Recent Raman and infrared spectra of a number of tetrahalide crystals are reported. While some examples of isotopic and crystal field splittings of the internal molecular modes are included, the emphasis is on the ext...
Recent Raman and infrared spectra of a number of tetrahalide crystals are reported. While some examples of isotopic and crystal field splittings of the internal molecular modes are included, the emphasis is on the external lattice vibrations which are important for investigations of intermolecular forces and lattice dynamics calculations. Because of the weak signals from these non-polar near-spherical molecules and other experimental difficulties, these modes have not been investigated in detail in earlier work. Examples to be discussed include CCl 4 , CBr 4 and CF 4 , all of which exhibit solid state phase transitions; the tetrachlorides of Ge, Ti, Si and Sn, all of which are thought to have similar crystal structures; and SnBr 4 , the structure of which is accurately known and is used as a basis for lattice dynamics calculations.
The equation of motion of a 17-particle chain with anharmonic nearest neighbour forces have been numerically integrated for 101 different initial conditions. The 101 stored histories constitute a constant energy ensem...
The equation of motion of a 17-particle chain with anharmonic nearest neighbour forces have been numerically integrated for 101 different initial conditions. The 101 stored histories constitute a constant energy ensemble. The time dependence of the coarse grained mode Boltzmann H functions indicates that the ensemble evolves reversibly from an initial non-equilibrium state to a final equilibrium state characterized by a minimum in each mode H function. There is no equipartition of energy among the modes.
In recent work on the structure of water I have exploited both time-of-flight neutron diffraction (TOF) and conventional reactor neutron diffraction to extract the hydrogen-hydrogen correlation function in liquid wate...
In recent work on the structure of water I have exploited both time-of-flight neutron diffraction (TOF) and conventional reactor neutron diffraction to extract the hydrogen-hydrogen correlation function in liquid water using the technique of hydrogen/deuterium substitution. Because the dynamic effects on the TOF data have a very different dependence on momentum transfer ( Q ) from those for the reactor data, the two sets of data offer a unique opportunity to establish an estimate of the magnitude of the dynamic correction. Apart from a discrepancy at small Q which is not fully understood at present, the different diffraction techniques show good agreement over most of the Q range. The comparison is used to discuss the applicability of the H/D subtraction (which involves no arbitrary fitting parameters) to molecular liquids in general: the main features in the structure factors can be determined readily. On the other hand, it is likely that finer details such as quantum effects will be obscured by experimental imitations.
NbTe4 is a quasi-one-dimensional metallic compound. The crystal structure is tetragonal and is modulated by an incommensurate distortion wave at room temperature. We show that on the cooling of the crystal into the te...
NbTe4 is a quasi-one-dimensional metallic compound. The crystal structure is tetragonal and is modulated by an incommensurate distortion wave at room temperature. We show that on the cooling of the crystal into the temperature range 100-50 K, two distinct sets of sharp spots can occur along the streaks that arise in the diffraction patterns. There are indications that the two types can occur in different parts of the same crystal. The interpretation of the observations in terms of discommensuration arrays is discussed.
It is demonstrated that the close matching between the minima in the interionic potentials and the maxima of the partial pair-distribution functions, proposed in the literature as a necessary condition for the stabili...
It is demonstrated that the close matching between the minima in the interionic potentials and the maxima of the partial pair-distribution functions, proposed in the literature as a necessary condition for the stability of metallic glasses, does not exactly apply to the transition-metal glasses. In addition, a realistic interionic potential is suggested for the glass-structure calculation.
It is demonstrated that a recently described ab initio variational thermodynamic calculation for pure liquid metals can be significantly improved by using the hard-sphere Yukawa model instead of the usual hard-sphere ...
It is demonstrated that a recently described ab initio variational thermodynamic calculation for pure liquid metals can be significantly improved by using the hard-sphere Yukawa model instead of the usual hard-sphere model as the reference system.
We report the first results of the anodic oxidation of MBE grown on n‐type . The anodic oxide formation occurred at a constant current density of 0.85 mA/cm2 in a tartaric acid ethylene glycol electrolyte at room tem...
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We report the first results of the anodic oxidation of MBE grown on n‐type . The anodic oxide formation occurred at a constant current density of 0.85 mA/cm2 in a tartaric acid ethylene glycol electrolyte at room temperature without external illumination. The oxide growth rate and semiconductor consumption rate were measured to be 1.79 and 1.46 nm/V, respectively. The anodic oxide films were examined using RBS and, within the limitations of backscattering spectroscopy, the oxide was found to have a uniform composition of .
Low-frequency Raman and far-infrared spectra of both solid phases of CH 3 CN and CD 3 CN at temperatures between 20 K and the melting point have been recorded. Assignment of the observed peaks as librations about the ...
Low-frequency Raman and far-infrared spectra of both solid phases of CH 3 CN and CD 3 CN at temperatures between 20 K and the melting point have been recorded. Assignment of the observed peaks as librations about the principal molecular axes or as translational modes is facilitated by finding the frequency ratios of corresponding peaks for CH 3 CN and CD 3 CN. The spectra are compared with group theoretical predictions, based on possible space groups for each of the two phases. It is found that a unit cell with point group C 2 h and four molecules on general sites is favoured for phase I. The lattice spectra do not appear to be compatible with the larger unit cell proposed for phase II.
AbstractSelected portions of theS0andT1potential energy surfaces of acetaldehyde surveyed in our earlier studies have been reexamined. The assumption of the additivity of basis‐set polarization and of electron correl...
AbstractSelected portions of theS0andT1potential energy surfaces of acetaldehyde surveyed in our earlier studies have been reexamined. The assumption of the additivity of basis‐set polarization and of electron correlation effects used extensively in our earlier work on acetaldehyde has been tested through explicit polarized basis‐set electron‐correlation calculations. The “additivity assumption” introduces average absolute errors in energy differences of only 1.9 (MP3) to 3.4 (MP2) kcal mol−1in seven comparisons. The effects of using 6‒31G**SCFoptimized geometries as opposed to single‐point calculations on 3‒21G SCF structures (6–31G**//3–21G) as in our previous papers were examined. In six comparisons, the average absolute error in relative SCF energies introduced by the use of the 3–21G geometries rather than the fully consistent 6–31G–ones was only 0.3 kcal mole−1. After a uniform scaling procedure, comparisons of the 6–31G**and 3–21G calculated vibrational frequencies with experiment for CH3CHO (S0), CH4, and CO (20 comparisons) yielded absolute differences of 41 cm−1(6–31G**) and 57 cm−1(3–21G). All these more elaborate calculations support for the specific case of acetaldehyde and various minima and transition states of relevance to its photochemistry, the commonly used and practically important approximations (e.g.
Some ideas as to what the important factors are that will produce a reliable indium O‐ring seal are discussed. Four novel indium seal designs which are based on these ideas are presented. Three of these seals have be...
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Some ideas as to what the important factors are that will produce a reliable indium O‐ring seal are discussed. Four novel indium seal designs which are based on these ideas are presented. Three of these seals have been incorporated in a Brillouin cell. They include a simple sapphire window seal, a filling line union, and a flange seal. All of them have withstood low temperatures down to 77 K and moderate pressures up to 177 bar. The fourth seal described is a Pyrex tube seal for a Raman cell.
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