A surface hopping quasiclassical trajectory study of the H2+ + H2 and (H2 + D2)+ systems

In this work we use a complete surface hopping quasiclassical trajectory method to determine cross sections for the reactions H₂⁺ + H₂ → H₃⁺ + H and the isotopic variants (H₂⁺ + D₂ and D₂⁺ + H₂). Initial translational energies ranged between 0.5 and 6 eV. The vibrational quantum number (v⁺) of the charged diatom is either 0 or 3. Comparing these results with our previous results with a partial treatment of surface hopping, we find essentially no change for v⁺ = 0 and reductions in cross sections of up to 30% for v⁺ = 3 trajectories.     

Excess molar volumes of (cyclohexanone+trichloromethane,or 1,2-dichloroethane,or trichloroethene,or 1,1,1-trichloroethane,or cyclohexane) at T=308.15 K,and of (cyclohexanone+dichloromethane) at T=303.15 K

Excess molar volumes V_m^E have been measured using a dilatometric technique for mixtures of cyclohexanone (C₆H₁₀O) with trichloromethane (CHCl₃), 1,2-dichloroethane (CH₂ClCH₂Cl), trichloroethene (CHClCCl₂), 1,1,1-trichloroethane (CCl₃CH₃), and cyclohexane (c-C₆H₁₂) at T=308.15 K, and for cyclohexanone+dichloromethane (CH₂Cl₂) at T=303.15 K. Throughout the entire range of the mole fraction χ of C₆H₁₀O, V_m^E has been found to be positive for χ C₆H₁₀O+(1−χ)c-C₆H₁₂, and negative for χ C₆H₁₀O+(1−χ)CH₂Cl₂, χ C₆H₁₀O+(1−χ)CHClCCl₂, χ C₆H₁₀O+(1−χ)CHCl₃, and χ C₆H₁₀O+(1−χ) CCl₃CH₃. For χ C₆H₁₀O+(1−χ)CH₂ClCH₂Cl, V_m^E has been found to be positive at lower values of χ and negative at high values of χ, with inversion of sign from positive to negative values of V_m^E for this system occurring at χ∼0.78. Values of V_m^E for the various systems have been fitted by the method of least squares with smoothing equation, and have been discussed from the viewpoint of the existence specific interactions between the components.     

Elucidating the structures of isomeric silylenium ions (SiC3H 9 + , SiC4H 11 + , SiC5H 13 + ) by using specific ion/molecule reactions

Specific ion/molecule reactions are demonstrated that distinguish the structures of the following isomeric organosilylenium ions: Si(CH₃) ₃ ⁺ and SiH(CH₃)(C₂H₅)⁺; Si(CH₃)₂(C₂H₅)⁺ and SiH(C₂H₅) ₂ ⁺ ; and Si(CH₃)₂(i?C₃H₇)⁺, Si(CH₃)₂(n?C₃H₇)⁺, Si(CH₃)(C₂H₅) ₂ ⁺ , and Si(CH₃)₃(π?C₂H₄)⁺. Both methanol and isotopically labeled ethene yield structure-specific reactions with these ions. Methanol reacts with alkylsilylenium ions by competitive elimination of a corresponding alkane or dehydrogenation and yields a methoxysilylenium ion. Isotopically labeled ethene reacts specifically with alkylsilylenium ions containing a two-carbon or larger alkyl substituent by displacement of the corresponding olefin and yields an ethylsilylenium ion. Methanol reactions were found to be efficient for all systems, whereas isotopically labeled ethene reaction efficiencies were quite variable, with dialkylsilylenium ions reacting rapidly and trialkylsilylenium ions reacting much more slowly. Mechanisms for these reactions and differences in the kinetics are discussed.     

A dynamic threshold in the F + H2 → HF + H reaction as determined from three-dimensional quasi-classical-reverse trajectory calculations

Quasi-classical dynamic threshold energies have been determined for two important reactive transitions in the F + H₂ reaction by performing extensive three-dimensional trajectory calculations for the corresponding reverse reactions. It is found that the energetic and dynamic thresholds for the reaction F + H₂(υ = 0,j) → HF(υ = 2,j = 6) + H are the same, whereas the latter threshold is approximately 0.08 eV greater than the former one for the reaction F + H₂(υ = 0,j) → HF(υ = 3,j=1) + H. These results are in good agreement with the corresponding semi-classical threshold results which are also reported. The relationship of these quasi-classical-reverse results to experimentally measured quantities is discussed.     

Thermodynamic study of systems with lower critical solution temperatures: H2O + (C2H5)3N,D2O + (C2H5)3N

Chand, A., McQuillan, A.R. and Fenby, D.V., 1979. Thermodynamic study of systems with lower critical solution temperatures: H₂O + (C₂H₅)₃N, D₂O + (C₂H₅)₃N. Fluid Phase Equilibria, 2: 263–274.Molar excess enthalpies and molar excess volumes are reported for the systems H₂O + (C₂H₅)₃N and D₂O + (C₂H₅)₃N at temperatures below and above their lower critical solution temperatures. The molar excess enthalpies are slightly less exothermic for the D₂O system. The molar excess volumes of the H₂O and D₂O systems are within experimental error of one another. Compositions of conjugate solutions estimated from the calorimetric and volumetric measurements agree with those obtained from published liquid—liquid phase diagrams.     

Densities and excess volumes of the ternary system butyl ethanoate + n-decane + 1-chlorobutane at 298.15 K

Excess molar volumes at 298.15 K and atmospheric pressure were measured for {x₁ CH₃CO₂(CH₂)₃CH₃ + x₂ C₁₀H₂₂ + (1 − x₁ − x₂) Cl(CH₂)₃CH₃} and the corresponding binary mixtures, with an Anton Paar densimeter. All the experimental values were compared with the results obtained by different prediction methods.     

Sigma-bond metathesis reactions of Sc(OCD3)2+ with water,ethanol, and 1-propanol: measurements of equilibrium constants,relative bond strengths,and absolute bond strengths

Fourier transform ion cyclotron resonance (FTICR) mass spectrometry has been used to examine the reactions of Sc(OCD₃)₂⁺ with water, ethanol, and 1-propanol. Sigma-bond metathesis resulting in the elimination of CD₃OH is the initial reaction observed, with further solvation of the metal center and subsequent elimination of hydrogen occurring as additional reaction channels. These processes are facile at room temperature and involve little or no activation energy. Measured equilibrium constants for the reaction Sc(OCD₃)₂⁺ +ROH ⇌ CD₃OScOR⁺ +CD₃OH with R =H, ethyl, and n-propyl are 0.013 ±0.004, 0.5 ±0.15, and 0.7 ±0.2, respectively. For the reaction ROScOCD₃⁺ +ROH ⇌ Sc(OR)₂⁺ +CD₃OH with R =H and ethyl the measured equilibrium constants are 0.013 ±0.004 and 0.3 ±0.1, respectively. ΔS is estimated for these processes using theoretical calculations and statistical thermodynamics, and in conjunction with the measured equilibrium constants we have evaluated ΔH for these reactions and the relative and absolute bond strengths of the Sc⁺–OR bonds, R =H, methyl, ethyl, and n-propyl. The relative bond strengths, D₂₉₈^o(CD₃OSc⁺–OR)–D₂₉₈^o(CD₃OSc⁺–OCD₃), for R =H, methyl, ethyl, and n-propyl are +11.9, 0, −0.1, and −1.4 kcal mol⁻¹, respectively. The absolute bond strengths for HOSc⁺–OCD₃, CD₃OSc⁺–OCD₃, CD₃OSc⁺–OC₂H₅, CD₃OSc⁺–OCH₂CH₂CH₃, and H₅C₂OSc⁺–OC₂H₅ are 115.0, 115.0, 114.9, 113.6, and 114.7 kcal mol⁻¹, respectively. Theoretical calculations with an LAV3P1 ECP basis set at the level of localized second-order Møller–Plesset perturbation theory were performed to evaluate ΔS and ΔG for the specific equilibria Sc(OH)₂⁺ +CD₃OH ⇌ CD₃OScOH +H₂O, CD₃OScOH +CD₃OH ⇌ Sc(OCD₃)₂⁺ +H₂O, and Sc(OCD₃)₂⁺ +C₂H₅OH ⇌ CD₃OScOC₂H₅⁺ +CD₃OH. The theoretically determined ΔG values agree reasonably well with the experimentally determined ΔG values. In accordance with earlier theoretical predictions, these metathesis reactions are consistent with an allowed four-center mechanism similar to that of a 2_σ +2_σ cycloaddition.     

Boiling Temperature and Reversed Deliquescence Relative Humidity Measurements for Mineral Assemblages in the NaCl + NaNO3 + KNO3 + Ca(NO3)2 + H2O System

Boiling temperature measurements have been made at ambient pressure for saturated ternary solutions of NaCl + KNO₃ + H₂O, NaNO₃ + KNO₃ + H₂O, and NaCl + Ca(NO₃)₂ + H₂O over the full composition range, along with those of the single salt systems. Boiling temperatures were also measured for the four component NaCl + NaNO₃ + KNO₃ + H₂O and five component NaCl + NaNO₃ + KNO₃ + Ca(NO₃)₂ + H₂O mixtures, where the solute mole fraction of Ca(NO₃)₂, x{Ca(NO₃)₂}, was varied between 0 and 0.25. The maximum boiling temperature found for the NaCl + KNO₃ + H₂O system is ≈134.9 ^∘C; for the NaNO₃ + KNO₃ + H₂O system is ≈165.1 ^∘C at x(NaNO₃) ≈ 0.46 and x(KNO₃) ≈ 0.54; and for the NaCl + Ca(NO₃)₂ + H₂O system is 164.7 ± 0.6 ^∘C at x{NaCl} ≈ 0.25 and x{Ca(NO₃)₂} ≈ 0.75. The NaCl + NaNO₃ + KNO₃ + Ca(NO₃)₂ + H₂O system forms molten salts below their maximum boiling temperatures and the temperatures corresponding to the cessation of boiling (dry-out temperatures) of these liquid mixtures were determined. These dry-out temperatures range from ≈300 ^∘C when x{Ca(NO₃)₂} = 0 to ≥ 400 ^∘C when x{Ca(NO₃)₂} = 0.20 and 0.25. Mutual deliquescence/efflorescence relative humidity (MDRH/MERH) measurements were also made for the NaNO₃ + KNO₃ and NaCl + NaNO₃ + KNO₃ salt mixture from 120 to 180 ^∘C at ambient pressure. The NaNO₃ + KNO₃ salt mixture has a MDRH of 26.4% at 120 ^∘C and 20.0% at 150 ^∘C. This salt mixture also absorbs water at 180 ^∘C, which is higher than expected from the boiling temperature experiments. The NaCl + NaNO₃ + KNO₃ salt mixture was found to have a MDRH of 25.9% at 120 ^∘C and 10.5% at 180 ^∘C. The investigated mixture compositions correspond to some of the major mineral assemblages that are predicted to control brine composition due to the deliquescence of salts formed in dust deposited on waste canisters in the proposed nuclear repository at Yucca Mountain, Nevada.     

Excess functions of (an alkane + carbon disulphide) at 298.15 K

Vapour pressures, excess enthalpies, and densities for {(1?x)C₆H₁₄ + xCS₂} {(1?x)C₁₀H₂₂ + xCS₂}, {(1?x)C₁₃H₂₈ + xCS₂}, and {(1?x)C₁₆H₃₄ + xCS₂} have been measured at 298.15 K. It was found that H_m^E and V_m^E increase as chain length increases while G_m^E diminishes, becoming negative for hexadecane.     

The Fe2+ chelate of hydrazinecarboxylic acid studied by the Mössbauer effect

The chelate compounds K[Fe(hyc)₃] and N₂H₅[Fe(hyc)₃]·H₂O (hyc = N₂H₃COO) were studied by the Mössbauer effect of ⁵⁷Fe at various temperatures. At room temperature the quadrupole splitting parameter is 2.77 mm/sec for K[Fe(hyc)₃] and 2.35 mm/sec for N₂H₅[Fe(hyc)₃]·H₂O, and the center shift is 1.08 mm/sec for both compounds. The temperature dependences of the quadrupole parameters yielded the crystal field splittings of the ⁵T_2g levels of the Fe²⁺ ions which indicate large trigonal distortion of the Fe(hyc)₃ anion. Using a molecular crystal-like treatment of the ferrous ion vibrations the temperature dependence of the recoilless fraction gave an effective Debye temperature Θ_D = 71°K for K[Fe(hyc)₃] and Θ_D = 90°K for N₂H₅[Fe(hyc)₃]·H₂O. No evidence for magnetic ordering was found down to 4.5°K in either compound.     

Solubility Determination,Hansen Solubility Parameters and Thermodynamic Evaluation of Thymoquinone in (Isopropanol + Water) Compositions

This article studies the solubility, Hansen solubility parameters (HSPs), and thermodynamic behavior of a naturally-derived bioactive thymoquinone (TQ) in different binary combinations of isopropanol (IPA) and water (H₂O). The mole fraction solubilities (x₃) of TQ in various (IPA + H₂O) compositions are measured at 298.2–318.2 K and 0.1 MPa. The HSPs of TQ, neat IPA, neat H₂O, and binary (IPA + H₂O) compositions free of TQ are also determined. The x₃ data of TQ are regressed by van’t Hoff, Apelblat, Yalkowsky–Roseman, Buchowski–Ksiazczak λh, Jouyban–Acree, and Jouyban–Acree–van’t Hoff models. The maximum and minimum x₃ values of TQ are recorded in neat IPA (7.63 × 10⁻² at 318.2 K) and neat H₂O (8.25 × 10⁻⁵ at 298.2 K), respectively. The solubility of TQ is recorded as increasing with the rise in temperature and IPA mass fraction in all (IPA + H₂O) mixtures, including pure IPA and pure H₂O. The HSP of TQ is similar to that of pure IPA, suggesting the great potential of IPA in TQ solubilization. The maximum molecular solute-solvent interactions are found in TQ-IPA compared to TQ-H₂O. A thermodynamic study indicates an endothermic and entropy-driven dissolution of TQ in all (IPA + H₂O) mixtures, including pure IPA and pure H₂O.     

Infrared chemiluminescence from the reactions F + HBr,F + H2Se,and Cl + H2Se

Infrared chemiluminescence from HF and HCl has been observed and yielded vibrational and rotational population distributions for the reactions F + HBr, F + H₂Se, and Cl + H₂Se. Evaluation of the spectra recorded by a commercial Fourier-transform spectrometer under low-flow conditions gave the following relative vibrational populations: for F ? HBr. N_{υ = 1} : N_{υ = 2} : N_{υ = 3} : N_{υ = 4} = 0.45 : 0.31 : 0.13 : 0.11: for F + H₂Se, N_{υ = 1} : N_{υ = 2} : N_{υ = 3} : N_{υ = 4} : N_{υ = 5} = 0.29 : 0.35 : 0.24 : 0.09 : 0.03: for Cl + H₂Se, N_{υ = 1} : N_{υ = 2} : N_{υ = 3} = 0.40 : 0.51 : 0.09. All three vibrational surprisal plots show a significant deviation from linearity. Neglecting the contributions from N_{υ = 0}, the total energy is partitioned into vibration and rotation as follows: 〈f_V〉 = 0.49 and 〈f_R〉 = 0.09 for F + HBr, 〈f_V〉 = 0.41 and 〈f_R〉 = 0.07 for F + H₂Se, 〈f_V〉 = 0.53 and 〈f_R〉 = 0.10 for Cl + H₂Se. Inclusion of estimates for N_{υ = 0} gives the more realistic values 〈f_V〉 = 0.24, 0.34, and 0.49 respectively. Whereas 9 ± 3% of the collisions between F + HBr yield Br in the excited ²P_{$\text{1}\text{2}$} state, no rovibrationally excited HSe fragments were detected in the two other systems. Consistent values for the bond dissociation energy D₀⁰(HSeH) = 329 ± 5 kJ/mol and the enthalpy of formation ΔH₁₀⁰ (HSe) = 137 ± 5 kJ/mol are derived from the highest observed HCl and HF levels.     

Excess enthalpy,excess heat capacity and excess volume of 1,2,4-trimethylbenzene +, and 1-methylnaphthalene + an n-alkane

A flow microcalorimeter of the Picker design was used to measure excess molar enthalpies H^E at 298.15 K as a function of mole fraction χ₁ for several mixtures belonging to series I: {χ₁1,2,4-C₆H₃(CH₃)₃ + χ₂n-C_ℓH_2ℓ+2}, and series II: {χ₁1-C₁₀H₇CH₃ + χ₂n-C_ℓH_2ℓ+2}. The chain length ℓ of the n-alkanes ranged between 7 and 16. 1,2,4-trimethylbenzene and 1-methylnaphthalene have about the same size and shape as the previously investigated chloro derivatives 1,2,4-C₆H₃Cl₃ and 1-C₁₀H₇Cl but a much smaller reduced dipole moment. The calorimeter was used in the discontinuous mode. A plot of H^E_max (i.e., the maximum value of H^E with respect to composition) against ℓ for series I shows a shallow minimum around ℓ = 11 with H^E_max (ℓ = 11) ≈ 250 J mol⁻¹, whereas H^E_max for series II decreases over the whole range 7 ⩽ ℓ ⩽ 16: H^E_max (ℓ = 7) ≈ 760 J mol⁻¹, and H^E_max (ℓ = 16) ≈ 595 J mol⁻¹. The corresponding enthalpic interaction parameters h₁₂, calculated from zeroth-order KGB (Kehiaian-Guggenheim-Barker) theory, decrease with increasing ℓ, and the rate of decrease, dh₁₂/dℓ, diminishes for larger chain lengths.For three mixtures belonging to series I (ℓ = 7, 10, 14), excess molar volumes V^E and excess molar heat capacities C^E_P at constant pressure were mesured at the same temperature. V^E was determined with a vibrating-tube densimeter (flow conditions), and C^E_P was obtained with another type of flow calorimeter (stepwise procedure). V^E(χ₁ = 0.5)/(cm³ mol⁻¹) = −0.207 for ℓ = 7, 0.060 for ℓ = 10, and 0.145 for ℓ = 14. The corresponding values for C^E_P x₁ = 0.5)/(J K⁻¹ mol⁻²) are 0.32, 0.66 and −0.09. Thus the chain length dependence of the excess molar heat capacity is qualitatively similar to that observed for the series with the homomorphic chloro derivative, (1,2,4-C₆H₃Cl₃ + n-C_ℓH_2ℓ+2), and to that of (1-C₁₀H₇Cl+n-C_ℓH_2ℓ+2).     

New aqua rhenium oxocomplex; synthesis,characterization, thermal studies,DFT calculations and catalytic oxidations

The aqua rhenium oxocomplex [ReO(OH)(H₂O)₄]^2? (1) has been prepared and characterized by spectroscopy, thermogravimetry, and elemental analysis and its reactivity towards triphenylphosphine has been evaluated. Complex (1) acts as a catalyst precursor in the presence of molecular oxygen for the oxidation of PPh₃ to OPPh₃. This proceeds through complex intermediates like [Re(PPh₃)_n]³⁺ (2), and [ReO(PPh₃)_n]³⁺ (3). The newly prepared complex (1) was also employed as catalyst for catalytic oxidation of cyclohexane. The geometry of [ReO(OH)(H₂O)₄]^2? has also been optimized in the singlet state by the DFT method with B3LYP level of theory.     

Excess molar enthalpies of triethylamine + ethylbenzene, + n-propylbenzene, + n-butylbenzene, + isopropylbenzene,and + isobutylbenzene at 303.15 K

Excess molar enthalpies H_m^E of triethylamine + ethylbenzene, + n-propylbenzene, + n-butylbenzene, + isopropylbenzene, and + isobutylbenzene were measured over the entire composition range at 303.15 K with an LKB flow microcalorimeter. H_m^E values are positive and decrease with increasing chain length of the alkylbenzene.     

Absorption and photoluminescence spectra of Tm3+-doped fluorophosphate glasses

We have carried out absorption and photoluminescence spectra of six newly prepared TmF₃ (2 M%) doped fluorophosphate glasses of composition: (NaPO₃)6BaF₂ZnF₂RF where R = Li, Na, K, (LiNa), (NaK) and (KLi). By evaluating the Judd—Ofelt intensity parameters for the measured absorption levels, the recorded photoluminescence spectra have been analysed to estimate the fluorescent radiative properties (A, A_T, β_R) and the stimulated emission cross-sections (σ^E_P) of the following luminescence transitions:¹G₄→³H₆ (λ=451 nm)¹D₂→³H₄ (λ=468 nm)³P₀→³F₂ (λ=482 nm)¹D₂→³H₅ (λ=492 nm)These have been determined in order to understand the alkali effects on the Tm³⁺-optical glasses studied.     

Resonance-enhanced multiphoton ionization of molecular hydrogen via the E,F1Σg+ state: Photoelectron energy and angular distributions

Photoelectron energy and angular distributions are measured for the 2+1 multiphoton ionization process H₂ X¹Σ_g⁺ (ν = 0,J) + 2hv → E,F¹Σ_g⁺(ν_E,J_E = J) + hν → H₂⁺X²Σ_g⁺ (ν⁺) + e^?, for ν_E = 0, 1, or 2 and for J_E = 0 or 1 of the inner well of the double-minimum E,F state. Although a strong preference is found for ν⁺ = ν_E, the detailed H₂⁺ vibrational distribution does not exhibit Franck-Condon behavior, and the photoelectron angular distributions vary markedly with both the J_E value of the intermediate state and the ν⁺ value of the ion.     

Interaction in the system Bi(NO3)3-K3HCit-(H2O + glycerol)

The interaction in the system Bi(NO₃)₃-K₃HCit-(H₂O + glycerol) was studied by chemical analysis and pH titration over a wide range of ratios between the initial components. Solid phases of the compositions Bi(OH)_3?3x HCit _x · nH₂O and KBiCit · H₂O were isolated and investigated by X-ray powder diffraction and differential thermal analyses and IR spectroscopy. The effect of the chemical nature of the alkali metal on the solubility in the system under consideration was demonstrated.