On the correlation between deuteron quadrupole coupling constants,O-H and O-D stretching frequencies and hydrogen-bond distances in solid hydrates

Correlation curves are reported relating deuteron quadrupole coupling constants (e²qQ/h) to O-H and O-D stretching frequencies (v_OH and v_OD) for isotopically-dilute HDO molecules. Correlation curves are also given relating these quantities to hydrogen-bond distances.The best correlations are found to be between (e²qQ/h) and v_OH andv_OD whereas the correlations involving intermolecular geometries show considerably greater scatter.Complications caused by the effects of anharmonicity on the stretching vibrations and of vibrational averaging of the quadrupole coupling and geometrical parameters are discussed in light of the observed correlations. It is concluded that, although these effects are large, their magnitude is also strongly correlated with the stretching frequencies, quadrupole couplings and geometrical parameters.     

The negative ion mass spectra of methanol and deuterated methanol

The negative ion mass spectra of methanol, methanol-d and trideuteromethanol have been measured at 70 eV. Use of deuterated methanols has enabled the ion at m/e 31 to be identified as CH₃O^? and not CH₂OH^?. Isotope effects have been determined for H^? and D^? formation, and for OH^? and OD^? formation. It has been shown that OH^? formation occurs as a rearrangement reaction as well as by simple C? O bond fission.     

Millimeter-wave rotational transitions and molecular constants of the diatomic silver iodide

In the 280 GHz region four rotational transitions of both isotopic species of AgI in vibrational states up to v = 2 have been measured. The analysis including frequencies of former observations in the 10 GHz region resulted in improved and new Dunham parameters Y_kl. From these data values of the vibrational constants ω_e and ω_ex_e have been deduced.     

Note on a theoretical interpretation of the isotopic ratio vOH/vOD versus vOH in isotopically diluted HDO molecules in solid hydrates

A simple intra- and inter-molecular potential for water molecules engaged in hydrogen bonding has been used in a one-dimensional approximation for a theoretical interpretation of the experimental correlation $\text{v}$_OH/$\text{v}$_OD versus $\text{v}$_OH in solid hydrates. The variation in the equilibrium OH(D) distance has also been considered.     

Radiation chemistry of xylenol orange in aqueous solutions at different acidities

The radiolytic decolourization and peroxide formation have been studied in aqueous solutions of xylenol orange (XO) at different acidities. The G(-XO) increases from 0.78 at pH 11, to 3.70 at pH 3. The peroxide yield also increases from 1.19 at pH 11, to 3.34 in 0.025 mol dm^-3 H₂SO₄. In alkaline solutions only the OH^. decolourizes XO whereas in acidic solutions both the H and OH^. decolourize XO though G(-XO) due to H-atoms is less. The ionization of the phenolic group in XO influences the e^-_aq reaction with it. In alkaline solution, the oxidized and reduced XO formed by OH^. and e^-_aq reactions, respectively, react together regenerating original XO. Near 0.025 mol dm^-3 H₂SO₄, there is an abstraction of H-atom from XO by HO₂ whereas at other acidities, H₂O₂ is formed by disproportionation of peroxides. Reaction schemes have been given to explain the various radiolytic yields.     

Hydrogen bonds in solid hydroxides, a bond valence approach

The bond valences s_OH due to the O-H bonds of OH⁻ ions in solids have been calculated indirectly from intermolecular H?O distances, viz. those within the Wigner Seitz cell around the respective hydrogen atom, by using the equation s_OH=1−∑s_H?O. The bond valences thus derived are an excellent measure of the strength of O-H bonds [J. Mol. Struct. 351 (1995) 205]. This is shown by their almost linear correlation with the wave numbers of the stretching modes of matrix isolated OD⁻ ions observed with IR or Raman experiments. In the case of very weak or lacking hydrogen bonds, this correlation fails because then other interionic bonding phenomena than hydrogen bonds as metal-oxygen interactions and hydrogen-hydrogen repulsion etc. gain in importance or dominate finally and, hence, partly or fully determine the wave numbers of the OD stretching modes, which, however, still remain a measure of the respective bond strengths. The relation of the distances r_OH, the bond valences s_OH, and the stretching modes ν_OD of both free, gaseous OH⁻ ions and H₂O molecules and those embedded in crystalline matrices is discussed.     

An infrared study of the stretching modes of the water molecules in ZnF2·4H2O

The IR spectra of ZnF₂·4H₂O and its deuterated analogues are reported at ambient and liquid-nitrogen temperatures. The OH and OD stretching and bending vibrations of the water molecules are analysed in detail. The two types of water molecules give rise to different absorption peaks in the OH and OD stretching regions in samples that contain isotopically dilute HDO groups. The strongly hydrogen-bonded water molecules H₂O(1) and H₂O(4) show four broad OH and OD stretching modes at lower frequencies, while the weaker hydrogen-bonded ones H₂O(2) and H₂O(3) give rise to four narrow bands at higher frequencies. The ν_OD frequencies of isotopically dilute HDO groups correlate very well with the known R(H---F) and R(H---O) distances in the crystals and the assignment of these modes was done on this basis. It was also found that the ratio ν_OH/ν_OD decreases with decreasing values of R(H---O) or R(H---F) in ZnF₂·4H₂O.     

The far infrared spectra of metal chloride complexes of pyridine in relation to their structures

The infrared spectra of the complexes [M(py)₂Cl₂] (py = pyridine; M = Mn, Fe, Co, Ni, Cu, Zn) have been determined within the range 650–150 cm^?1. Assignments of the metal—nitrogen and metal—halogen stretching frequencies (vM—N and vM—Cl) are made on the basis of the band shifts induced by deuteration of the pyridine ring and by varying the coordinated metal ion. If the band of lowest frequency is assigned to a bending mode, the number of vM—N and vM—Cl bands observed agrees with the number required by symmetry considerations based on the known structures of the complexes. On the basis of this work, some earlier assignments have been revised.     

CEPA calculations on open-shell molecules

Ab initio calculations at SCF and CEPA levels using large Gaussian basis sets have been performed for the two lowest electronic states,X ² Σ⁺ andA ² Π, of HeAr⁺. Spin-orbit coupling (SOC) effects have been added using a semiempirical treatment. The resulting potential curves for the three statesX,A ₁, andA ₂ have been used to evaluate molecular constants such as vibrational intervals ΔG(v + 1/2) and rotational constantsB _v as well as — by means of a Dunham expansion — equilibrium constants such asR _e , ω _e ,B _e etc. Comparison with the experimental data from UV emission spectroscopy shows that the calculated potential curves are slightly too shallow and have too large equilibrium distances:D _e = 242 cm^?1 andR _e = 2.66 Å compared to the experimental values of 262 cm^?1 and 2.585 Å, respectively, for theX ²Σ⁺ ground state. However, the ab initio calculations yield more bound vibrational levels than observed experimentally and allow for a more complete Dunham analysis, in particular for theA ₂ state. The experimental value of 154 cm^?1 for the dissociation energyD _e of this state is certainly too low; our best estimate is 180±5 cm^?1. For theA ₁ state our calculations are predictions since this state has not yet been observed experimentally.     

Nature of the broadening,the form of the spectral bands,and thev AH − RA...B correlation in liquids with hydrogen bonds

Conclusion The experimentally established correlation for crystals between the frequency of the OH (or OD) stretching vibrations and the interatomic separation R_O·O can also be used for each hydrogen bond in the liquid phase taken in isolation, if the equilibrium length R_e is used for R_O·O. The empirical correlation between the low-frequency shift of the band and its broadening results from the exponentialv _OH(R_e) relationship, while the distribution function of the frequencies in the vibrational spectrum P() corresponds to the distribution of the energies of the hydrogen bonds P(E). When the deflection of the equilibrium configurations of the H bonds can be neglected, P() is expressed unambiguously through the distribution of the lengths of the hydrogen bonds P(R_e) and makes it possible to determine their variance. Otherwise (the continuous network of strongly deflected H bonds in liquid water) the complex form of the spectral band and its temperature dependence can be described quantitatively by a simple equation of the Boltzmann type, in which the exponential part is the energy of the hydrogen bond (the depth of the potential well) making a contribution to the spectrum at the investigated frequency. The agreement between calculation and experiment reveals an important fact, i.e., the equality of the energies for the various configurations of the hydrogen bond producing one and the same frequencyv _OH.Institute of Chemical Kinetics and Combustion, Siberian Branch, Russian Academy of Sciences. Translated from Zhurnal Strukturnoi Khimii, Vol. 32, No. 6, pp. 72–80, November–December, 1991.     

Effect of the resonance of molecular vibrations on the ir spectra of hydrogen bonds

The effects are considered of the vibrations occurring with the group of atoms peripheral towards the hydrogen bond on the IR spectrum of the model hydrogen bond. It. is shown that the resonance of the v_OHv_CH stretching vibrations in a hydrogen bonded molecule result in the division of the v_OH band into two other bands having different polarizations. The resonance interaction leads to redistribution of the intensity and perturbs the regular Franck—Condon type envelope of the spectrum.     

Vapor phase infrared spectrum and coriolis coupling constants of pentacarbonyl(thiocarbonyl)chromium(0)

Several band contours have been successfully resolved in the high-resolution IR spectrum of pentacarbonyl(thiocarbonyl)chromium(0) vapor at ~312 K. However, PQR separations are only clearly discernible for the three v(CO) fundamentals (v₁,v₂ and v₁₆). The good agreement between the observed and calculated PR separations of the two a₁v(CO) modes (v₁ and v₂) verifies the C_4v prolate symmetrical top geometry of the molecule. From band shape analyses, the Coriolis coupling constants of the ev(CO) mode (v₁₆) and the e δ (CrCO) mode (v₁₇) are estimated to be —0.45 ± 0.05 and —0.80 ± 0.15, respectively.     

Synthesis,crystal structure and infrared spectroscopy of a novel copper strontium formate: CuSr(HCOO)4(H2O)2

The title compound CuSr(HCOO)₄(H₂O)₂ (1) forms a 3D polymeric structure, which basic structural units are SrO₉ polyhedra in the form of monocapped square antiprisms and distorted CuO₆ octahedra. The former groups organize as strips running parallel to the unique b axis, while interconnected by the latter into a strongly linked 3D covalent network.The infrared spectra of (1) confirm the existence of four nonequivalent formate groups with large deviations from C_2v molecular symmetry. The frequencies of the OD modes (isotopically dilute samples) are assigned on the basis of the respective intermolecular O_w⋯O bond lengths, the metal−water interactions (synergetic effect) and the different hydrogen bond acceptor capability of the oxygen atoms. The hydrogen bond acceptor strengths of the formate oxygen atoms are discussed within the framework of the Brown’s bond–valence theory. Intramolecular OH distances are derived from the novel ν_OD versus r_OH correlation curves [J. Mol. Struct. 351 (1995) 205; J. Mol. Struct. 404 (1997) 63)]. The librations of the water molecules are also discussed.     

Anomalous temperature dependence of the OH− absorption band in stoichiometric LiNbO3 crystals

Infrared absorption spectra of the stretching vibration of OH⁻ and OD⁻ ions in stoichiometric LiNbO₃ crystal have been measured in the temperature range 10–310 K. The band parameters, halfwidth and position, have been determined with high accuracy by assuming quasi-Voigt line shapes. Anomalous behaviour of the OH⁻ band position has been observed and interpreted by phonons coupled to the stretching vibration with coupling constants of alternate signs.     

Fluorescence spectrum of the benzene radical cation in solid argon

Argon/benzene samples were condensed at 12 K with continuous argon resonance radiation. Laser excitation at 421 nm produced a weak emission with structure at 19770, 19140 and 18290 cm^?1, assigned to the ²A_2u → ²E_1g emission of C₆H₆⁺. Observation of 630 and 1480 cm^?1 intervals for the vibrations v₁₈ (e_2g) and v₆ (e_2g), respectively, supports this assignment.     

Effet sterique sur les vitesses de transfert protonique: cyclohexanols substitues dans le dimethylsulfoxyde

Steric effects on proton transfer from, and to, hydroxylic oxygen have been studied in a series of seventeen α-methyl and a-benzyl cyclohexanols in anhydrous DMSO, under both acid and base catalysed conditions, using dynamic MNR techniques. The protonation rate constants (k₁ ? 10⁶ M^-1 s^-1 at 25°C) obey a Taft-Ingold relationship, containing only a steric contribution E_s = E_s^OH + E_s^α, where: E_s^OH = 0 or 0.15 for an axial or equatorial hydroxyl respectively and E_s^α = ?0.070 (or ?0.115) for substituting an α-hydrogen by a methyl (or benzyl) group. An equatorial hydroxylic function is therefore 40% more reactive than its axial homologue. These kinetic data are fairly consistent with structural information resulting from IR spectroscopy (v_co and v_OH vibrations) and from NMR (hydroxylic chemical shifts and coupling constants).     

Molecular structures,vibrational assignments and barriers to pseudorotation of gaseous niobium pentachloride and tantalum pentachloride from electron diffraction data

The pentachlorides of niobium and tantalum have trigonal bipyramidal structures (D_3hsymmetry) with thermal average axial bonds, r_α, longer than the equatorial ones by 0.097(9) and 0.142(5) Å, respectively. The equatorial bonds are r(Nb—Cl) = 2.241(4) and r(Ta—Cl) = 2.227(3) Å. Standard deviations are given. Calculated amplitudes of vibration for the e' type of bending frequencies assigned as v₆ (equatorial in-plane bend) < v₇ (axial—equatorial bend) agree significantly better with the experimental vibrational amplitudes than do amplitudes computed for the opposite assignment. Assuming an analytical quartic-harmonic potential for the pseudorotational motion of the molecules, barriers to pseudorotation of 1.5(0.7) and 1.2(0.6) kcal mol^?1 are estimated from the electron diffraction data for NbCl₅ and TaCl₅, respectively. Effects from interatomic multiple scattering are included in the theoretical intensities, and are found to be of some importance to the results.     

Model calculations of the vibrations of bonded water molecules

Model calculations have been made of the vibrational frequencies and normal modes of a water molecule vibrating in a combined internal and external field. A constant internal force field has been used together with an external central force field from four or three nearest-neighbour atoms to the water molecule. These neighbour atoms have been arranged either tetrahedrally or trigonally around the water molecule. The external force field has been further restricted by the use of five possible site symmetries for the water molecule, C_2v, C₂, C_s(σ_xz, C_s(σ_yz) and C₁. A series of calculations have been made where the external force constants have been varied within the range 1—80 Nm^?1.The nine calculated normal modes can be divided into three groups: intra-molecular, rotational and translational vibrations. Among the rotational vibrations it is found that, in the tetrahedral environment, the rocking mode occurs at lower frequencies than the twisting and wagging modes, whereas the opposite occurs for the trigonal environment. Frequency ratios have been calculated using the isotopic species H₂O, D₂O, HDO and H,¹⁸O. The twisting and wagging modes have the vH₂O/vD₂O ratio in the range 1.35-3-1.41 and the rocking mode in the range 1.26—1.41.     

Velocity modulation laser spectroscopy of vibrationally excited CF+ determination of the molecular potential function

The lowest six vibrational hot bands of CF⁺ have been measured in a helium/C₂F₆ discharge by velocity modulation laser spectroscopy. A total of 56 transitions has been fitted to Dunham expansion for v = 0–7, yielding the parameters: ω_e = 1792.6654(18) cm⁻¹B_e = 1.7204176(75) cm⁻¹, Y₂₀, = −13.22968(54) cm⁻¹, and D₀ = 62086(30) cm⁻¹. The rotational temperature of CF⁺ in the plasma is near 650 K and the vibrational temperature is approximately 5200 K.     

Hydrogen bond studies : 79. Correlation curves for properties of hydrogen bonded water molecules based on ab initio calculations

Correlation curves have been derived from previous ab initio MO-LCAO-SCF calculations made on water molecules in hydrates. The OH-stretching frequency shifts have been correlated with: (a) ratios of the intensity of v?v_OH for bonded water to that for free water, (b) shifts in the OH-distances and (c) quadrupole coupling constants for deuterium in D₂O. Shifts in quadrupole coupling constants are also correlated with shifts in OH-distances. Comparisons have been made with experimental data and the agreement is found to be satisfactory.