The formation and decomposition kinetics of alkylidynes on Pt(111)

The formation and decomposition kinetics of ethylidyne and propylidyne on Pt(111), were studied using static secondary ion mass spectrometry and temperature programmed desorption. For the maximum amounts of dissociatively adsorbed ethylene and propylene formed during adsorption at 200 K and subsequent temperature programmed desorption, the following activation energies (E) and pre-exponential factors (A) are determined: (a) for ethylidyne formation: E = 17±1 kcal mol⁻¹ and A = 1×10^12±1 s⁻¹; (b) ethylidyne decomposition: E = 27 ±2 kcal mole⁻¹ and A = 6×10^11±1 s⁻¹; (c) propylidyne formation: E = 17.5 ± 2 kcal mol⁻¹ and A = 7×10^12±1 s⁻¹; and (d) propylidyne decomposition: E = 22.5±2 kcal mol⁻¹ and A = 4×10^{11 ± 1} s⁻¹.     

Hydrogen isotope exchange in a coverage obtained on Ir(111) by ethylene adsorption

HREELS and SIMS studies of hydrogen isotopc exchange in a coverage obtained on Ir(111) by ethylene adsorption are carried out at 180–450 K and at a hydrogen (deuterium) pressure up to 8×10⁶ Pa. The ethylidyne species have shown a high stability towards hydration and structural changes upon hydrogen (deuterium) exposures. Under these conditions hydrogen exchange in the methyl groups is a slow process. With increasing temperature the hydrogen exchange in the decomposition products of ethylidyne (C₂H species) is quick and depends on the exchanged amount of atomically adsorbed hydrogen.     

Thermal release of trapped deuterium from silica injected by 80-keV D+ ion implantation and RF D2 plasma

When silica is irradiated by 80-keV D⁺ ions or RF plasma of D₂ gas, deuterium is trapped in the silica forming Si-OD bonds. The deuterium, trapped as OD bonds, is desorbed from the silica upon heating to form some release products. The thermal detrapping process corresponds to decrease of OD bonds and was studied by measurement of infrared Fourier transform spectroscopy (FTIR). The release products HDO, D₂O, HD, and D₂ were measured by quadrupole mass spectroscopy (QMS). The detrapping and release processes of trapped deuterium were studied by simultaneous measurement of FTIR and QMS. Since the release spectra of HDO, D₂O, HD, and/or D₂ correspond to the decrease spectra of OD bonds, these release products are formed by thermal decomposition of OD bonds. The formation of water (HDO, D₂O) and hydrogen (HD, D₂) depends upon concentration of pre-existing OH bonds and deuterium injection methods (80-keV D⁺ implantation or RF D₂ plasma irradiation).     

The room temperature phase of Propene on Rh(111): A caveat on thermal processing for the production of adsorbed phases at definite temperatures

Hydrocarbon phases from the thermal processing of low temperature adsorption of propene on Rh(111) and those from direct adsorption at particular temperatures were characterized by HREELS and were found to show differences. The phase from direct adsorption at room temperature contains C_xH species and ethylidyne which shows a better bond breaking ability than the room temperature phase produced by thermal processing which contains ethylidyne, propylidyne and di-σ adsorbed propene. The use of the phase from direct adsorption at room temperature, especially the low coverage phase, in comparison with similarly prepared phases on Ru(001), Ir(111), Ni(111), Pd(111) and Pt(111) shows a correlation on bond breaking ability that agrees with Sinfelt's correlation of the hydrogenolysis activity of the group 7–10 metals. This suggests that the room temperature phase of an alkene on a surface can be used to predict the hydrogenolysis activity of that surface.     

Real‐time measurement of H/D exchange in a microdialysis Raman quartz cell

We present here a novel quartz cell for monitoring H/D exchange in biomolecules using Raman spectroscopy. This cell is combined with a syringe to pump heavy water through a hollow microdialysis fibre, which is inserted into the cell. The deuterium efflux into the sample has been studied as a function of the molecular weight cut‐off of the microdialysis fibre and compared with other microcell systems comprising conventional glass capillaries. The fastest D₂O efflux that we have obtained (k_d = 0.38 ± 0.008 min⁻¹) permits to measure exchange rates of 2.5 min⁻¹ or less. Application of this cell to deuterium exchange in glyceraldehyde‐3‐phosphate dehydrogenase reveals a class of H‐atoms highly resistant to deuteration, which is consistent with a previous infrared study on this protein. Copyright © 2009 John Wiley & Sons, Ltd.     

Hydrogen–Deuterium Exchange Reaction of 2-Benzylthio-5-Methyl-1,2,4-Triazolo[1,5-a]Pyrimidine Under Basic Conditions

Hydrogen–deuterium (H–D) exchange usually happens between D₂O/CD₃OD solvent and N-heterocyclic compounds in the presence of a base. 2-Benzylthio-5-methyl-1,2,4-triazolo[1,5-a]pyrimidine (BMTP) is an important intermediate for the synthesis of triazolopyrimidines with bioactivities. No exchange was observed when BMTP was dissolved in a CD₃OD solvent. However, a significant H–D exchange was observed after a small amount of NaOD had been added to the solution. According to the time-varying proton intensity, the rates (k _ex) of H–D exchange were achieved under various temperatures and different amounts of NaOD. The results showed that the H–D exchange rates of H3, H4, and H5 were different under identical conditions, but were enhanced with increasing temperature and concentration of NaOD. A mechanism of H–D exchange that might be instructive in the ring-open reaction of 1,2,4-triazolo[1,5-a]pyrimidine derivatives was proposed.     

A molecular-beam investigation of the scattering,adsorption and absorption of H2 and D2 from/on/in Pd(111)

H₂ and D₂ are scattered from clean Pd(111) and a saturated chemisorption layer in a highly specular distribution. Evidence for an ordering of the adiayer with increasing coverage is seen. The hydrogen-deuterium exchange occurs via a Langmuir-Hinshelwood mechanism, and the temperature dependence of the rate of HD production can be understood without assuming an activation energy for equilibration. Lock-in and wave-form analyses of scattered H₂ + D₂ mixed beams show that equilibrium between adsorbed hydrogen and deuterium and that dissolved just below the surface is reached rapidly at temperatures above 300 K.     

Hydrogen bond and exchange interaction in the (CuSO<Subscript>4</Subscript>)(en)·2H<Subscript>2</Subscript>O and (CuSO<Subscript>4</Subscript>)(en)·2D<Subscript>2</Subscript>O organometallic compounds

The influence of the replacement of hydrogen with deuterium in molecules of water of crystallization in the structure of the (CuSO₄)(en) · 2H₂O and (CuSO₄)(en)·2D₂O organometallic compound molecules on exchange interaction between copper ions was studied. The X-ray structural data and the data on angular anisotropy of the effective g-factor of Cu²⁺ ions in both compounds show that distortions of the initial structure caused by deuteration are minimum. A comparative analysis of the width of the exchange coupled EPR lines of the two compounds is indicative of a decrease in the exchange parameter in the deuterated sample, which substantiates the participation of H-bonds in exchange interactions in the systems studied.     

Dissolution of deuterium into proton conductor SrCe0.95Yb0.05O3−δ

The incorporation of deuterium in a perovskite-type oxide SrCe_0.95Yb_0.05O_3−δ was confirmed and its concentration was measured using a secondary ion mass spectrometer. The deuterium was absorbed in an atmosphere of O₂ and D₂O at a temperature range of 700–800°C. The concentration of deuterium was found to be 0.01 to 0.05 mol in one mole of SrCe_0.95Yb_0.05O_3−δ. This is remarkably large compared to the solubility of hydrogen in other oxide.     

Influence of epithermal muonic molecule formation on kinetics of the μCF processes in deuterium

The non-resonant formation of ddμ molecules in the loosely bound state in collisions of non-thermalized dμ atoms with deuterium molecules D₂ has been considered. The process of such a?type is possible only for collision energies exceeded the ionization potential of D₂. The calculated rates of ddμ formation in the above-threshold energy region are about one order of magnitude higher than obtained earlier. The role of epithermal non-resonant μ-molecule formation for the kinetics of μCF processes in D₂ gas was studied. It was shown that the non-resonant ddμ formation by dμ atoms accelerated during the cascade can be directly observed in the neutron time spectra at very short initial times.     

Effect of subsurface boron on photoluminescence from silicon nanocrystals

Silicon (Si) nanocrystals (NCs) less than 5 nm in diameter are grown on SiO₂ surfaces using hot wire chemical vapor deposition in an ultrahigh vacuum chamber and the dangling bonds are passivated using atomic deuterium. The passivated NCs are subsequently exposed to BD_x radicals formed by dissociating deuterated diborane (B₂D₆) over a hot tungsten filament and photoluminescence quenching is observed. Temperature programmed desorption spectra reveal the presence of additional D₂ desorption peaks beyond those found for surfaces that have only been passivated by atomic deuterium. The additional peaks appear at lower temperatures and this can be attributed to deuterium desorption from surface Si atoms bonded to subsurface boron atoms. The subsurface boron likely enhances nonradiative Auger recombination leading to photoluminescence quenching.     

低温下氘分子红外吸收特性研究

采用基于第一性原理的从头计算单双取代耦合簇方法并结合cc-PVTZ基组,计算了处于基态的(D2)3分子两种不同构型(D2d和D2h)的各种能量模式及其对应的红外谱图.利用自主研制的低温平面冷冻靶系统和低温红外光谱测量系统获得了低温下液氘的红外吸收谱.结果表明,实验测得的液氘红外吸收最强位置与理论计算得到的基态(D2)3分子的红外强度最大位置基本一致,且均为低模式Q1(0)+S0(0).     

On the thermal decomposition of the C60D19 deuterium fullerite

The gas-phase products of thermal decomposition of the C₆₀D₁₉ deuterium fullerite are studied by mass spectrometry. It is found that, in addition to D₂ molecules, the gas phase over the deuterium fullerite sample heated to a temperature of 773 K contains CD₄ methane and C₆D₆ benzene molecules. The deuterocarbon molecules are revealed in the gas phase even at 673 K.     

Synthesis of deuterium-labelled fluorobenzoic acids to be used as internal standards in isotope dilution mass spectrometry

A method for the deuterium labelling of fluorobenzoic acids (FBAs) via acidic H/D exchange of the aromatic hydrogen atoms in concentrated D₂SO₄ is described. The synthesis is shown to be easy, fast, low-priced and without the use of catalysts or further purification. The use of at least double-deuterated FBAs as internal standards in organic isotope dilution mass spectrometry allows the determination of FBAs in complex matrices with highest possible accuracy in combination with a simplified analytical evaluation.     

Adsorption of acetylene and ethylene on a clean Ir(111) surface

The adsorption of C₂H₂ and C₂H₄ on Ir(111) is studied within the temperature range 180–500 K by the HREELS and XPS methods. The absolute concentration of hydrocarbon coverage is estimated by XPS. Data are obtained on the kinetics of adsorption of the two gases at different temperatures. It is established by HREELS studies that at 180 K C₂H₄ forms ethylidyne (CCH₃ whereas C₂H₂ is adsorbed as CCH and ethylidyne species. At 300 K both kinds of species are found on the Ir(111) surface after C₂H₂ or C₂H₄ exposures. The ethylidyne decomposes completely to CCH at 500 K, which can be accompanied by polymerization of adsorbed hydrocarbon species.     

Determination of the deuterium temperature profile in magnetic fusion plasmas

Summary A new experimental method for determining the radial deuterium temperature profileT _D(R) in axisymmetrical toroidal fusion plasmas is presented. The method is based on a generalized Abel inversion of neutron brightness data providing the radial neutron emissivity profile of the plasma. This profile, combined with information on the deuterium density profile, is used to determineT _D(R) under the assumption that the ion velocity distribution is Maxwellian. Results are presented here from the analysis of JET data. It is found that, for typical JET plasma conditions, the dominant source of uncertainty arises from the high plasma impurity level and the fact that it is poorly known; these problems can be expected to be remedied and neutron brightness measurements would be expected to be very effective (especially in high-density plasmas) as aT _D(R) diagnostics.     

Hydrogen isotope replacement reactions on rhenium

The existence of a mobile equilibrium at room temperature between part of the hydrogen adsorbed on rhenium and gaseous hydrogen is demonstrated by the easy exchange of isotopes between the adsorbed layer and the gas phase. The adsorbed gas is desorbed as a mixture of homonuclear molecules (of H₂ or D₂)and of the isotopically mixed species (HD). However, the replacement reactions are not symmetrical; there is a greater proportion of HD in the desorbed gas when deuterium is replaced by hydrogen than in the converse reaction. This kinetic isotope effect is attributed to differences between the zero-point energies of the various hydrogen containing species.Quantatitive agreement between the shapes of the experimentally observed desorption curves and calculated curves is obtained if the zero-point energy of the bond between a surface rhenium atom and deuterium is assigned the value 2.6 kcal mole^?1.     

Correlation between hydrogen/deuterium exchange and Amide I band intensity in hemoglobin aqueous solution under static or 50 Hz magnetic field

Samples of hemoglobin in deuterium oxide solution (D₂O) and in bidistilled H₂O water solution, both at the concentration of 100 mg/ml, were exposed to a static magnetic field at 100 mT; analogous samples were exposed to 50 Hz magnetic field at 1 mT. Fourier Transform Infrared (FTIR) Spectroscopy was used to analyze separately the response of the secondary structure of this protein (diluted in both aqueous solutions) to separated exposure to both magnetic fields. The most relevant result which was observed after exposures was the significant increasing in intensity of the Amide I band, which was already explained in previous studies assuming that proteins α-helix aligned along the direction of the applied magnetic field due to its large dipole moment. In particular, in this study it was shown that hydrogen/deuterium exchange induced a reduction of the increasing of Amide I vibration band. This result can be explained assuming that Amide hydrogens of hemoglobin exchange with solvent deuterium atoms, causing an increase in mass of the protein and a correlated increasing in inertia of the α-helix, reducing significantly the torque effect of the applied magnetic field.     

Structure investigations of ultraphosphate glasses with some water content

Phosphorus pentoxide (P₂O₅) is a good glass-forming oxide, but highly hygroscopic. Therefore, glasses of the binary phosphate systems have to be melted in a closed system. Glasses in the systems P₂O₅–H₂O and P₂O₅–D₂O (up to 15 mol% H₂O or D₂O) and glasses with low metal oxide content (up to 12 mol%) were melted. The water as well as the deuterium oxide (D₂O) clearly modifies the glass structure. They act very similar to the metal oxides.     

Thermal evolution of acetylene and ethylene on Pd(111)

The thermal evolution of acetylene and ethylene and their deuterated counterparts on a palladium (111) surface has been studied by high-resolution electron energy loss spectroscopy in the temperature range 150–500 K. Analysis of the vibrational spectra indicates that chemisorbed acetylene evolves at 300 K in the presence of surface hydrogen to mainly ethylidyne, CCH₃, and a small amount of residual acetylene. Spectra obtained with and without preadsorbed hydrogen provide evidence for a 〉C CH₂ intermediate in the reaction. Chemisorbed ethylene also evolves to ethylidyne after heating from 150 to 300 K but much of the ethylene desorbs. The high temperature (400–500 K) behavior of C₂H₂ and C₂H₄ involves formation of a CH species. Although a small amount of the CH species may be formed from the dehydrogenation of ethylidyne, it is found that carbon-carbon bond scission of acetylene near 400 K is the dominant mechanism in CH formation.