Hydrogen Vibrations Research Articles

Synthesis and Specific Heat of CaPdH3-δwith the Perovskite Structure

Single-phase samples of the hydrogen-deficient perovskite hydride CaPdH 3-δ with δ= 0.9 have successfully been synthesized. First, a homogeneous alloy of CaPd was prepared through the hydrogenation and subsequent dehydrogenation of an inhomogeneous alloy of CaPd obtained through the induction melting of Ca and Pd metals. Next, CaPdH 3-δ with δ= 0.9 was synthesized through the hydrogenation of the homogeneous CaPd alloy at room temperature. No superconductivity has been observed above 2 K in the magnetic-susceptibility measurements. The specific-heat measurements have revealed that there exist optical phonons due to hydrogen vibrations with the Einstein temperature as high as about 1000 K.

SiGe superlattice nanocrystal infrared and Raman spectra: A density functional theory study

Infrared and Raman vibrational spectrum are calculated using ab initio density functional theory for SiGe superlattice nanocrystal of approximately 1.6 nm length. After obtaining the optimum positions of atoms via geometrical optimization using density functional theory, coupled perturbed Hartree-Fock equations are solved iteratively to obtain vibrational spectrum. Frequencies of vibrations are analyzed against intensities, reduced masses, and vibrational force constants. A scale factor of 0.81 is suggested to correct the frequencies of the present calculations that are obtained using STO-3 G basis functions. Results show that SiGe nanocrystals have complex and rich vibrational spectrum that can be generally divided into three regions. The highest reduced masses are in the first region where Si and Ge atoms are the main contributors to vibrations with a smaller number of vibrations attributed to hydrogen atoms. The highest intensity lines in SiGe superlattice nanocrystals are in the middle region where most of the modes of vibration can be excited. The third region is characterized by high force constants. The first region shows a redshift of the original Ge-Si bond vibration from the calculated bulk 418 cm−1 to the present nanocrystal 395 cm−1. Hydrogen vibrations interferences are found in the same redshift region that might induce uncertainties in the experimentally measured redshift. Si-H and Ge-H vibrations are observed mainly in the second and third region and less frequently in the first region. These vibrations include modes of vibration such as symmetric, asymmetric, wagging, scissor, rocking, and twisting modes.

The molecular structure of the multianion mineral hidalgoite PbAl3(AsO4)(SO4)(OH)6 – Implications for arsenic removal from soils

► We have researched the structure of the mineral hidalgoite. ► The relationship of this mineral to other related minerals of the beaudantite mineral group is discussed. ► Observed bands are assigned to the stretching and bending vibrations of (SO 4 ) 2− and (AsO 4 ) 3− units. ► The formation of hidalgoite may offer a mechanism for the removal of arsenic from the environment. The objective of this research is to determine the molecular structure of the mineral hidalgoite PbAl 3 (AsO 4 )(SO 4 )(OH) 6 using vibrational spectroscopy. The mineral is found in old mine sites. Observed bands are assigned to the stretching and bending vibrations of (SO 4 ) 2− and (AsO 4 ) 3− units, stretching and bending vibrations of hydrogen bonded (OH) − ions and Al 3+ –(O,OH) units. The approximate range of O–H⋯O hydrogen bond lengths is inferred from the Raman and infrared spectra. Values of 2.6989 Å, 2.7682 Å, 2.8659 Å were obtained. The formation of hidalgoite may offer a mechanism for the removal of arsenic from the environment.

The structure of the mineral leogangite Cu 10(OH) 6(SO 4)(AsO 4) 4·8H 2O—Implications for arsenic accumulation and removal

The objective of this research is to determine the molecular structure of the mineral leogangite. The formation of the types of arsenosulphate minerals offers a mechanism for arsenate removal from soils and mine dumps. Raman and infrared spectroscopy have been used to characterise the mineral. Observed bands are assigned to the stretching and bending vibrations of (SO 4) 2− and (AsO 4) 3− units, stretching and bending vibrations of hydrogen bonded (OH) − ions and Cu 2+-(O,OH) units. The approximate range of O–H⋯O hydrogen bond lengths is inferred from the Raman spectra. Raman spectra of leogangite from different origins differ in that some spectra are more complex, where bands are sharp and the degenerate bands of (SO 4) 2− and (AsO 4) 3− are split and more intense. Lower wavenumbers of δ H 2O bending vibration in the spectrum may indicate the presence of weaker hydrogen bonds compared with those in different leogangite samples. The formation of leogangite offers a mechanism for the removal of arsenic from the environment.

Theoretical study of the polarized infrared spectra of the hydrogen bond in 2-furoic acid crystal dimer

This work presents a theoretical simulation of νOH and νOD band shapes in the polarized infrared spectra of 2-furoic acid dimer crystals measured at liquid-nitrogen temperature. The line shapes are studied theoretically within the framework of the anharmonic couplings between low-frequency hydrogen-bond vibrations and degenerate excited states of high-frequency hydrogen vibrations in hydrogen-bonded dimers and the anharmonic coupling between the first excited state of the fast mode and the harmonics or band combinations of some low-frequency bending modes, which lead to Fermi resonances.This approach takes into account the adiabatic approximation, the intrinsic anharmonicity of the low-frequency mode through a Morse potential, Davydov coupling triggered by resonance exchange between the excited states of the fast modes of the two hydrogen bonds involved in the cyclic dimer, and the direct and indirect damping of the fast-stretching modes of the hydrogen bonds and of the bending modes. The infrared spectral density was calculated within the linear response theory by Fourier transform of the autocorrelation function of the transition dipole moment operator of the fast mode. Numerical results show that mixing of all these effects allows satisfactory reproduction of the main features of the experimental IR line shapes of crystalline H- and D-bonded 2-furoic acid at liquid-nitrogen temperature and for different polarizations. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012

The stretching vibration of hydrogen adsorbed on epitaxial graphene studied by sum-frequency generation spectroscopy

IR-vis sum-frequency generation spectroscopy is used to study the stretching vibration of hydrogen chemically bound to a graphene sheet prepared on an Ir (111) crystal surface. We observe two distinct resonances at 2563 and 2716cm−1. Similarly, lines at 1881 and 2027cm−1 are found after D atom adsorption. The assignment to C–H stretching vibrations is discussed in view of the propensity for dimer formation reported for hydrogen adsorbed on graphene. The lines are assigned to hydrogen bound in either ortho or para configuration to the hexagonal mesh of carbon atoms.

Vibrational spectroscopy studies of a pressure-induced disproportionation reaction of LaH 2

The pressure-induced disproportionation reaction of LaH 2 was investigated by infrared reflection and Raman measurements at ambient temperature. The relative reflection intensity in the 4000–6000 cm −1 region began to decrease significantly at a pressure of about 12 GPa and fell to 10% of the initial value at 20 GPa. Absorption peaks, which appeared around 1200 and 700 cm −1 at pressures above 14 GPa, were assigned to the hydrogen vibrations at the tetrahedral and octahedral sites of the fcc metal lattice, respectively. The peak frequencies measured in the 14–30 GPa range were similar to those observed in LaH 3. These infrared results indicated insulating LaH 3 precipitated from metallic LaH 2. Above 20 GPa, a Raman peak related to the hydrogen vibration in the octahedral sites appeared around 700 cm −1, and was likely due to lattice distortion. The disproportionation reaction of LaH 2 into LaH 2 + δ and solid solution LaH x ( x < 1 ) was confirmed.

Experimental evidence of librational vibrations determining the stability of calcium borohydride

The high energy of hydrogen vibrations in solids is the origin of their strong impact on thermodynamic properties. The peculiar structure of complex hydrides amplifies this impact. We shed light on the vibrational properties of three allotropes of Ca(BH4)2 using density-functional theory calculations, infrared spectroscopy, and inelastic neutron scattering. We show that the vibrational properties of Ca(BH4)2 depend on the specific phase and are hitherto the origin of their differences in stability.

Hydrogen Vibrational Excitation Spectra of CaF&lt;SUB&gt;2&lt;/SUB&gt;-Type Metal Hydrides Synthesized from Ti-Based BCC Solid Solution Alloys

Hydrogen vibrational excitation was studied for CaF2-type metal hydrides synthesized from Ti-based BCC solid solution alloys using inelastic incoherent neutron scattering (IINS). Ti1:0V1:1Mn0:9H4:5 and Ti0:7V1:2Cr1:1H4:8 showed IINS spectra similar to that reported for TiH2. The first three peaks were isolated but the higher excitation peaks were not clear. Analysis of the spectra using curve-fitting with Gauss functions revealed that the hydrogen vibration of Ti1:0V1:1Mn0:9H4:5 is harmonic but that of the Ti0:7V1:2Cr1:1H4:8 is deviated from harmonic, which reflects a trumpet-type potential. The relation between metal-hydrogen distance and vibrational excitation energy for the above two hydrides and Ti1:1Cr1:4Mo0:3H 5 was compared with a series of CaF2-type binary metal hydrides. All the hydrides of the Ti-based alloys had lower vibrational excitation energies than the binary metal hydrides for the corresponding metal-hydrogen distances. [doi:10.2320/matertrans.MA201014]

The molecular structure of the mineral beudantite PbFe3(AsO4,SO4)2(OH)6 – Implications for arsenic accumulation and removal

The objective of this research is to determine the molecular structure of the mineral beudantite using vibrational spectroscopy. Beudantite samples from different origins were studied by a combination of Raman and infrared spectroscopy.Observed bands are assigned to the stretching and bending vibrations of (SO4)2- and (AsO4)3- units, stretching and bending, stretching and bending vibrations of hydrogen bonded (OH)− ions and Fe3+–(O,OH) units. The approximate range of O–H⋯O hydrogen bond lengths is inferred from the Raman spectra. Raman spectra of crystalline beudantite and of the amorphous gel differ in that the beudantite spectrum is more complex, where bands are sharp and the degenerate bands of (SO4)2- and (AsO4)3- are split and more intense. Lower wavenumbers of δ H2O bending vibration in the spectrum of the amorphous gel may indicate the presence of weaker hydrogen bonds compared with those in beudantite. The formation of beudantite offers a mechanism for the removal of arsenic from the environment.

Dynamics of Distorted PO4 Modes and Hydrogen Modes in KDP/DKDP Mixed Crystals

The z(xy)-z Raman spectra of KDP/DKDP mixed crystals of the hydrogen and deuterium vibrations have been well reproduced by using a simple addition of KDP and DKDP spectra. The reciprocal half width γ−1 of the forbidden ν4 mode in x(zz)y Raman spectra in the paraelectric phase increases with increasing deuterium concentration just in the same way as the ferroelectric phase transition temperature T c. These results indicate that the local distortion of PO4 tetrahedron is strongly correlated with the T c in these hydrogen-bonded ferroelectrics.

Infrared absorption spectra of δ-AlOOH and its deuteride at high pressure and implication to pressure response of the hydrogen bonds

Infrared absorption spectra of δ-AlOOH and its deuterated form (δ-AlOOD) were measured at high pressure using a diamond anvil cell under a quasi-hydrostatic pressure condition using helium as a pressure-transmitting medium. Two absorption bands at 1180 cm−1and 1330 cm−1 involving vibrations of hydrogen and oxygen atoms shifted to higher frequencies with increasing pressure up to 10 and 12 GPa for δ-AlOOH and δ-AlOOD, respectively. In contrast, at higher pressures the two bands did not shift so much. The pressure-response on the infrared spectra has a close relationship to the symmetrization of the hydrogen bonds and change in the compressibility which was observed from X-ray diffraction measurements.

Isotope effects in the vibrational lifetime of hydrogen on germanium(100): Theory and experiment

Combining first-principles calculations and sum frequency generation spectroscopy, we elucidate the microscopic details in the relaxation of the stretching vibration of hydrogen adsorbed on Ge(100). The dominant decay channels involve energy transfer from the stretching to the hydrogen bending modes, with the remaining energy difference being transferred to or from substrate phonons. The coupling between stretching and bending modes is treated from first principles using the calculated multidimensional adiabatic potential energy surface, while the coupling to phonons is treated in perturbation theory. For a surface solely saturated with light hydrogen, we calculate a vibrational lifetime of 1.56 ns at 400 K, in good agreement with experiment, and find a similar temperature dependence of the lifetime in both experiment and theory. The calculations show that the stretching energy dissipates to a vibrational state involving four bending quanta of hydrogen, concurrently absorbing a thermally excited surface phonon related to the Ge dimer rocking mode. For a Ge surface saturated with a mixture of H and D, our experiments find that the relaxation rate of the H stretching vibration is markedly increased when compared to a surface saturated with H only. Experimentally, a single decay is observed although H and D atoms will statistically pair on the surface dimers. The vibrational lifetime of the Ge-H stretching mode is up to six times shorter in the presence of adsorbed D atoms. The calculated relaxation rates are consistent with the experimentally observed trend. The theoretical analysis shows that the breaking of symmetry within the Ge surface dimer due to coadsorption of D opens up further relaxation channels that involve absorption or emission of a substrate phonon at various energies. Moreover, the calculations predict an even shorter vibrational lifetime of the Ge-D stretch mode due to efficient coupling to the Ge dimer rocking mode.

Hydrogen Bonds and Vibrations of Water on (110) Rutile

We study the relation between the hydrogen bonding and the vibrational frequency spectra of water on the (110) surface of rutile (α-TiO2) with three structural layers of adsorbed water. Using ab initio molecular dynamics simulations at 280, 300, and 320 K, we find strong, crystallographically controlled adsorption sites, in general agreement with synchrotron X-ray and classical molecular dynamics simulations. We demonstrate that these sites are produced by strong hydrogen bonds formed between the surface oxygen atoms and the sorbed water molecules. The strength of these bonds is manifested by substantial broadening of the stretching mode vibrational band. The overall vibrational spectrum obtained from our simulations is in good agreement with inelastic neutron scattering experiments. We correlate the vibrational spectrum with different bonds at the surface to transform these vibrational measurements into a spectroscopy of surface interactions.

CARS microscopy of lipid stores in yeast: the impact of nutritional state and genetic background

AbstractWe have developed a protocol for sub‐micrometer resolved and chemically specific imaging of lipid storage in vivo employing coherent anti‐Stokes Raman scattering (CARS) microscopy of one of the most important model organisms Saccharomyces cerevisiae—the yeast cell. By probing the carbon–hydrogen vibration using the nonlinear process of CARS, lipid droplets in the yeast cells clearly appear, as confirmed by comparative studies on relevant labeled organelles using two‐photon fluorescence microscopy. From the images, unique quantitative data can be deduced with high three‐dimensional resolution, such as the volume, shape, number, and intracellular location of the neutral lipid stores. We exemplify the strength and usability of the method for two cases: the impact on lipid storage of the nutritional condition (starvation and type of carbon source available) as well as of genetic modification of two fundamental metabolic regulation pathways involving carbohydrate and lipid storage (BCY1 and DGA1, LRO1, ARE1/2 deletions), respectively. While the impact of carbon source on the total cellular lipid volume was minimal, long‐term starvation induces a significant accumulation of lipid droplets. We also confirm that the lipid‐storage‐deficient mutant is indeed unable to synthesize lipid droplets, and that the inability of the bcy1‐mutant to store carbohydrates is compensated by a two‐fold increase in stored neutral lipids. We note that there is a significant cell‐to‐cell variability in neutral lipid storage in general, i.e. that there is a correspondence to the noise found for gene expression also in lipidomics. Copyright © 2009 John Wiley &amp; Sons, Ltd.

Resonant Interaction between Hydrogen Vibrational Modes in AlSb:Se

Vibrational modes and their interactions affect numerous physical processes in condensed-matter systems. In the present work, hydrogen vibrations in Se-doped AlSb were investigated with first-principles calculations. Vibrational frequencies were calculated for the longitudinal, transverse, wag (bending), and stretch modes of the Al-H complex. The Al-H stretch mode interacts with a combination mode involving a wag overtone and transverse fundamental. This resonant interaction yields vibrational states that are linear superpositions of the stretch mode and the combination mode. The spatial extent of such excitations is significantly larger than that of a local vibrational mode.

THERMODYNAMICS AND HYDROGEN STORAGE ABILITY OF BINARY HYDROGEN + HELP GAS CLATHRATE HYDRATE

Storage of hydrogen as hydrogen hydrate is a promising alternative technology to liquefied hydrogen at cryogenic temperatures or compressed hydrogen at high pressures. In this paper, computer simulation is performed based on the solid solution theory of clathrates of van der Waals and Platteeuw with some modifications that include in particular the account of multiple cage occupancies and host relaxation. The quasiharmonic lattice dynamics method employed here gives the free energy of clathrate hydrate to first order in the anharmonicity of intermolecular potential and permits to take into account quantum zero-point vibration of host lattice and hydrogen in the cages. It is employed to study the thermodynamic functions of binary (mixed) H 2– CH 4 hydrates of cubic structure II (sII) and hexagonal structure H (sH). It is shown that at divariant equilibrium "gas phase–gas hydrate" with increasing pressure the filling of large cavities by hydrogen proceeds gradually from single filling to the maximal number of hydrogen molecules in clusters included in large cages (four in sII and five in sH) preserving stability of the hydrogen–methane hydrates sII and sH. The results show that mass fraction of hydrogen in the mixed sH hydrate is significantly lower than in the mixed sII hydrate. Pressure of monovariant equilibrium " IceI h–gas phase–mixed sII hydrate" with increasing methane concentration in the gas phase lowers in comparison with the pressure of pure hydrogen hydrate formation. For the mixed hydrogen + methane sH hydrates, it was demonstrated that thermodynamic stability depends on the filling degree of small cavities by methane molecules and stability area shifts to lower pressure with increasing filling.

Preparation and optical properties of NdH3 and EuH2 films

Thin epitaxial films of neodymium and europium have been grown onto CaF2(111). The structural surface analysis reveals a textured character of the Eu samples consisting of three domains, each tilted by 60°. Auger electron spectroscopy has been performed to study the influence of a buffer layer on the protective properties of the palladium cap layer. After loading with hydrogen, the optical properties of the ferromagnetic semiconductors NdH3−δ and EuH2 were determined in the infrared and visible spectral range. A comparison of hydrogenated and deuterated samples clearly associates the phonons in the transmission spectra in the infrared to hydrogen vibrations. Transmission measurements in the visible spectral range yield the optical band gaps. The values of those gaps and the characteristics of the absorption edges are discussed in the context of their participating electronic transitions.

ESI MS, spectroscopic and semiempirical characterization of a macrobicyclic complex with Er (III) cation

Erbium cryptate [(MSB-H+NO 3+H 2O) Er] NO 3 has been synthesized as a result of the Schiff base condensation and investigated by FT-IR, ESI MS and EPR methods. In the ESI MS spectrum of this complex [(MSB-H+NO 3+H 2O) Er] NO 3 in the range of cv = 10–30V two main signals at m/z = 422 and m/z = 842 were observed corresponding to the [(MSB-H) Er] 2+ and [(MSB-2H) Er] + fragmentary cations, respectively. Besides these main peaks, a low intensity signals at m/z = 903 and m/z = 921 assigned to the [(MSB-H+NO 3) Er] + and [(MSB-H+NO 3+H 2O) Er] + complexes were also found. FT-IR spectrum revealed a broad band at 3403 cm −1 assigned to the ν(OH) vibrations of hydrogen bonded water molecule within the 1:1 macrobicyclic Schiff base-Er 3+ complex as well as the bands at 1335 cm −1 and 1355 cm −1 assigned to the ν ( NO 3 - ) vibrations of both bonded and non-bonded with the metal cations nitrate groups, respectively. DTA-TG analysis confirmed the presence of one water molecule in the complex. Full geometry optimization and heat of formation calculations of macrobicyclic Schiff base ligand and its complexes including nitrate anion and one water molecule were carried out. A comparison of these data suggests that the complexation of Er 3+ cation by the macrobicyclic Schiff base molecule with the involvement of water molecule is less energetically favourable. EPR measurements confirmed the presence of one Er 3+ cation in the complex structure. Computer simulation of the recorded EPR spectra revealed the presence of low symmetry at the Er ion site. The semiempirical MM/AM1d calculations indicated an asymmetrical location of the Er 3+ cation within the complex structure.

Ab Initio Calculations of Thermodynamic Hydricities of Transition-Metal Hydrides in Acetonitrile

Theoretical hydricities calculated by different methods are compared with all the available experimental values for the Co- and Ni-group metal hydrides in acetonitrile. It is found that the B3P86 method employing a sufficiently flexible basis set in combination with the C-PCM solvent model can accurately predict the hydricity with a precision of 2.0 kcal/mol. The same method can also accurately predict the acidities of the metal−hydrogen bond and the redox potentials of the corresponding metal hydrides with precisions of 1.9 pKa units and 0.07 V, respectively. On the other hand, an ONIOM method where the core layer is treated with the CCSD(T) method fails to predict the hydricity of transition-metal hydrides, possibly because the electronic effects of the outer layer are not accurately estimated with the low-level theory in the ONIOM partitioning scheme or because the basis sets in the ONIOM methods are not sufficiently flexible. As to the periodical trends, it is found that for the Co-group metal hydrides, the hydricities increase in the order second row < third row < first row. For the Ni-group metal hydrides, the hydricities increase in the order second row ≈ third row ≪ first row. As to the effects of the phosphine ligands, it is found that a dual-parameter equation can quantitatively predict the hydricities, where the two parameters are the NBO charge of the phosphorus and the natural bite angle of the diphosphine. Finally, no correlation is found between the hydricity and the metal−hydrogen vibration frequency or the hydrogen chemical shift. Therefore, it is not reliable to use any vibrational spectrum or proton NMR method to estimate the hydricity of transition-metal hydrides.