Anharmonic interatomic potentials of octahedral Pt-halogen complexes studied by extended x-ray-absorption fine structure

Abstract

The temperature dependence of Pt L III -and I K-edge extended x-ray-absorption fine-structure spectra of octahedrally coordinated Pt X 6 2Ϫ (XϭCl, Br, and I͒ complexes has experimentally been investigated not only for the first-nearest-neighbor ͑NN͒ shells but for higher NN ones. The second-and third-order cumulants of a radial distribution function in the octahedral system have been evaluated quantum mechanically by employing the interatomic potential including the third-order force constants. The experimentally obtained second-order cumulants agree with the values expected by the vibrational data and the third-order cumulants have successfully given the anharmonic force constants. Contribution of the bending motions to the cumulants of higher NN shells is discussed in detail.

Accurate determination of molecular structures by x-ray absorption spectroscopy

“…[11][12][13] The effect of the nonharmonic corrections to the interatomic potential for simple molecules has been thoroughly investigated by Yokoyama and co-workers for diatomic, linear triatomic, tetrahedral, and octahedral molecules. [14][15][16] The typical bond-length error quoted for the standard XAFS data-analysis procedure is about 0.01 Å, which is clearly not sufficient for very accurate determinations of molecular structures. Recent developments in the XAS experimental facilities and in the theoretical framework for data interpretation have considerably improved the reliability of XAFS investigations.…”

Thermal expansion and anharmonicity of solid Kr studied by extended x-ray-absorption fine structure

“…Since the interatomic potential is generally asymmetric with respect to the potential minimum, the average interatomic distance is temperature dependent and usually increases with a temperature rise because of a looser barrier at a longer distance side. Extended x-ray-absorption fine-structure ͑EXAFS͒ spectroscopy gives information on local thermal expansion and anharmonicity for solids, 1-4 molecules, [5][6][7] and noncrystalline materials 2 owing to the establishment of the cumulant-expansion technique. 8 Very recently, the relationship between the EXAFS cumulants and the anharmonic interatomic potential has also been clarified, 3,[5][6][7][9][10][11] including many-atom systems 5-7,10,11 and many-body forces.…”

“…Extended x-ray-absorption fine-structure ͑EXAFS͒ spectroscopy gives information on local thermal expansion and anharmonicity for solids, 1-4 molecules, [5][6][7] and noncrystalline materials 2 owing to the establishment of the cumulant-expansion technique. 8 Very recently, the relationship between the EXAFS cumulants and the anharmonic interatomic potential has also been clarified, 3,[5][6][7][9][10][11] including many-atom systems 5-7,10,11 and many-body forces. 6,7 Since thermal expansion originates from anharmonicity of a pair potential, it happens to be believed that, when the asymmetric distribution is neglected in the EXAFS analysis by assuming the Gaussian distribution function, thermal expansion cannot be estimated and the obtained distance is erroneously getting shorter with a temperature rise.…”

Observation of anharmonicity for copper thin film near room temperatures

“…The anharmonicity of atomic vibration has been frequently reported in the extended absorption fine structure (EXAFS) fields since Tranquada pointed out that CuBr has the anharmonicity at a very low temperature (Yokoyama, et al, 1996, Sayers, et al, 1971, Stern et al, 1975, Tranquada & Ingalls, 1983. Recently, studies of anharmonicity have been stimulated to measure the thermal expansion of atoms in solids (Frenkel & Rehr, 1993, Dalba et al, 1993, Tröger et al, 1994, Yang & Joo, 1998.…”