Coordinate ridge

Oak Ridge Associated Universities Panel for the Committee on Interagency Radiation Research and PoHcy Coordination, Health Effects ofEow Frequemy Electric and Magnetic Fields, Washington, D.C., June 1992. 

The geometrical properties of the PES in the vicinity of a transition state mean that the steepest descent path down from the transition state (also generally calculated in mass-weighted coordinates, and called the intrinsic reaction coordinate or IRC) will usually lead only to a single reactant in one direction and a single product (or intermediate) in the other. However, a transition state can sometimes be shared by more than one reactant and/or product. One of these cases arises when the PES possesses a so-called valley-ridge inflection point (VRI). °... 

RDGmcpd has split into two new ridges (comprising the MCPD valley ) around 1.0 amu1/2bohr from the decay point (see Figure 17). Distances are measured in mass-weighted Cartesian coordinates as defined in Ref. 81. 

Figure 5.34 Relief plot of the Coulomb potential energy term V= — C(a, 12)/R for a two-electron-one-ion system, given in the hyperspherical coordinates a, 12, and R. The potential is shown for Z = 1 and R = 1. The centre of the saddle-shaped potential is the Wannier point located at a = 45°, l2 = 180° and V = — 2.12 au. Other characteristic features are the Wannier ridge (a = 45°), the two infinitely deep troughs at a = 0° and a = 90°, and the two infinitely high towers at 12 = 0° and l2 — 360°. From [Eic90], see...

At the (100) surface of MgO, the ions are pentacoordinated this high coordination decreases the reactivity. In this surface, the oxygen dianions are less reactive than those at the protruded ridges of the TiO2(110) surface that are dicoordinated. MgO is less basic than Ti02-... 

For instance, the Til atom has a three-fold co-ordination by oxygen on the facet ridges, as opposed to bulk co-ordination. In the final model, a surface octahedral interstitial site of the O lattice was found to be occupied by a surface titanium atom, with 40% occupancy per (1x3) cell. Partial occupancies of 60% were also found for the 01 and Ti5 surface atoms. The resulting stoiehiometry for this surface structure is TiOi.es, which is equivalent to a 15.5% oxygen deficiency on the surface relative to the bulk. Hence, the refined model can be described as the formation of strongly distorted 110 micro facets on the surface with oxygen defects and a partial occupancy of an interstitial site. Relaxations are found down to 9 A below the topmost layer. The different coordinations found for Ti might explain part of the photo-catalytic properties of this surface. 

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