Photoionization mass spectrometry studies of deuterated acetaldehydes CH3CDO and CD3CHO

Investigations of the fragmentation processes of acetaldehyde were performed by photoionization mass spectrometry of its deuterium labeled species CH₃CDO and CD₃CHO. Intramolecular exchange of hydrogen atoms (hydrogen scrambling) was observed. Obviously this process is accompanied by predissociation of the parent ion. Results are compared with previous work on acetaldehyde CH₃CHO.     

Quasiclassical Trajectory Study of the Reaction of CD4 with O(1D)

Extensive quasiclassical trajectory calculations for the O(¹D)+CD₄ multichannel reaction were carried out on a new global potential energy surface fit by permutationally invariant polynomials. The product branching ratios, translational energy distributions, and angular distributions of OD+CD₃, D+CD₂OD/CD₃O, and D₂+DCOD/D₂CO product channels were calculated and compared with the available experimental results. Good agreement between theory and experiment has been achieved, indicating small isotope effects for the title reaction. The O(¹D)+CD₄ reaction mainly proceeds through the CD₃OD intermediate via the trapped abstraction mechanism, with initial abstraction of the D atom rather than the direct insertion, followed by decomposition of CD₃OD into various products.     

Crossed Molecular Beam Study of H+CH4 and H+CD4 Reactions: Vibrationally Excited CH3/CD3 Product Channels

We study the H+CH₄/CD₄→H₂/HD+CH₃/CD₃ reactions using the time sliced velocity map ion imaging technique. Ion images of the CH₃/CD₃ products were measured by the (2+1) resonance enhanced multi-photon ionization (REMPI) detection method. Besides the CH₃/CD₃ products in the ground state, ion images of the vibrationally excited CH₃/CD₃ products were also observed at two collision energies of 0.72 and 1.06 eV. It is shown that the angular distribution of the products CH₃/CD₃ in vibrationally excited states gradually vary from backward scattering to sideways scattering as the collision energy increases. Compared to the CH₃/CD₃ products in the ground state, the CH₃/CD₃ products in vibrationally excited states tend to be more sideways scattered, indicating that larger impact parameters play a more important role in the vibrationally excited product channels.     

Hydrogen/deuterium abstraction by chlorine atoms from gaseous ethyl chlorides. Secondary kinetic isotope effects in the system CH3CH2Cl,CH3CHDCl,CH3CD2Cl

The abstraction of hydrogen/deuterium from CH₃CH₂Cl, CH₃CHDCl, and CH₃CD₂Cl by photochemically generated ground-state chlorine atoms has been investigated over the temperature range of 8–94°C using methane as a competitor. Rate constant data for the following reactions have been obtained: The temperature dependence of the relative rate constants k_i/k_j was found to conform to the Arrhenius rate law, where the stated error limits are one standard deviation: and k_r is the rate constant for the reference reaction (CH₄ + Cl → CH₃ + HCl). The β secondary kinetic isotope effects (k₂/k₃/k₄) are close to unity and show a slight inverse temperature dependence. Both preexponential factors and activation energies decrease as a result of deuterium substitution in the adjacent chloromethyl group. The trends are well outside the limits of experimental error.     

Vibrational spectra and rotational barriers of methyl titanium halides CH3TiX3 and CD3TiX3 (X = Cl,Br, I)

The IR and Raman spectra of gaseous and solid CH₃TiX₃ and CD₃TiX₃ species (X = Cl, Br, I) are reported. The gas phase spectra have been recorded between 4000 and 20 cm^?1 at pressures of 1 atm and 4 atm at 350 K and the Raman spectra of the solid phase recorded at 4.2 K. Internal rotation barriers and thermodynamic functions have been calculated.     

Microwave transitions of CD2=NCN

In continuation of our studies of the pyrolysis (1000°C) of (CH₃)₂NCN to alleged CH₂=NCN (I), N-cyanoformimine, (CD₃)₂NCN has been prepared and pyrolyzed (1000°C) to CD₂=NCN (II) as seen by its observed rotational transitions (18.6–40.0 GHz). The published rigid structural model of I and a corresponding structure of II are practically identical.     

Preparation and characterization of M(CH3)5 (M = Nb or Ta) and Ta(CH2C6H5)5 and evidence for decomposition by α-hydrogen atom abstraction

The preparations of Nb(CH₃)₅, Ta(CH₃)₅, and Ta(CH₂C₆H₅)₅ are reported in detail. The M(CH₃)₅ complexes decompose autocatalytically to give 3.4 ± 0.1 mol of methane and a non-hyclrolyzable residue with approximate composition MC_1–5H while Ta(CH₂C₆H₅)₅ decomposes in a non-autocatalytic manner to give ca. 2.6 mol of toluene per Ta. Decomposition of Nb(CD₃)₅ gave 96% CD₄ in diethyl ether while the toluene produced on decomposition of Ta(CD₂C₆H₅)₅ was at least 90%-d₃. An observed kinetic deuterium isotope effect of 2–3 in each case is evidence that an α-CH(D) bond is broken in a slow step of the decomposition. It is postulated that M(CH₃)₅ and Ta(CH₂C₆H₅)₅ decompose primarily by α-hydrogen atom abstraction though almost certainly in a complex, possibly intermolecular fashion in the case of M(CH₃)₅. In neither case (R = CH₃ or CH₂C₆H₅) was there evidence for significant homolytic cleavage of the metalcarbon bond to give free alkyl radicals.     

Deuterium kinetic isotope effect in the oxidation of sodium (2-D2)valerate with manganate in 3M aqueous NaOH solutions

Sodium (2-²H₂)valerate has been obtained by exchange technique and the kinetic parameters characterizing the oxidation of both sodium valerate of normal isotopic composition and sodium ,-dideuteriovalerate with manganate in 3M aqueous NaOH solutions have been determined. A discussion of the kinetic deuterium isotope effect observed in the oxidation of CH₃CH₂CH₂CD₂COONa is given.     

Comparative performance of CF3I,CD3I and CH3I in an atomic iodine photodissociation laser

We have compared the performance of CF₃I, CD₃I, and CH₃I in an atomic iodine photodissociation laser over the pressure range 1–200 torr. At pressures below 5 torr, CD₃I produces larger energy outputs, while above 5 torr CF₃I gives superior performance. The crossing of the laser energy output versus pressure curves is explained on the basis of collisional quenching of I(²P_{$\text{1}\text{2}$})(≡I^*) by undissociated alkyl iodide.     

Singlet methylene kinetics: Direct measurements of removal rates of ã1A1 and b̃1B1 CH2 and CD2

Rate constants for collisional removal of ã¹A₁ and b?¹B₁ CH₂ and CD₂ have been directly measured, using IR laser induced multiple photon dissociation to prepare the radicals, and time resolved laser induced fluorescence to observe them. For CH₂(ã¹A₁) removal by He, Ne, Ar, Kr, Xe, N₂, H₂, O₂, CO and CH₄, rate constants of 3.1, 4.2, 6.0, 7.0, 16, 8.8, 130, 30, 56 and 73 × 10^?12 cm³ molecule^?1 s^?1 were found respectively. These represent significant increases over the previously accepted values. Essentially no isotope effect is observed in the removal of CD₂(ã¹A₁) by the rare gases. The rate determining step in removal by the rare gases and N₂ is thought to be singlet—triplet intersystem crossing controlled by long range attractive forces, and the results are discussed in terms of both isolated and mixed state theoretical models of these processes. For the other molecular collision partners, bimolecular chemical removal channels are possible, and may account for the relatively fast rates observed. Radiative lifetimes of five Σ vibronic levels of CH₂(b?¹B₁) and three Σ vibronic levels of CD₂(b?¹B₁) have been measured and found to lie in the range 2.5–6.0 μs, and collisional quenching rates for CH₂(b?¹B₁) are found to be of the order of the gas kinetic collisional frequency.     

Magnetic order in AVX3 (A = Rb,Cs, (CD3)4 N; X = Cl,Br, I): A neutron diffraction study

AVX₃ (A = Rb, Cs, (CD₃)₄ N; X = Cl, Br, I) crystallize in the hexagonal system, space group $\text{P6}{}_3\text{mmc}$, with chains of face-sharing VX₆ octahedra along the c-axis. This leads to a pronounced one-dimensional character of their magnetic properties with a strong antiferromagnetic exchange interaction J between nearest neighbor V²⁺ ions along these chains. All compounds except [(CD₃)₄N]VCl₃ order three-dimensionally with ordering temperatures T_c between 13 and 32 K. In the ordered phase the magnetic moments, μ, lie in the basal plane in a triangular arrangement typical for antiferromagnetic interchain interaction J′.     

Reactions of free gold cluster cations with H2O, CH3Cl, and mixtures thereof

The reactions of the mass-selected gas-phase gold cluster cations Au₃⁺ and Au₅⁺ with H₂O, CH₃Cl, and mixtures of these reactants were studied under well-defined multi-collision conditions in an octopole ion trap. The reaction of CH₃Cl with the gold cations was found to proceed fast at room temperature, leading to the adsorption of one CH₃Cl molecule at each ‘corner’ atom of the cluster ion. This strong adsorption hindered the coadsorption of other reactants like H₂O. However, a considerable reduction of the CH₃Cl partial pressure led to distinct patterns of H₂O/CH₃Cl coadsorption products. Furthermore, the mass spectra indicated the loss of hydrogen after the reaction of CH₃Cl with Au₃⁺.     

1-Butyl-2,3-trimethyleneimidazolium bis(trifluoromethylsulfonyl)imide ([b-3C-im][NTf2]): a new, stable ionic liquid

Using imidazole as the starting material, the synthesis of a new bicyclic ionic liquid [b-3C-im][NTf₂] is described. Except for the alkylation reaction in the second step (40% yield) of this four-step synthesis of [b-3C-im][NTf₂], others were all high yielding reactions (85-94% isolated yields). We investigated intrinsic reactivity of this and other imidazolium-based ionic liquids and found that, under strongly basic conditions (KOD in CD₃OD/D₂O (1:1) solution), the new ionic liquid was stable to solvent deuterium isotope exchange while the previously reported [bdmim][NTf₂] and [bdmim][PF₆] ionic liquids were 50% deuterium exchanged at its C-2 methyl in 30 min at ambient temperature. At the same experimental condition, the most commonly employed [bmim][PF₆] ionic liquid was deuterium exchanged instantaneously at its C-2 hydrogen. In the absence of bases (CD₃OD/D₂O = 1:1), only [bmim][PF₆] was deuterium exchanged (50% within 1 h) and other ionic liquids gave no detectable exchanges even after one week at ambient temperature. It is therefore concluded that the new [b-3C-im][NTf₂] ionic liquid is far more chemically stable than previously reported [bmim][PF₆], [bdmim][NTf₂], and [bdmim][PF₆].     

Theoretical study of the structure and stability of the Na2Cl+, NaCl 2? , Na3Cl 2+ , and Na2Cl 3? ions

The geometrical parameters, normal vibration frequencies, and thermochemical characteristics of the Na₂Cl⁺, NaCl ₂ ⁻ , Na₃Cl ₂ ⁺ , and Na₂Cl ₃ ⁻ ions in saturated vapors over sodium chloride were calculated by the ab initio methods including electron correlation. According to calculations, the Na₂Cl⁺ and NaCl ₂ ⁻ triatomic ions have a linear equilibrium D _∞h configuration. The pentaatomic ions can exist in the form of the D _∞h linear isomer, C _2v planar cyclic isomer, or D _3h bipyramidal isomer. At ∼1000 K the Na₃Cl ₂ ⁺ and Na₂Cl ₃ ⁻ ions exist predominantly in the form of the linear isomers. The energies and enthalpies of the ion-molecule reactions involving the above ions were calculated. The formation enthalpy of the ions Δ_f H ⁰(0 K) was determined: 230 ± 2 kJ/mol (Na₂Cl⁺), −96 ± 4 kJ/mol (Na₂Cl ₃ ⁻ ), −616 ± 2 kJ/mol (NaCl ₂ ⁻ ), and −935 ± 4 kJ/mol (Na₂Cl ₃ ⁻ ). Original Russian Text Copyright ? 2007 by T. P. Pogrebnaya, A. M. Pogrebnoi, and L. S. Kudin __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 48, No. 6, pp. 1053–1061, November–December, 2007.     

Deuterium isotope effects and mechanism of the gas phase reaction [C3H7]+→[C3H5]+ + H2

The deuterium kinetic isotope effect and the deuterium isotope effect upon kinetic energy release have been calculated for the loss of H₂ from the [C₃H₇]⁺ ion. The calculations are based on the transition state structure suggested recently from ab initio calculations on the reaction pathway. The results obtained are in good agreement with experimental data.     

Neutron powder diffraction study of the layer organic-inorganic hybrid iron(II) methylphosphonate-hydrate, Fe[(CD3PO3)(D2O)]

The crystal and magnetic structures of the hybrid organic-inorganic layer compound Fe[(CD₃PO₃)(D₂O)] have been studied by neutron powder diffraction as a function of temperature down to 1.5 K. The neutron diffraction pattern recorded at 200 K shows that the fully deuterated compound crystallizes in one of the two known forms of the undeuterated Fe[(CH₃PO₃)(H₂O)]. The crystal structure is orthorhombic, space group Pmn2₁, with the following unit-cell parameters: a=5.7095(1) Å, b=8.8053(3) Å and c=4.7987(1) Å; Z=2. The crystal structure remains unchanged on cooling from 200 to 1.5 K. Moreover, at low temperature, Fe[(CD₃PO₃)(D₂O)] shows a commensurate magnetic structure (k=(0,0,0)). As revealed by bulk susceptibility measurements on Fe[(CH₃PO₃)(H₂O)], the magnetic structure corresponds to a canted antiferromagnet with a critical temperature T_N=25 K. Neutron powder diffraction reveals that below T_N=23.5 K the iron magnetic moments in Fe[(CD₃PO₃)(D₂O)] are antiferromagnetically coupled and oriented along the b-axis, perpendicular to the inorganic layers. No ferromagnetic component is observable in the neutron powder diffraction experiment, due to its too small value (<0.1μ_B).     

Deactivation of vibrationally excited CD3H using laser-induced fluorescence

Infrared fluorescence observed after exciting to ν₆ (ν=1) of CD₃H with a Q-switched CO₂ laser yields the exponential deactivation rate constant of 0.84 ms^?1 torr^?1. Rate constants for deactivation of CD₃H by rare gases vary from 1.4 (for He) to 0.029 (for Xe) ms^?1 torr^?1.     

Pb4Fe3O8Cl: Synthesis,crystal structure,and thermal expansion

Pb₄Fe₃O₈X (X = Cl and/or Br) was prepared by solid state reaction. The structure of Pb₄Fe₃O₈Cl was refined from X-ray single-crystal data in the centrosymmetric space group $\text{P4}\text{mmm}$ (a = 3.9097(2), c = 15.2873(17)); it can be described as an interlayering of incomplete perovskitelike sheets (Pb₄Fe₃O₈) with sheets of Cl. Fe(1) has a fivefold square pyramidal coordination while Fe(2) is in a regular octahedron of oxygen. Thermal expansion was measured from 25 to 500°C.