Symmetry rhomboidal

Penrose tiling with a fivefold symmetry axis consisting of two kinds of rhomboid tiles... 

Rhombic prism lattice, 8 114t Rhombohedral structure, of ferroelectric crystals, 11 95, 96 Rhombohedron lattice, 8 114t Rhomboidal symmetry, 8 114t Rhone-Poulenc process, 24 482, 485 Rhovanil extra pure vanillin, 25 548t, 549-550... 

Infrared absorption spectra have been measured for NaF and KF isolated in solid argon. The fundamental modes of these species and the B3u, B2u, and Blu modes of (NaF)2 and (KF)2 are assigned assuming a planar rhomboid structure of D2h symmetry for the dimers.171 Surface ionization of lithium and its halides has been studied by a double-filament technique. At relatively high temperatures the temperature dependence of the lithium surface ionization current from all molecules studied was identical with that from lithium. Incomplete dissociation of LiCl can account for Li ionization threshold temperatures well above that for surface ionization of Li atoms. Dissociation energies of 4.8 0.1 eV for LiCl(g) and 4.3 0.1 eV for LiBr(g) were obtained.172 The equilibrium ionic forms in salt vapours have been studied. The concentration of M+ and X ions in the saturated vapours of MX (M = Na or K, X = halogen) at 850 °C is 107—1010 ions cm-3 and the concentration of M2X+ and M2X ions is 109—1011 ions cm-3, so that the vapours exhibit measurable electric conductivity. The equilibrium constants for the gaseous reactions are as follows ... 

Various other symmetries of the tetranuclear species give rise to different Hamiltonians. One particularly useful Hamiltonian, which essentially results from rhomboidal symmetry, is in Eq. (3). In this Hamiltonian, the diagonal exchange constants are nonequal and different from the exchange between the ions around the periphery. 

The routines, given later, have been written in Microsoft BASIC and use arrays to store the calculated parameters. In these subroutines, the variables CO and NALPHA are given by Nf3 /3k and x(TIP) (temperature-independent paramagnetism), respectively. These subroutines can be used in conjunction, for instance, with a spreadsheet to quickly work out a new system or to check out one in the literature. As an example of the latter, we take a very recent case of rhomboidal symmetry found by Chaudhuri et al. (54) in a butterfly complex in which the body ions are Mn with Sj = S3 = 2, and the wing-tips are Cr , with S2 = S4 = f. The lowest two coupled states found for best fit and given in Fig. 4 of Chaudhuri et al. (54) are 3, 3, 0) (ground) and 2, 3, 1) separated by 15.8 cm Use of Eq. (10) shows the following ... 

The implication was that, if the transition state is provisionally assumed to have D4/1 symmetry, it should be stabilized by relaxation along a 62 coordinate (in the axis convention of Fig. 8.12) towards rhomboidal (D ) geometry. Three multi-configurational computations appeared soon thereafter [57, 58, 59], all indicating that the transition state is indeed square-planar, though the restoring force to the rhombic displacement was extremely small [59] in one... 

Fig. 6 Ground and excited potential energy surfaces along the rhomboidal distortirai in Mo2(DXyIF)2(02CCH3)2(p2-0)2 us calculated by CASSCF. A pseudo-Jahn-Teller mixing of ground and excited (ltd ) states causes the molecule to adopt a lower symmetry structure.

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