B 3Σu−. For these seven states the maximum error in the calculated spectroscopic constants Re, De, Te, and ωe are 0.04 A, 0.4 eV, 0.2 eV, and 120 cm−1, respectively.

Femtosecond x-ray spectroscopy of an electrocyclic ring-opening reaction

Abstract: The ultrafast light-activated electrocyclic ring-opening reaction of 1,3-cyclohexadiene is a fundamental prototype of photochemical pericyclic reactions. Generally, these reactions are thought to proceed through an intermediate excited-state minimum (the so-called pericyclic minimum), which leads to isomerization via nonadiabatic relaxation to the ground state of the photoproduct. Here, we used femtosecond (fs) soft x-ray spectroscopy near the carbon K-edge (~284 electron volts) on a tabletop apparatus to directly reveal the valence electronic structure of this transient intermediate state. The core-to-valence spectroscopic signature of the pericyclic minimum observed in the experiment was characterized, in combination with time-dependent density functional theory calculations, to reveal overlap and mixing of the frontier valence orbital energy levels. We show that this transient valence electronic structure arises within 60 ± 20 fs after ultraviolet photoexcitation and decays with a time constant of 110 ± 60 fs.

The Chemical Bond between Au(I) and the Noble Gases. Comparative Study of NgAuF and NgAu+ (Ng = Ar, Kr, Xe) by Density Functional and Coupled Cluster Methods

Abstract: The nature of the chemical bond between gold and the noble gases in the simplest prototype of Au(I) complexes (NgAuF and NgAu+, where Ng = Ar, Kr, Xe), has been theoretically investigated by state of art all-electron fully relativistic DC-CCSD(T) and DFT calculations with extended basis sets. The main properties of the molecules, including dipole moments and polarizabilities, have been computed and a detailed study of the electron density changes upon formation of the Ng−Au bond has been made. The Ar−Au dissociation energy is found to be nearly the same in both Argon compounds. It almost doubles along the NgAuF series and nearly triples in the corresponding NgAu+ series. The formation of the Ng−Au(I) bonds is accompanied by a large and very complex charge redistribution pattern which not only affects the outer valence region but reaches deep into the core−electron region. The charge transfer from the noble gas to Au taking place in the NgAu+ systems is largely reduced in the fluorides but the Ng−Au chemic...

Electronic structure of Ni and Pd alloys. I. X-ray photoelectron spectroscopy of the valence bands

Abstract: X-ray photoelectron (XPS) spectra of the valence bands of approximately 60 Ni and Pd alloys and intermetallic compounds with 20 different elements are presented. In alloys with electropositive elements the Ni and Pd $d$-band centroids move to larger binding energies and the density of $d$ states at the Fermi level (${E}_{F}$) is greatly decreased, indicating that the Ni and Pd $d$ bands are being filled. The Ni and Pd $d$ bands become narrower in alloys with electropositive elements. It is shown that in such alloys, the Ni-$M$ or Pd-$M$ interactions give a significant contribution to the Ni and Pd bandwidths. This contribution is larger when the second element $M$ has a large density of states at the energy of the Ni or Pd $d$ bands in the alloy. As this contribution is small in systems that form complicated structural types and glasses we speculate that its absence helps stabilize such structures. The satellite at \ensuremath{\sim}6 eV in the XPS spectrum of Ni is found to weaken and shifts to higher binding energy in alloys with electropositive metals. In the twelve alloys where its intensity is large enough to allow us to identify its energy, the binding energy of the satellite agrees with the two-electron binding energy of the Ni $^{1}G {d}^{8}$ term derived from Auger spectroscopy. The site- and symmetry-selected densities-of-states curves were calculated for 14 of the alloys to show that this filling is largely due to changes in the hybridization of the Ni or Pd $d$ bands with the partner element bands. The actual transfer of Ni and Pd $d$ electrons is probably small. These observations are used to rationalize published results of specific-heat and magnetic measurements on such alloys.