Hydrogen fluoride geometry

The components of the rotational g tensor of hydrogen fluoride, water, ammonia and methane have been calculated at their equilibrium geometries with different correlated ab initio methods and two large basis sets. 

Table 5.15 Comparing Mulliken, electrostatic potential and natural charges, and Mulliken and Lowdin bond orders, at various levels, for hydrogen fluoride. The geometry used in each case corresponds to the method/basis set for that charge or bond order, but any reasonable geometry should give essentially the same results. There are no experimental data...

Concerning ab initio calculations on neutral hydrogen-bonded complexes we consider the simplest example, the hydrogen fluoride dimer (Table 3). Both the equilibrium geometry and energy of interaction strongly depend on the quality of the basis set... 

Legon, A.C., Soper, P.D., and Flygare, W.H. (1981) The rotational spectrum, H-19F nuclear spin-nuclear spin coupling, D nuclear quadrupole coupling, and molecular geometry of a weakly bound dimer of carbon monoxide and hydrogen fluoride. J. Chem. Phys., 74, 4944-4950. 

Hydrogen fluoride (HF) aqueous, pAa, 139 BDE, 76 geometry of, 32 orbital energies, 26 total energy, 29... 

Our next example will be the hydrogen fluoride dimer. It is a good example to show that the electrostatics restricted to the dipole-dipole interaction (or the equivalent charge interaction model) is not sufficient to determine the minimum orientation even for interactions of diatomic monomers. Such a model predicts the linear F-H- -F-H structure dictated by the optimal orientation of the dipoles, which disagrees with the observed structure in which the hydrogen acceptor is tilted away from the linear geometry by about 60°... 

TABLE 9.1. Geometry and Energy of Hydrogen Fluoride Dimer° ... 

In drawing structures for hydrogen (H2) and hydrogen fluoride (HF), it has been possible to account for the location of all (both) of the nuclei in a linear fashion with bonds that are symmetrical about the intemuclear axis (i.e., a bonds). However, with methane, CHi, which cannot be linear, a geometry problem arises. 

Geometry of the hydrogen fluoride dimers. The axis is inclined to the F-F axis by 1.3-pending upon the isotropic species. 2.5° de-... 

In all applications discussed in the following chapters the many-dimensional energy surfaces have been Scanned pointwise as a function of some appropriately chosen set of internal coordinates. Energy values thus obtained have been subjected to polynomial fits in order to find the equilibrium geometry and internal, harmonic force constants. In a few cases (polyyne, hydrogen fluoride, hydrogen cyanide) these force constants have been used for an evaluation of vibrational frequencies and phonon dispersion curves within the framework of the harmonic approximation using standard methods of polymer vibrational spectroscopy (see e.g. refs. l8,19 ). 

Chromium (II) also forms sulfides and oxides. Chromium (II) oxide [12018-00-7], CrO, has two forms a black pyrophoric powder produced from the action of nitric acid on chromium amalgam, and a hexagonal brown-red crystal made from reduction of Cr202 by hydrogen ia molten sodium fluoride (32). Chromium (II) sulfide [12018-06-3], CrS, can be prepared upon heating equimolar quantities of pure Cr metal and pure S ia a small, evacuated, sealed quartz tube at 1000°C for at least 24 hours. The reaction is not quantitative (33). The sulfide has a coordination number of six and displays a distorted octahedral geometry (34). 

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