Deuterium Hydride Research Articles

Self-diffusion of liquid deuterium hydride and liquid tritium.

We present a quasi-elastic neutron scattering study of liquid deuterium hydride carried out using the Disk Chopper Spectrometer at the National Institute of Standards and Technology. Under saturated vapor pressure, the self-diffusion constant of deuterium hydride obeys an Arrhenius law D=D0exp-EA/kBT, where the prefactor D0 is given by D0=9.5±1.2Å2/ps and the activation energy is given by EA = 58 ± 2K. We apply the quantum law of corresponding states to the known diffusion constants of the hydrogen isotopologues. From this application, we estimate that D0≈9.1Å2/ps and EA ≈ 75K in liquid tritium. Young's theory of quantum-mechanical effects in van der Waals fluids [Young, Phys. Rev. A 23, 1498 (1981)] is shown to apply to the diffusion constants of the liquid hydrogens. Our results underscore the importance of nuclear quantum effects in shaping the properties and behavior of the hydrogen isotopologues.

Warm dust surface chemistry

Context.Molecular hydrogen (H2) is the main constituent of the gas in the planet-forming disks that surround many pre-main-sequence stars. H2can be incorporated in the atmosphere of the nascent giant planets in disks. Deuterium hydride (HD) has been detected in a few disks and can be considered the most reliable tracer of H2, provided that its abundance throughout the disks with respect to H2is well understood.Aims.We wish to form H2and HD efficiently for the varied conditions encountered in protoplanetary disks: the densities vary from 104to 1016cm−3; the dust temperatures range from 5 to 1500 K, the gas temperatures go from 5 to a few 1000 Kelvin, and the ultraviolet radiation field can be 107stronger than the standard interstellar field.Methods.We implemented a comprehensive model of H2and HD formation on cold and warm grain surfaces and via hydrogenated polycyclic aromatic hydrocarbons in the physico-chemical code PROtoplanetary DIsk MOdel. The H2and HD formation on dust grains can proceed via the Langmuir-Hinshelwood and Eley-Ridel mechanisms for physisorbed or chemisorbed H (D) atoms. H2and HD also form by H (D) abstraction from hydrogenated neutral and ionised PAHs and via gas phase reactions.Results.H2and HD are formed efficiently on dust grain surfaces from 10 to ~700 K. All the deuterium is converted into HD in UV shielded regions as soon as H2is formed by gas-phase D abstraction reactions. The detailed model compares well with standard analytical prescriptions for H2(HD) formation. At low temperature, H2is formed from the encounter of two physisorbed atoms. HD molecules form on the grain surfaces and in the gas-phase. At temperatures greater than 20 K, the encounter between a weakly bound H- (or D-) atom or a gas-phase H (D) atom and a chemisorbed atom is the most efficient H2formation route. H2formation through hydrogenated PAHs alone is efficient above 80 K. However, the contribution of hydrogenated PAHs to the overall H2and HD formation is relatively low if chemisorption on silicate is taken into account and if a small hydrogen abstraction cross-section is used. The H2and HD warm grain surface network is a first step in the construction of a network of high-temperature surface reactions.

Visualization study of thermal counterflow of superfluid helium in the proximity of the heat source by using solid deuterium hydride particles

An experimental investigation of steady-state thermal counterflow of superfluid ${}^{4}$He indicates that, in the range of investigated parameters, interactions between flow-probing particles and tangles of quantized vortices are appreciably influenced not only by the tangle geometry but also by the particle inertia.

Cold quantum-controlled rotationally inelastic scattering of HD with H2 and D2 reveals collisional partner reorientation.

Molecular interactions are best probed by scattering experiments. Interpretation of these studies has been limited by lack of control over the quantum states of the incoming collision partners. We report here the rotationally inelastic collisions of quantum-state prepared deuterium hydride (HD) with H2 and D2 using a method that provides an improved control over the input states. HD was coexpanded with its partner in a single supersonic beam, which reduced the collision temperature to 0-5 K, and thereby restricted the involved incoming partial waves to s and p. By preparing HD with its bond axis preferentially aligned parallel and perpendicular to the relative velocity of the colliding partners, we observed that the rotational relaxation of HD depends strongly on the initial bond-axis orientation. We developed a partial-wave analysis that conclusively demonstrates that the scattering mechanism involves the exchange of internal angular momentum between the colliding partners. The striking differences between H2/HD and D2/HD scattering suggest the presence of anisotropically sensitive resonances.

Design optimization and performances of New Sorgentina Fusion Source (NSFS) supporting materials research

In the framework of fusion materials research, a neutron source has been considered a key installation to support EU plan toward DEMO reactor design. IFMIF facility being the present proposal, a pragmatic approach to EU fusion roadmap timeline considers complementary solutions mandatory, within a shared strategy. New Sorgentina Fusion Source (NSFS) has been recently proposed in order to populate an engineering database through materials irradiation tests. Proven technology of D–T neutron generators is implemented together with ion source and accelerator devices currently used in neutral injection systems at experimental tokamaks. Deuterium and tritium enriched hydride is on-line reloaded by impinging D–T beams via ion implantation onto a high-speed rotating target – D–T retention is allowed through temperature control. Hydride metal layer is re-deposited increasing plant availability factor. Target design is proposed to cope with thermal transients and mechanical loads. Solutions to thermal fatigue concerns are presented. Irradiation capability is then enhanced attaining relevant materials exposure. Main facility characteristics are provided as well as thermal and mechanical issues.

Classical calculations of radiative association in absence of electronic transitions

A formula for the cross section of radiative association where no electronic transitions take place is derived and tested for diatomic molecules. The approach is based on classical mechanics and therefore it is valid for direct, i.e., non-resonant, radiative association. For the formation of carbon monoxide (CO) and the cyano radical (CN), in the X1Σ+ and A1Π states, respectively, the treatment reproduces the baselines of the cross sections obtained using quantum mechanical perturbation theory. The method overestimates the formation cross section of potassium sodide (NaK) by about 8%. For the lower mass diatoms hydrogen fluoride (HF) and deuterium hydride (HD), the formula overestimates the cross sections by 12% and 60%, respectively. The formula can be used alone for estimates of radiative association rate constants, or in combination with Breit-Wigner theory to include resonance contributions.

Molecular Hydrogen Tweezers: Structure and Mechanisms by Neutron Diffraction, NMR, and Deuterium Labeling Studies in Solid and Solution

The mechanism of reversible hydrogen activation by ansa-aminoboranes, 1-N-TMPH-CH(2)-2-[HB(C(6)F(5))(2)]C(6)H(4) (NHHB), was studied by neutron diffraction and thermogravimetric mass-spectroscopic experiments in the solid state as well as with NMR and FT-IR spectroscopy in solution. The structure of the ansa-ammonium borate NHHB was determined by neutron scattering, revealing a short N-H···H-B dihydrogen bond of 1.67 Å. Moreover, this intramolecular H-H distance was determined in solution to be also 1.6-1.8 Å by (1)H NMR spectroscopic T(1) relaxation and 1D NOE measurements. The X-ray B-H and N-H distances deviated from the neutron and the calculated values. The dynamic nature of the molecular tweezers in solution was additionally studied by multinuclear and variable-temperature NMR spectroscopy. We synthesized stable, individual isotopic isomers NDDB, NHDB, and NDHB. NMR measurements revealed a primary isotope effect in the chemical shift difference (p)Δ(1)H(D) = δ(NH) - δ(ND) (0.56 ppm), and hence supported dihydrogen bonding. The NMR studies gave strong evidence that the structure of NHHB in solution is similar to that in the solid state. This is corroborated by IR studies providing clear evidence for the dynamic nature of the intramolecular dihydrogen bonding at room temperature. Interestingly, no kinetic isotope effect was detected for the activation of deuterium hydride by the ansa-aminoborane NB. Theoretical calculations attribute this to an "early transition state". Moreover, 2D NOESY NMR measurements support fast intermolecular proton exchange in aprotic CD(2)Cl(2) and C(6)D(6).

Tetrahydrometalate Species VH2(H2), NbH4, and TaH4: Matrix Infrared Spectra and Quantum Chemical Calculations

Laser ablated V, Nb, and Ta atoms react with molecular hydrogen in excess neon at 4 K to give vanadium, niobium, and tantalum dihydrides that further react with H(2) to form VH(2)(H(2)), NbH(4), and TaH(4). The reaction products are identified by deuterium and deuterium hydride isotopic substitution. DFT and CCSD theoretical calculations are used to predict energies, geometries, and vibrational frequencies for these novel metal hydrides complex and molecules. The vanadium dihydride hydrogen complex, VH(2)(H(2)), is identified, while the niobium and tantalum tetrahydrides, NbH(4) and TaH(4,) with D(2d) symmetry structures are confirmed. Reactions of group 5 metal atoms with H(2) condensing in solid hydrogen gave VH(2)(H(2)) and the higher tetrahydride-hydrogen complexes NbH(4)(H(2))(4) and TaH(4)(H(2))(4).

Short pulse laser-induced dissociation of vibrationally cold, trapped molecular ions

An electrostatic trapping scheme for use in the study of light-induced dissociation of molecular ions is outlined. We present a detailed description of the electrostatic reflection storage device and specifically demonstrate its use in the preparation of a vibrationally cold ensemble of deuterium hydride (HD+) ions. By interacting an intense femtosecond laser with this target and detecting neutral fragmentation products, we are able to elucidate previously inaccessible dissociation dynamics for fundamental diatomics in intense laser fields. In this context, we present new results of intense field dissociation of HD+ which are interpreted in terms of recent theoretical calculations.

Reverse Spillover of Hydrogen on Carbon-Based Nanomaterials: Evidence of Recombination Using Isotopic Exchange

The hydrogen spillover phenomenon at ambient temperature is of interest in the development of adsorbents for storage applications. The mechanism of hydrogen spillover is studied using equilibrium dosing of the deuterium hydride molecule. Temperature programmed desorption spectra for both primary and secondary spillover materials, with the deuterium peak appearing first, have supported partitioning of the desorption behavior into reverse spillover and recombination directly from the atomic receptor. Desorption kinetics are faster relative to adsorption for hydrogen and deuterium on all carbon-based adsorbents in the study. Diffusion time constants are computed using a surface diffusion model based on Fick’s second law. Kinetic data are studied for pressures from atmospheric to 100 atm and equilibrium adsorbed amounts to 5.5 mmol/g. Values follow an inverse relationship with amount and are 2 orders of magnitude higher (10−4 s−1) than those reported for nitrogen physisorption on carbon adsorbents. Adsorption...

The aftermath of the first stars: massive black holes

We investigate the evolution of the primordial gas surrounding the first massive black holes formed by the collapse of Population III stars at redshifts z≳ 20. Carrying out three-dimensional hydrodynamical simulations using gadget, we study the dynamical, thermal and chemical evolution of the first relic H ii regions. We also carry out simulations of the mergers of relic H ii regions with neighbouring neutral minihaloes, which contain high-density primordial gas that could accrete on to a Population III remnant black hole. We find that there may have been a significant time delay, of the order of ∼108 yr, between black hole formation and the onset of efficient accretion. The build-up of supermassive black holes, believed to power the z≳ 6 quasars observed in the Sloan Digital Sky Survey, therefore faces a crucial early bottleneck. More massive seed black holes may thus be required, such as those formed by the direct collapse of a primordial gas cloud facilitated by atomic line cooling. The high optical depth to Lyman–Werner (LW) photons that results from the high fraction of H2 molecules that form in relic H ii regions, combined with the continued formation of H2 inside the dynamically expanding relic H ii region, leads to shielding of the molecules inside these regions at least until a critical background LW flux of ∼10−24 erg s−1 cm−2 Hz−1 sr−1 is established. Furthermore, we find that a high fraction of deuterium hydride (HD) molecules, XHD≳ 10−7, is formed, potentially enabling the formation of Population II.5 stars, with masses of the order of ∼10 M⊙, during later stages of structure formation when the relic H ii region gas is assembled into a sufficiently deep potential well to gravitationally confine the gas again.

The Electron Excited Ultraviolet Spectrum of HD: Cross Sections and Transition Probabilities

We have analyzed the high-resolution ultraviolet (UV) emission spectrum of molecular deuterium hydride (HD) excited by electron impact at 100 eV under optically thin, single-scattering experimental conditions. The high-resolution spectrum (FWHM=160 mA) spans the wavelength range from 900 to 1650 A and contains the two Rydberg series of HD: (sup 1)Sigma(sub u)(sup +)1s(sigma), np(si n=2, 3, 4) --> X(sup 1)Sigma(sub g)(sup +) and (sup 1)Pi(sub u)(sup +)1s(sigma), np(pi)(C,D,D',D'', n=2, 3, 4, 5) -->X(sup 1)Sigma(sub g)(sup +). A model spectrum of HD, based on newly calculated tra rovibrational coupling for the strongest band systems, B (sup 1)Sigma(sub u)(sup +)-X(sup 1)Sigma(sub g)(sup +),B'(sup 1)Sigma(sub g)(sup +)-X(sup 1)Sigma(sub g)(sup +),C(sup 1)Pi(sub u)-X(sup 1)Sigm sections for direct excitation at 100 eV of the B (sup 1)Sigma(sub u)(sup +), B' (sup 1)Sigma(sub u)(sup +), C(sup 1)Pi(sub u), and D(sup 1)Pi(sub u) states were derived from a model analysis of the state. The absolute cross section values for excitation to the B (sup 1)Sigma(sub u)(sup +), B' (sup 1)Sigma(sub u)(sup +), C(sup 1)Pi(sub u), and D(sup 1)Pi(sub u) states were found to be (2.57+/-0. and (0.17+/-0.04)x10(exp -17) sq cm, respectively. We have also determined the dissociative excitation cross sections at 100 eV for the emission of Ly(alpha) at 1216 A and Ly(Beta) at 1025 A lines, which are (7.98+/-1.12)x10(exp -18) and (0.40+/-0.10)x10(exp -18) sq cm, respectively. The summed excitation function of the closely spaced pair of lines, H Ly(alpha) and D Ly(Beta), resulting from excitation of HD, has been measured from the threshold to 800 eV and is analytically modeled with a semiempirical relation. The model cross sections are in good agreement with the corrected Ly(alpha) cross sections of Mohlmann et al. up to 2 keV. Based on measurements of H, D (2s) production cross section values by Mohlmann et al., the H, D (n=2) cross section is estimated to be 1.6 x 10(exp -17) sq cm at 100 eV.

Generating Low-Temperature Layers with Infrared Heating

Cryogenic targets for the National Ignition Facility require uniform solid layers inside spherical capsules at temperatures ~1.5 K below the triple point of hydrogen. Uniform layers have been successfully formed near the triple point. However, upon subsequent cooling the layers degrade. We report here recent attempts to form uniform deuterium hydride (HD) layers 1.5 K below the triple point using infrared (IR) radiation. Pumping the IR collisionally induced vibration-rotation band of solid HD contained inside a transparent plastic shell generates a volumetric heat source in the HD lattice. This in turn allows the formation of a spherical crystalline shell of HD inside the transparent plastic shell. HD layers ~50 μm thick have been formed near the triple point and slowly cooled 1.5 K under high IR power without layer degradation.

Diffusive motions in HD films physisorbed on graphite

High-resolution quasielastic neutron scattering was used to study diffusive motions in two-dimensional liquid and solid phases of deuterium hydride submonolayers adsorbed on graphite (Papyex). For the first time it could be unambiguously clarified that the novel reentrant fluid phase at the commensurate–incommensurate transition has the character of a viscous fluid.

Matrix Infrared Spectra and DFT Calculations of the Reactive MHx (x = 1, 2, and 3), (H2)MH2, MH2+, and MH4- (M = Sc, Y, and La) Species

Laser-ablated Sc, Y, and La react with molecular hydrogen to give MH, MH2+, MH2, MH3, and MH4- (M = Sc, Y, and La) during condensation in excess argon for characterization by matrix infrared spectroscopy. Annealing forms the dihydrogen complex (H2)MH2, which can be reduced to MH4- by electron capture. The (HD)MHD complex exchanges hydrogen positions on broadband photolysis to form primarily the (D2)MH2 complex. Doping the samples with CCl4 to capture ablated electrons markedly increases the MH2+ infrared band intensities and decreases the MH4- absorptions. Further annealing produces higher (H2)2MH2 complexes, which also exchange hydrogen positions. The reaction products are identified by deuterium and deuterium hydride isotopic substitution. DFT and MP2 theoretical calculations are employed to predict geometries and vibrational frequencies of these novel molecules, complexes, anions, and cations. Charged species from laser-ablation contribute more to the spectra of group 3 reaction products than for any o...

The synthesis and reactivity of a molybdenum (IV) stretched-dihydrogen complex.

Reaction of [Mo(NPh)(PMe3)3(o-(Me3SiN)2C6H4)] (1) with molecular hydrogen (ca. 1 atm) at -10 degrees C in toluene-d8 results in the formation of dihydrogen complex [Mo(NPh)(PMe3)2(H2)(o-(Me3SiN)2C6H4)] (2) by 1H and 31P NMR spectroscopy. In solution at -50 degrees C 1 and 2 are present in a 1:3 ratio, respectively. The nature of dihydrogen ligand bonding in 2 was probed by T1 analysis and analysis of the JH-D coupling constant in the deuterium hydride isotopomer of 2 giving H-H distances of 1.18 A and 1.17 A, respectively. When allowed to warm to 30 degrees C, 2 reacts affording [Mo(NPh)(PMe3)3(o-(Me3SiN)(NH)C6H4)] (3) over a 1 h period. The X-ray structures of 1 and 3 are reported.

The HD–He complex: Interaction-induced dipole surface and infrared absorption spectra

The collision-induced dipole surface of an HD molecule interacting with an He atom is derived from the ab initio dipole data of the H2–He complex [Gustafsson et al., J. Chem. Phys. 113, 3641, (2000)]. Collision-induced absorption spectra of gaseous mixtures of deuterium hydride and helium in the rotational and fundamental bands of HD are calculated, for comparison with an existing measurement taken at a temperature of 77 K. To that end, we integrate the close-coupled, radial Schrödinger equations, accounting for the anisotropy of the HD–He interaction potential. The computed absorption spectra generally agree reasonably well with the observed spectral profiles and intensities of the collision-induced spectra. We also consider the interference phenomena of the HD permanent dipole with the interaction-induced, supramolecular dipole by computing the wings of various R(j) lines and of the P1(1) line in single, binary collision limit. For comparison, the line broadening and shift for the P and R line shape parameters are also computed using the impact approximation. The close-coupled treatment of our calculation of the spectral profiles accounts for rotational level mixing in a nonperturbative manner. The treatment is fully quantum-mechanical and takes into account single binary collisions of HD and He.

Forming Uniform HD Layers in Shells Using Infrared Radiation

Generating a volumetric heat source in solid deuterium hydride, HD, allows the formation of a spherical crystalline shell of HD inside a transparent plastic shell. Pumping the infra-red (IR) collisionally induced vibration-rotation band of solid HD contained inside a transparent plastic shell generates the volumetric heat source in the HD lattice. HD layers 150 – 250 μm thick formed near the triple point have a surface roughness rms between 1–3 μm and become rougher with decreasing temperature. Solid growth dynamics have a significant impact on the quality of the resultant layer.

Thermal Rate Constant and Branching Ratio for CN + HD → HCN/DCN + D/H from T = 293 to 375 K

The reaction rate constant for the cyano (CN) radical with deuterium hydride (HD) has been determined over the temperature range from 293 to 375 K. As well, the branching ratio for the partitioning into HCN + D or DCN + H has also been measured. The CN radical was detected by time-resolved near-infrared absorption spectroscopy using the CN (A{sup 2}{Pi} {l_arrow} X{sup 2}{Sigma}) (2,0) band near 789.5 nm while the HCN molecule was monitored by time-resolved infrared absorption spectroscopy using the HCN(001) {l_arrow} (000) {upsilon}{sub 3} fundamental band near 3.0 {micro}m. Both species were monitored following the same photolysis laser pulse used to generate the CN radical. The measurements were carried out in low pressures of Ar or He as carrier gas. The frequencies and structure of the transition states for all four isotopomers for CN + H{sub 2} were calculated using ab initio quantum chemistry methods and a normal-mode analysis. Reasonable agreement was found between the experimental results and the rate constants predicted by conventional transition state theory using the theoretical transition state properties. These measurements should provide for an interesting test for theoretical predictions of thermal rate constants for this prototypical four-atom reaction system.

Heat capacity, adsorption isotherms, and quasielastic neutron scattering measurements of bilayer deuterium hydride adsorbed on graphite.

Bilayer films of deuterium hydride (HD) adsorbed on exfoliated graphites have been studied using heat capacity, adsorption isotherms, and quasielastic neutron scattering (QENS) measurements. The second layer of HD shows solid ($S$), liquid ($L$), and gaseous ($G$) [vapor ($V$)] phases, with two-dimensional (2D) characteristics. We determined the $S\ensuremath{-}L\ensuremath{-}V$ triple line at ${T}_{t}(2\mathrm{D})=8.44$ K, and the $L\ensuremath{-}V$ critical temperature at ${T}_{c}(2\mathrm{D})=11.45$ K. QENS identified the $L$ phase and measured its translation diffusion coefficient ${D}_{T}(\ensuremath{\approx}{10}^{\ensuremath{-}5} {\mathrm{cm}}^{2}{\mathrm{s}}^{\ensuremath{-}1} \mathrm{at} 9.25 \mathrm{K})$. Isosteric heats, latent heat, and entropy change at melting, and solid Debye temperatures are calculated. The results are used to construct a general graph of critical and triple points of adsorbed gases as a function of their quantum parameter.