Isotopic Frequency Shifts Research Articles

A calculation of the isotope frequency shifts of local mode caused by interstitial oxygen in single crystal silicon

In the present paper, a calculation of the isotope frequency shifts of local mode caused by interstitial oxygen in silicon is presented by using a 9-atom cluster model based on the force constant approach. We find that the calculated result is not better than that of a single Si 2O molecular model. Even if the effects of non-central force and local distortion of lattice are taken into account, the result is still not expected well. In order to obtain the best fit with the experimental isotopic shifts, it is necessary to introduce the variation of the Si-O force constant with the different isotopes. It turns out that the Si-O force constant increases with increasing the mass of silicon atom but decreases with increasing the mass of oxygen atom.

Structure of Borate Groups in Boron-Containing Apatite

11B- and 10B-containing apatites were prepared from the system CaO-P2O5-B2O3 at 1000°C. The structure of borate groups was investigated by infrared spectroscopy based on isotopic frequency shifts. The boron-containing apatite has both BO2 and BO3 groups, but it does not contain BO4 groups. The BO3 groups occupy PO4 site of the apatite structure.

Vibrational spectra and normal coordinate analysis of p-cresol and its deuterated analogs

I.r. and Raman spectra of p-cresol and its seven deuterated analogs were investigated in dilute solutions of hydrophobic solvents. Assignments of the observed i.r. and Raman bands were made on the basis of isotopic frequency shifts, Raman polarization properties, i.r. intensifies and normal coordinate calculations. The calculated normal frequencies are in good agreement with the experimental ones: the average error below 1700 cm −1 is 3.8 cm −1 for 164 in-plane vibrations and 3.3 cm −1 for 59 out-of-plane vibrations. The calculated vibrational modes may be useful in analysing the vibrational spectra of tyrosine. It is suggested that several doublets due to Fermi resonance and a trio of Raman bands in the 1260-1160 cm −1 region are potential probes for the micro-environments of tyrosine side chains in proteins.

Theory of impurity vibrations due to isolated interstitials and interstitial-substitutional pair defects in semiconductors.

Dynamical properties of isolated interstitials and ``interstitial substitutional'' pair defects in semiconductors are reported with use of the well-known Green's-function technique. To make the problem amenable to calculations, we exploit the symmetry properties of the defect environment and assume the interstitial site to be tetrahedral. For the isolated-impurity case, the perturbation is restricted to the impurity interacting with the host lattice atoms up to and including second-nearest neighbors. Similar to the substitutional-impurity vibrations, the contribution of the nearest-neighbor interactions to the dynamical properties of interstitials in semiconductors is found to be appreciable. For light defects (e.g., ${\mathrm{Li}}_{\mathrm{int}}$ in Si and CdTe), a single dimensionless nearest-neighbor perturbation parameter \ensuremath{\tau} has provided the isotopic frequency shifts of localized vibrational modes, in excellent agreement with the observed optical data. To explain the observed isotopic shifts of inband resonance modes due to heavier impurities (e.g., $^{63}\mathrm{Cu}$, $^{65}\mathrm{Cu}$ in Si, etc.) the effect of second-nearest-neighbor impurity-host interaction is found to be important. Finally, the calculated force-constant changes due to isolated substitutional and interstitial impurities are used to understand the ``interstitial-substitutional'' pair defect vibrations in Si and CdTe.

Structural and spectral consequences of ion pairing II. a theoretical study of CIO −3Li + and ClO −3Na +

The structure of ClO − 3M + ion pairs (M = Li, Na) has been examined with the aid of ab initio molecular orbital calculations. The calculations support recent experimental findings that ClO − 3 M ion paris have C 3v rather than C s configurations. Results from these studies also show that the metal cation prefers to coordinate at the base of the chlorate anion pyramidal structure along the C 3 axis. Calculated vibrational frequencies, intensities, isotopic frequency shifts, and isotopic substituted frequency and intensity patterns render support to this conclusion. New vibrational assignments of observed and some unassignable bands from previous matrix-isolation and molten gas phase spectroscopic studies of ClO − 3M + ion pairs are provided.

An infrared and Raman study of the isotopic species of .alpha.-quartz

The authors have obtained Raman and infrared spectra for the 28/30 Si and 16/18 O isotopic species of ..cap alpha..-quartz. The isotopic frequency shifts give valuable information on atomic participation in individual vibrational modes. Comparisons of their isotopic shifts with displacement patterns predicted from a number of dynamical calculations have been made. Most calculated modes agree well with the observed isotope shifts, but some do not. For example, the strong Raman line at 464 cm/sup -1/ shows no silicon displacement but a large oxygen shift, consistent with its usual assignment to a motion of the bridging oxygens in the plane bisecting the SiOSi linkage. However, the soft mode at 206 cm/sup -1/, which is commonly accepted as being due to motion of Si and O around a 3-fold screw axis related to the ..cap alpha..-..beta.. displacive transition in quartz, shows no Si isotope shift and hence no silicon participation in this vibration.

High resolution measurement of the3 P 1?3 P 0 transition isotopic shift between24Mg and26Mg

The isotopic frequency shift for the3P1–3P0 ΔmJ=0 fine structure transition in the metastable triplet of24Mg and26Mg is reported. The transitions corresponding to the two even isotopes of Mg (λ≃498 µm) are observed in a metastable atomic beam through a two-zones Ramsey interaction technique with a transit time limited full width at half maximum of 1.2 kHz (Q=5×108). The isotopic shift turned out to be 1712.5±0.2 kHz.

The empirical general harmonic force field of methylene chloride

The general harmonic force field of methylene chloride has been calculated without the necessity of imposing constraints, through the use of a set of 74 observables over eight isotopic species. These include vibration frequencies, 37Cl and 13C isotopic frequency shifts, and quartic centrifugal distortion constants. All force constants are well defined by the data with one exception, and this takes a value close to that predicted by transfer from methyl chloride, although with an uncertainty larger than itself. The force field is used to predict precise isotopic distortion constants, in terms of differences from the accurate experimental values for CH 2 35Cl 2 and CD 2 35Cl 2, and to calculate Coriolis interaction constants which will be of assistance in high-resolution rovibration studies. Alternative definitions which may be used for the deformation coordinates of an XY 2Z 2 molecule are considered. That which associates each deformation uniquely with either the XY 2 or XZ 2 group is clearly preferred.

Vibrational spectra of trimethyl gallium species in relation to the force field and methyl group internal rotation

Infrared and Raman spectra are reported for Ga(CH 3) 3, Ga(CD 3) 3 and Ga(CHD 2) 3 in the gas phase. These were also examined in the i.r. spectrum in the solid phase at 78 K. The new Raman spectra of the CHD 2 species strongly support earlier i.r. evidence for CH force constant variation during free internal rotation of the methyl groups, from the presence of two bands at 2940 (vs) and 2922 cm −1 (w) identified as due to ν av is and ν † is respectively. The observed a′ and e′ frequencies of the d 0 and d 9 species are used to obtain a force field in which three interaction constants are well defined. The best value of the Ga-C stretching force constant is 2.356(28) mdyn Å −1. In the crystal phase at 78 K, the e′ modes due to δ s Me and ν as GaC 3 are split, indicating a site group symmetry lower than C 3. Gallium and carbon isotope frequency shifts are predicted.

High resolution infrared analyses of fundamentals and overtones in isotopic ketenes

Rovibrational structure in the ν 5, ν 6, ν 7, ν 8 fundamentals and 2ν 5, 2ν 6 overtones in each of H 2 12C 12CO, H 2 12C 13CO, H 2 13C 12CO has been assigned and analysed. The effects of Fermi resonance between ν 7 and ν 2+ν 8 are corrected for, and a set of accurate unperturbed vibrational frequencies and 13C isotopic frequency shifts therefrom is obtained. The changing effects of the major Coriolis interactions involving the out-of-plane fundamentals, ν 5 and ν 6, are manifest in varying isotopic displacements of equivalent Q branch structures between the isotopic species studied, from which accurate isotopic vibrational shifts are obtained. Variable anharmonicity constants associated with the vibration frequencies of 2ν 5 and 2ν 6 give evidence of major Fermi resonance interactions between both overtones and the ν 4 fundamental, which they straddle.

Les composes de coordination des halogenures d'aluminium: mise au point sur leurs proprietes structurales et les methodes d'analyses

Les composes de coordination des halogenures d'aluminium: mise au point sur leurs proprietes structurales et les methodes d'analyses

The configuration of transition metal coordination compounds containing the anion of hexahydro-1,3,5-triazine-1,3,5-triol

The configuration of Ni(IV), Fe(IV), Mn(IV) and V(IV) complexes of the type M I 2[M IVL 2] where M I=Li, Na, K, Rb and Cs and the ligand L is the anion C 3H 6N 3O 3− 3 of hexahydro-1,3,5-triazine-1,3,5-triol has been obtained by studying the infrared spectra of the complexes in the region 4000-50 cm −1. Vibrational assignments for the observed bands of the complex ions have been made assuming the molecular symmetry D 3 d . The assignments have been based on the observed isotopic frequency shifts due to the substitutions H/D, 14N/ 15N, 12C/ 13C, 58Ni/ 62Ni and 54Fe/ 57Fe and on the assignment of the bands in the infrared spectrum of hexahydro-1,3,5-triazine-1,3,5-triol, C 3H 6N 3 (OH) 3.

Vibrational spectra, normal coordinates and infrared intensities of four isotopic phenyl acetates

The i.r. and Raman spectra of phenyl acetate and its deuteromethyl and deuterophenyl derivatives have been recorded. The fundamental frequencies of the four isotopic species have been assigned by referring to the Raman depolarization ratios and isotopic frequency shifts. The normal coordinates have been calculated on the basis of a valence force field. The general valence type force constants have been refined by the least-squares method. The i.r. spectra of the four isotopes have been simulated by using the obtained force field in combination with a suitable set of the atomic charges and their fluxes.

Vibrational levels and anharmonicity in SF 6—I. Vibrational band analysis

The vibrational spectrum of SF 6 has been recorded with a Fourier-transform i.r. spectrometer at a resolution of 0.05 cm −1 and pressure—path length products of up to 2 × 10 5 Torr-cm. Twenty-nine bands were observed. Rotational structure was resolved for 11 of these and polynomials were fitted to the observed frequencies to yield the scalar spectroscopic constants, including the band origins m and derived values of B′ B 0 and the Coriolis constants ζ. For 12 other unresolved bands accurate estimates of the origins could be made from the frequency of a sharp Q-branch edge. Three more bands (ν 3, 2ν 1 + ν 3, and 3ν 3) were not resolvable at our resolution but have been previously analyzed from Doppler-limited or sub-Doppler spectra. In addition, about 10 assignable hot bands were observed whose frequency shifts relative to the principal transitions could be accurately measured; two of these were sufficiently resolved for full scalar analyses. These frequencies were combined with results of several high-resolution Raman studies by other authors to yield the most complete data set on SF 6 vibrational levels yet obtained. Isotopic frequency shifts have also been measured. The effective Coriolis constants for combination and overtone bands of octahedral molecules are discussed.

Vibrational isotope shifts in hexafluoride molecules

Central-atom isotope frequency shifts for the v 3 stretching fundamentals of octahedral hexafluorides are reviewed. Accurate shifts have been measured for the hexafluorides of S, Se, Mo, Te, W and U, and can be calculated from force fields for those of Rh, Ir, Pt, Np and Pu. A theoretical treatment of the relation between the vibrational frequency v 3 and the central-atom mass m establishes the parametric dependence of the isotope shift Δ v 3. This yields a semi-empirical formula Δ v 3(cm −1amu −1) = −4.20 v 3 m −1.75, with v 3 in cm −1 and m in amu. Frequency shifts calculated from this formula agree with measured shifts generally to within 5%, and it promises to be useful in estimating such shifts for Jahn—Teller hexafluorides and for hexafluoride ions. The relative precision of isotope frequency shifts and Coriolis constants in constraining the general quadratic force fields of XF 6 molecules has also been considered. For a given precision in measuring frequency shifts, Δ v 3 is more effective than Δ v 4, by the ratio v 3/ v 4, for determining the off-diagonal symmetry force constant F 34. F 34 is about equally well constrained by the Coriolis constants for all molecules, but the frequency shifts become much less effective for this purpose as the central-atom mass increases.

Lnfrared spectra and molecular association of lumiflavin and riboflavin derivatives

Infrared spectra of lumiflavin (Lf), [3-ND]Lf, [3-NMe]Lf, [2- 13C]Lf, [4a- 13C]Lf, [1,3- 15N]Lf, [1,3,5- 15N]Lf, riboflavin (Rf), [3-NMe]Rf, riboflavin-2′,3′,4′,5′-tetraacetate (RfT) and [3-NMe]RfT were measured in their solid and solution states. The vibrational assignments of lumiflavin have been made on the basis of the observed isotope frequency shifts in the i.r. spectra. The differences between the skeletal vibrations of Lf and those of Rf are discussed. The modes of molecular association of Lf and Rf are also proposed based on the i.r. spectra of the carbonyl stretching region.

Vibrational levels and anharmonicity in SF 6—II. Anharmonic and potential constants

Expressions for the vibrational energy levels of spherical-top molecules are reviewed. We show that even without a full analysis of the anharmonic splitting of higher vibrational states, the positions of many observed transitions can be adequately described with “effective” anharmonicity constants that combine some of the (unknown) splitting terms together with the “true” anharmonicity constants X ij . A notation is developed that distinguishes between the effective constants obtained from binary ( X′ ij ) and various types of ternary ( X′' ij , …) combinations. On this basis we analyze the data set of the previous paper on the vibrational levels of SF 6, based largely on FTIR spectra obtained at a resolution of 0.05 cm −1. Many of the anharmonicity constants determine the frequencies of several bands, and can be fitted to the data by least-squares regression with standard deviations of 0.001-0.05 cm −1. Of the 21 constants X ij , we obtain values for six, plus 12 X′ ij s obtained from binary combinations and one ( X‴ 22) from ternary combinations. Of the two constants undetermined in this paper, a precise value of X 33 is available from high-resolution spectroscopy of 3ν 3, and only X 35 remains unknown. The fit also yields band origins for the i.r.-inactive bending fundamentals ν 5 and ν 6. Using these constants, we estimate the harmonic fundamental frequencies ω i . The general quadratic force field of SF 6 has been redetermined, using as constraints in the F 1 u block the central-atom isotopic frequency shifts and the Coriolis constants ζ 3 and ζ 4.

Molecular Vibrations of Gallium Trichloride Monomer with Application of the Keating Bending

The vibrational spectra and previous normal coordinate analyses of GaCl3 are reviewed. The valence force field (VFF), Keating force field (KFF) and central force field (CFF) are investigated, taking into account isotopic frequency shifts and the mass influence on Coriolis constants. It seems that KFF is an appropriate force field approximation. In its definition a new type of internal coordinates, the Keating's bending, is invoked. A final force Field is tentatively determined and used to calculate the mean amplitudes of vibration.

Anomalous isotope effect for hindered rotations: H2O adsorbed on metal surfaces.

The frequency shift of the hindered rotation of a deuterated ${\mathrm{H}}_{2}$O molecule adsorbed on a metal surface departs substantially from that given by the classical Teller-Redlich rule. Because of the large zero-point motion of the molecule a quantum-mechanical treatment is necessary to relate the isotope frequency shift with the change in the mass. The ratio of the corresponding electron-energy-loss line intensities provides an important additional check of the mode assignment.

Ca(C 5H 3O 3N 4) 2 · 6H 2O: A new hydrate of calcium urate

Calcium urate hexahydrate, Ca(C 5H 3O 3N 4) 2 · 6H 2O, has been synthesized for the first time. A tentative assignment of some infrared and Raman bands is given by referring to the isotopic frequency shifts, group frequency considerations, Raman intensities as well as to the spectrum of potassium salt. The spectroscopic data suggest that there are, at least, two types of water molecules in the unit cell. Centrosymmetric unit cell is proposed to explain the spectral features of this compound. X-Ray powder diffraction data are also given.