Internal mode (factor group) splitting in hydrogen halide crystals
28 Jul 1976-Journal of Physics C: Solid State Physics (IOP Publishing)-Vol. 9, Iss: 14, pp 2673-2679
TL;DR: A detailed theoretical study of the influence of relevant intermolecular interactions in the splitting of fundamental stretching (internal) modes in hydrogen halide crystals has been undertaken in this paper, where the molecular exciton theory of Davydov has been used.
Abstract: A detailed theoretical study is undertaken of the influence of the relevant intermolecular interactions in the splitting of fundamental stretching (internal) modes in hydrogen halide crystals. The molecular exciton theory of Davydov has been used. Lattice sums have been carried out till good convergence is obtained. It is observed that the exchange interaction can be neglected in these crystals. The induction forces have a small contribution in the splitting, while the contribution from the dispersion forces is almost negligible. But the dipole-dipole interaction alone cannot account for the splitting of the internal mode and the quadrupole-quadrupole interaction must be taken into account. This is true since in these crystals the molecules possess a large value of the quadrupole moment and its first derivative with respect to the vibrational coordinate.
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TL;DR: Spectra of large clusters of about 500 molecules consist of a single band, which encompasses the same frequency range of trimers through hexamers, which correlates well with the onset of the folded cyclic structure and the full development of the hydrogen bonding in larger clusters.
Abstract: Presented here are the results of the joint theoretical and infrared laser spectroscopic study of the hydrogen chloride monomer and clusters, (HCl)n (n = 1−6), isolated in helium nanodroplets. The H−Cl stretching bands of the dimers and trimers show a large increase in the band intensity as well as low frequency shift with respect to that in a single HCl molecule. The average frequency of the bands for clusters larger than trimers remains approximately constant, which correlates well with the onset of the folded cyclic structure and the full development of the hydrogen bonding in larger clusters. The structure of the clusters was found to be cyclic planar for trimers, slightly twisted square planar for tetramers, envelope-like for pentamers, and folded pseudobipyramidal for hexamers. This change in structure upon an increase of the cluster size can be seen as an early stage of the structural transition to the HCl solid, which consists of zigzag chains of HCl molecules. Spectra of large clusters of about 5...
20 citations
TL;DR: In this paper, the contribution of long-range dipole-dipole forces to the energy of the internal modes in a series of molecular crystals has been evaluated using the Weald-Kornfeld summation method.
Abstract: The contribution of long-range dipole-dipole forces to the energy of the internal modes in a series of molecular crystals has been evaluated using the Weald-Kornfeld summation method. Comparison with experimental infrared observations such as LO-TO and Davydov splittings, gas to crystal frequency shifts, band shapes, transition dipole moments, phonon bandwidths, is discussed.
18 citations
TL;DR: In this paper, the effect of pressure on the vibration-orientation spectra of various hydracid polymers in rare gas matrices is discussed from an experimental and theoretical point of view.
Abstract: The modifications induced by pressure on the vibration–orientation spectra of the various hydracid polymers in rare gas matrices are discussed from an experimental and theoretical point of view. The main experimental results obtained are the blue shifts of the monomer and one of the dimer bands and the red shifts of all the other poylmeric bands under increasing pressure. The interpretation in terms of the intermolecular potential is based on a hydrostatic pressure model which contracts the lattice parameter and shortens the intermolecular distance between hydracids. When pressure increases, the angular geometries of the polymers determined at P = 0 are nearly unchanged although the overlap of the electronic clouds of two neighboring molecules becomes more and more important. On the contrary, the potential derivatives with respect to the internal vibrational coordinates are considerably amplified by a charge transfer process due to this overlap. The quasicontinuous study of this evolution with the pressure enables a quantitative discussion of this little known phenomenon in weakly hydrogen bonded species. A model of the molecular parameter derivatives modification due to this charge transfer is proposed and found in quantitative agreement with experiment.
10 citations
TL;DR: In this paper, the existence of layer and crystal symmetries is clearly manifested in the vibrational spectra of these crystals which have been determined in recent years by means of infrared and Raman investigations of the zone center modes.
Abstract: Layer crystals have received considerable attention of spectroscopists because of the wide range of electrical and optical properties they possess. The group of layered chalcogenide crystals contains insulators, semiconductors, metals, and superconductors at moderately high temperature. The layered halide crystals act as reliable hosts for Jahn-Teller, ESR, and other optical experiments. The layerlike nature of such crystals leads to experimentally distinguishable lattice optical properties. The existence of layer and crystal symmetries is clearly manifested in the vibrational spectra of these crystals which have been determined in recent years by means of infrared and Raman investigations of the zone center modes. The large anisotropy of electrical properties leads to LO-TO splitting, while the small interlayer interaction gives rise to Davydov-type splitting besides low frequency interlayer modes. Thus investigations of such crystals have been a considerable addition to our knowledge of the vib...
6 citations
01 Jan 1981
TL;DR: In this article, an electrostatic interaction potential has been used to explain the factor group splitting in several molecular crystals composed of small inorganic molecules, and the potential function is expanded in terms of molecular multipole moments.
Abstract: An electrostatic interaction potential has been used to explain the factor group splitting in several molecular crystals composed of small inorganic molecules. The potential function is expanded in terms of molecular multipole moments. It is shown that the dipolar coupling mechanism is not sufficient to reproduce the observed splitting in these crystals and that the quadrupolar interactions play a dominant role. In case of hydrogen halide and alkaline earth hydroxide crystals dipole-dipole, dipolequadrupole and quadrupole-quadrupole interactions can explain the splitting. The values of the quadrupole moment derivatives obtained from such studies are compared with those obtained from ab initio calculations. The possibility of obtaining quadrupole moment derivative from the observed factor group splitting will be discussed. The role of quadrupolar interaction in the case of cyanogen bromide crystal will also be examined.
1 citations
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TL;DR: In this paper, a review of available information on molecular quadrupole and higher moments is presented and a theorem is proved which shows that only one independent scalar quantity is required to determine a molecular electric multipole tensor of rank p for molecules with an n-fold axis of symmetry where p < n.
Abstract: A summary and critical review of available information on molecular quadrupole and higher moments is presented. A theorem is also proved which shows that only one independent scalar quantity is required to determine a molecular electric multipole tensor of rank p for molecules with an n-fold axis of symmetry where p < n.
733 citations
TL;DR: In this article, a one-dimensional model for hydrogen bonding is proposed based on the potential function V = D[1-exp(nΔr2/2r)] and the energy associated with both the weak and strong bonds of the configuration RO - H - - - OR2 is obtained through application of this function.
Abstract: A one‐dimensional model for hydrogen bonding is proposed based on the potential function V = D[1—exp(—nΔr2/2r)]. The energy associated with both the weak and strong bonds of the configuration RO – H – – – OR2 is obtained through application of this function. A repulsive Van der Waals potential and an attractive electrostatic potential are also assumed to exist between the two electronegative atoms of the hydrogen bond. Through application of the conditions describing a stable equilibrium, relations are obtained which permit a calculation of OH frequency shifts, OH bonded distances, hydrogen bond energies and ko — — — o force constants, all as a function of the O – – – O distance R. The calculated quantities agree well with those obtained from neutron diffraction, infrared, and other experimental studies. Because of the assumptions involved, this model is best used to describe the properties of hydrogen bonds in crystals. The model is also capable of extention to describe the properties of other types of h...
578 citations
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TL;DR: In this paper, it was shown that the double-well potentials acting on the protons are highly asymmetric, and the probability of proton transfer in the hydrogen bonds of DNA is further discussed.
Abstract: Publisher Summary This chapter discusses aspects on the biological problems of heredity, mutations, aging, and tumors in view of the quantum theory of the DNA molecule. Each hydrogen bond in DNA consists of a proton shared between two electron lone pairs, and the genetic code is essentially a proton code. The probability of proton transfer in the hydrogen bonds of DNA is further discussed. By using the available charge orders for the π electrons of the base pairs, it is shown that the double-well potentials acting on the protons are highly asymmetric. At normal temperature, there is practically no proton transfer above the barrier, explaining the enormous stability of the genetic code. According to quantum mechanics, however, a proton is not a classical particle but a “wave packet,” which may penetrate a potential barrier by means of the “tunnel effect.” Depending on this proton tunneling, there is hence a very small but with time increasing probability that the normal base pairs A-T and G-C may spontaneously go over into the tautomeric pairs A*-T* and G*-C* through a “proton exchange” along the hydrogen bonds. Since the tautomeric bases have another pairing pattern, the proton exchange leads inevitably to errors in the genetic base sequence in the next duplication. The various possibilities suggested for the transcription of the genetic code through the formation of messenger RNA are studied, and the present status of the coding problem in protein synthesis is briefly reviewed.
346 citations