Mechanistic and kinetic study the reaction of O(<Superscript>3</Superscript>P) + CH<Subscript>3</Subscript>CFCH<Subscript>2</Subscript>

The triplet potential energy surface of the O(³P) + CH₃CFCH₂ reaction has been investigated at the BMC-CCSD//MP2/6-311++G(d,p) level. Multichannel RRKM theory and transition state theory are employed to calculate the rate constants over a wide range of temperatures and pressures. The total rate constants show positive temperature dependence and pressure independence. At pressure of 10 Torr with He as bath gas, the addition/elimination on triplet potential energy surface is a dominant pathway. Major predicted end products are CH₃CFCHO (I) and H at the temperatures between 200 and 3,000 K; the direct hydrogen abstraction leading to OH + CH₂CFCH₂(I) plays an important role at higher temperatures. The calculated overall rate constants are in good agreement with the available experimental data.     

A full-dimensional time-dependent wave packet study of the OH + CO → H + CO<Subscript>2</Subscript> reaction

Full-dimensional time-dependent wave packet calculations were made to study the \(\hbox{OH}+\hbox{CO} \rightarrow \hbox{H}+\hbox{CO}_2\) reaction on the Lakin–Troya–Schatz–Harding potential energy surface. Because of the presence of deep wells supporting long-lived collision complex, one needs to propagate the wave packet up to 450,000 a.u. of time to fully converge the total reaction probabilities. Our calculation revealed that the CO bond was substantially excited vibrationally in the complex wells, making it necessary to include sufficient CO vibration basis functions to yield quantitatively accurate results for the reaction. We calculated the total reaction probabilities from the ground initial state and two vibrationally excited states for the total angular momentum J = 0. The total reaction probability for the ground initial state is quite small in magnitude with many narrow and overlapping resonances due to the small complex-formation reaction probability and small probability for complex decaying into product channel. Initial OH vibrational excitation considerably enhances the reactivity because it enhances the probability for complex decaying into product channel, while initial CO excitation has little effects on the reactivity. We also calculated the reaction probabilities for a number of J > 0 states by using the centrifugal sudden approximation. By doing some calculations with multiple K-blocks included, we found that the centrifugal sudden approximation can be employed to calculate the rate constant for the reaction rather accurately. The calculated rate constants only agree with experimental measurements qualitatively, suggesting more theoretical studies be carried out for this prototypical complex-formation four-atom reaction.     

Theoretical study on the ion–molecule reaction of HCN<Superscript>+</Superscript> with NH<Subscript>3</Subscript>

A detailed theoretical study is carried out at the B3LYP/6-311G(d,p) and CCSD(T)/6-311++G(3df,2pd) (single-point) levels as an attempt to investigate the mechanism of the little understand ion–molecule reaction between HCN⁺ and NH₃. Various possible reaction pathways are considered. It is shown that six dissociation products P ₁ (NH₃ ⁺ + HCN), P ₂ (NH₄ ⁺ + CN), P ₃ (NH₃ ⁺ + HNC), P ₉ (HCNH⁺ + NH₂) P ₁₀ (NCNH₃ ⁺ + H), and P ₁₂ (HNCNH₂ ⁺ + H) are both thermodynamically and kinetically feasible. Among these products, P ₁ is the most competitive product with predominant abundance. P ₃ and P ₉ may be the second feasible products with comparable yields. P ₁₂ may be the least possible product followed by the almost negligible P ₂ and P ₁₀ . Because the isomers and transition states involved in the HCN⁺ + NH₃ reaction all lie below the reactant, the title reaction is expected to be rapid, which is consistent with the measured large rate constant in experiment. The title reaction may have a potential relevance in Titan’s atmosphere, where the temperature is very low. Furthermore, our calculated results are compared with the previous experimental findings.     

A theoretical study on the dynamics of the gas phase reaction of NH<Subscript>2</Subscript>(<Superscript>2</Superscript>B<Subscript>1</Subscript>) with HO<Subscript>2</Subscript>(<Superscript>2</Superscript>A″)

Quasi-classical trajectory calculations and stochastic one-dimensional chemical master equation simulation methods are used to study the dynamics of the reaction of amidogen radical [NH₂(²B₁)] with hydroperoxyl radical [HO₂(²A″)] on the lowest singlet electronic state. The title complex reaction takes place on a multi-well multichannel potential energy surface consisting of three deep potential wells and one van der Waals complex. In quasi-classical trajectory calculations a new analytical potential energy surface based on CCSD(T)/aug-cc-pVTZ//MPW1K/6-31+G(d,p) ab initio method was driven and used to study the dynamics of the title reaction. In quasi-classical trajectory calculations, the reactive cross sections and reaction probabilities are determined for 200–2000 K relative translational energies to calculate the rate constants. The same ab initio method was used to have the necessary data for solving the one-dimensional chemical master equation to calculate the rate constants of different channels. In solving the master equation, the Lennard-Jones potential model was used to form the collision between the collider gases. The fractional populations of different intermediates and products in the early stages of the reaction were examined to determine the role of the energized intermediates and the van der Waals complex on the dynamics of the title reaction. Although the calculated total rate constants from both methods are in good agreement with the reported experimental values in the literature, the quasi-classical trajectory simulation predicts the formation of NH₂O + OH as the major channel in the title reaction in accordance with the previous studies (Sumathi and Peyerimhoff, Chem. Phys. Lett., 263:742–748, 1996), while the stochastic master equation simulation predicts the formation of HNO + H₂O as the major products.     

A study of the aerobic reaction between dopamine and Fe(III) in the presence of S<Subscript>2</Subscript>O<Subscript>3</Subscript><Superscript>2−</Superscript>

The reaction between Fe(III) and dopamine in aqueous solution in the presence of Na₂S₂O₃ was followed through UV–Vis spectroscopy, pH and oxy-reduction potential (Eh) measurements. The formation and quick disappearing of the complex [Fe(III)HL¹⁻]²⁺, HL¹⁻ = monoprotonated dopamine was observed with or without S₂O₃ ²⁻ at pH 3. An unexpected reaction occurs in presence of thiosulfate forming the stable anion complex [Fe(III)(L²⁻)₂]¹⁻, L²⁻ = dopacatecholate (λ = 580 nm) and the auto-increasing of the pH, from 3 to 7. It was proposed that H⁺ and molecular oxygen are consumed by free radical thiosulfate formed during the reaction.     

Wide-line <Superscript>1</Superscript>H NMR study of mesomorphic states of 4′-(octyloxy)-4-biphenylcarbonitrile

A sample of 4′-(octyloxy)-4-cyanobiphenyl (8OCB) was studied in the temperature range −60–80°C by wide-line ¹H NMR. The line shapes, half-widths, and second moments were determined. For the smectic phase of 8OCB, the relaxation times T ₁ and T ₂, the correlation time τ_c, and the degree of order were estimated. The ¹H NMR spectral patterns and characteristics were found to be quite different for the crystalline, smectic, and nematic phases of 8OCB, which makes it possible to reliably identify the corresponding transitions and assess the molecular dynamics and molecular order of a structure. The temperature ranges, stability conditions, and other characteristics of the liquid crystalline phases that form on heating 8OCB were determined.     

A study of the hydrolysis of ZrF<Stack><Subscript>6</Subscript><Superscript>2−</Superscript></Stack> and the structure of intermediate hydrolysis products by <Superscript>19</Superscript>F and <Superscript>91</Superscript>Zr NMR in the 9.4 T field

The high-field ¹⁹F and ⁹¹Zr NMR method is used to study the hydrolysis and polycondensation of hexafluorozirconate ZrF₆²⁻ in aqueous and water-peroxide solutions. During hydrolysis in aqueous solutions only ZrF₆²⁻ and F⁻ ions were observed by NMR, however, in the water-peroxide medium, an intermediate product of hydrolysis ([F₅Zr-OO-ZrF₅]⁴⁻ dimer) was detected. The dimer structure is confirmed by ¹⁹F and ⁹¹Zr NMR. In high fields (¹⁹F NMR frequency > 200 MHz), the fluorine exchange between ZrF₆²⁻ and F⁻ is slow in the ¹⁹F NMR scale and has a multisite character.     

Theoretical study on the mechanism of C2Cl3 + NO2 reaction

The radical-molecule reaction of C₂Cl₃ with NO₂ is explored at the B3LYP/6-311G(d,p) and CCSD(T)/6-311+G(d,p) (single-point) levels. On the singlet potential energy surface (PES), the association between C₂Cl₃ and NO₂ is found to be carbon-to-nitrogen attack forming the adduct C₂Cl₃NO₂ (1) without any encounter barrier, followed by isomerization to C₂Cl₃ONO (2). Starting from 2, the most feasible pathway is the N–O1 bond cleavage which lead to P ₁ (C₂Cl₃O + NO). Much less competitively, 2 transforms to the three-membered ring isomer c-OCCl₂C–ClNO (4 ^a ) which can easily interconvert to c-OCCl₂C–ClNO 4 ^b . Then 4 (4 ^a , 4 ^b ) takes direct C1–C2 and C2–O1 bonds cleavage to give P ₂ (COCl₂ + ClCNO). The lesser competitive channel is the 4 ^a isomerizes to the four-membered ring intermediate O-c-CNClOCCl₂ (5) followed by dissociation to P₃ (CO + ClNOCCl₂). The concerted 1,2-Cl shift along with C1–O1 bond rupture of 4 ^b to form ONC(O)CCl₃ (6) followed by dissociation to P ₄ (ClNO + OCCCl₂) is even much less feasible. Moreover, some of P ₃ and P ₄ can further dissociate to P ₅ (ClNO + CO + CCl₂). Compared with the singlet pathways, the triplet pathways may have less contribution to the title reaction. Our results are in marked difference from previous theoretical studies which showed that two initial adducts C₂Cl₃–NO₂ and C₂Cl₃–ONO are obtained. Moreover, in the present paper we focus our main attentions on the cyclic isomers in view of only the chain-like isomers are considered by previous studies. The present study may be helpful for understanding the halogenated vinyl chemistry.     

A simple and quick method for the preparation of radionuclide <Superscript>87</Superscript>Y/<Superscript>87m</Superscript>Sr generator using the <Superscript>nat</Superscript>Rb(α,xn)<Superscript>87</Superscript>Y reaction

A rapid method for the preparation of ⁸⁷Y/^87mSr radionuclide generator from a rubidium chloride target irradiated with 35 MeV α-particles is described. A simple two-step procedure is used to obtain a carrier-free ^87mSr isotope with a high enough radiochemical yield and high purity in the final aqueous fraction.     

The effect of NO<Stack><Subscript>3</Subscript><Superscript>−</Superscript></Stack> and OH<Superscript>−</Superscript> ions on the laser ablation of Cs<Superscript>+</Superscript> ion on Type 304 stainless steel

Type 304 stainless steel specimens artificially contaminated with CsCl solution were treated with KOH solution and KNO₃ solution, respectively. Cs⁺ ion removal tests by a Q-switched Nd:YAG laser at 1064 nm at a given fluence of 57.3 J/cm² were performed. The surface morphology and the relative atomic mole ratio of the specimen surface were investigated by SEM and EPMA. The order of Cs⁺ ion removal efficiency of laser was no-treatment < KOH < KNO₃ during the 42 shots. From the investigation of XPS peaks around 532.7 and 292.9 eV, KNO₃ on a surface of specimen was found to be fully decomposed during the laser irradiation. It was suggested that Cs₂O particulates formed by the reaction between the reactive oxygen generated from the nitrate ion and Cs⁺ ion on the metal surface could be easily suspended. For the KOH system, FeOOH was formed during the laser irradiation and it changed into Fe₂O₃. It was also suggested that Cs₂O particulates were formed by the reaction between the reactive oxygen generated from the decomposition of K₂O and Cs⁺ ion on the metal surface..     

Theoretical study of reaction mechanism for Se + O<Subscript>3</Subscript>

The reaction mechanism of Se + O₃ on the singlet potential energy has been investigated at CCSD(T)/6-311++G(2df,2pd) level of theory based on the geometric parameters optimized at the B3LYP/6-311++G(3df,3pd) level of theory. The calculated results show that the reactants are firstly associated into the adduct Se–O₃ with any intrinsic barrier. Subsequently, through a variety of transformations of isomer Se–O₃, two kinds of products P₁(SeO₃(D_3h)) and P₂(SeO + ³O₂) are obtained. The breakage and formation of the chemical bonds in the reaction have been studied by the topological analysis of electronic density. The topological analysis results show that the ring transitional structure region does not only occur in cis-OSeOO → SeO₃(C_s) process but also occur in SeO₃(C_s) → SeO₃(D_3h).     

A computational study of the radical–radical reaction of O(<Superscript>3</Superscript>P) + C<Subscript>2</Subscript>H<Subscript>5</Subscript> with comparisons to gas-phase kinetics and crossed-beam experiments

We present density functional theory (DFT) and complete basis set (CBS) calculations of the prototypical radical–radical reaction of ground–state atomic oxygen [O(³P)] with ethyl (C₂H₅) radicals. The respective reaction mechanisms and dynamics were investigated on the doublet potential energy surfaces using the DFT method and CBS model. In the title reaction, the barrierless addition of O(³P) to C₂H₅ led to the formation of energy-rich intermediates that underwent subsequent isomerization and decomposition to yield various products. The products predicted to be found were: H₂CO + CH₃, CH₃CHO + H, c–CH₂OCH₂ + H, ^1,3CH₃COH + H, ^1,3HCOH + CH₃, CH₂CHOH + H, C₂H₃ + H₂O, and CH₂CH₂ + OH. In particular, unlike previous kinetic results, proposed to proceed only through the direct H-atom abstraction process, two distinctive pathways to the formation of CH₂CH₂ + OH were predicted to be in competition: direct, barrierless H-atom abstraction mechanism versus addition process. The competition was consistent with the recent crossed-beam investigations, and their microscopic dynamic characteristics are discussed at the molecular level.     

Utilization of (p, 4n) reaction for <Superscript>86</Superscript>Zr production with medium energy protons and development of a <Superscript>86</Superscript>Zr → <Superscript>86</Superscript>Y radionuclide generator

Utilization of (p, 4n) reaction channel for the production of medical radionuclides became very attractive with commercial availability of medium energy cyclotrons. Significantly higher yields and radionuclidic purity may open new perspectives for several novel and some of the radionuclides previously have not been considered due to production difficulties. In present work, we show the proof-of-principle study on the production of ⁸⁶Y for Positron Emission Tomography imaging via radionuclide generator ⁸⁶Zr → ⁸⁶Y. Production suitability of ⁸⁶Zr from natural yttrium target and radiochemical separation strategies were tested. In addition, two generator systems were proposed and evaluated.     

<Superscript>13</Superscript>C-labeled bilirubin: synthesis of 3<Superscript>1</Superscript>(3<Superscript>2</Superscript>),17<Superscript>1</Superscript>(17<Superscript>2</Superscript>)-di-[<Superscript>13</Superscript>C]-mesobilirubin-XIIIα

Abstract  The title compound, labeled with ¹³C in the ethyl groups was synthesized from K¹³CN and low-molecular-weight components. The synthetic relay compound was 3¹(3²)[¹³C]-xanthobilirubinic acid methyl ester in a synthetic route that leads to a label in the ethyl β-substituent of a dipyrrinone model for bilirubin. This labeled dipyrrinone was oxidatively coupled to the dimethyl ester of mesobiliverdin-XIIIα, thereby providing a route to a ¹³C-labeled mesobiliverdin and mesobilirubin, with one carbon of each ethyl being 98% ¹³C-enriched. Graphical Abstract        

Theoretical study for the CH<Subscript>3</Subscript>OCF<Subscript>2</Subscript>CF<Subscript>2</Subscript>OCHO + Cl reaction

The reaction of CH₃OCF₂CF₂OCHO with Cl atom has been investigated theoretically by direct dynamics method. The BB1K hybrid functional in conjunction with the 6-31 + G(d,p) basis set has been used to optimize the geometries for the stationary points and explore the potential energy surface of the reaction. Four rotation conformers (RC1-4) of CH₃OCF₂CF₂OCHO are identified, and they are all considered in the kinetic calculation. For each conformer, there are two kinds of H-abstraction channels and one displacement channel, and the latter one should be negligible due to involving much higher energy barrier than the former two. The individual rate constants for each H-abstraction channel are evaluated by the improved canonical variational transition-state theory with a small-curvature tunneling correction. The overall rate constant is evaluated by the Boltzmann distribution function, and a fitted four-parameter rate constant expression is obtained over a wide temperature range of 200–2,000 K. The agreement between the calculated and available experimental value at 296 K is good. The contribution of each conformer to the title reaction is discussed with respect to the temperature. In addition, because of the lack of available experimental data for the species involved in the reactions, the enthalpies of the formation (ΔH _f,298°) for the reactant and its product radicals are predicted via isodesmic reaction at the BB1K/6-31 + G(d,p) level.     

Production possibility of <Superscript>186</Superscript>Re via the <Superscript>192</Superscript>Os(p,α3n)<Superscript>186</Superscript>Re nuclear reaction

Experimentally measured cross-sections are presented for the first time for the ¹⁹²Os(p,α3n)¹⁸⁶Re nuclear reaction up to 67 MeV. Highly enriched thin ¹⁹²Os targets (15 pcs), prepared by electro-deposition onto Cu backings, were irradiated with an external proton beam delivered by the SSC cyclotron of iThemba LABS. The excitation function curve of the ¹⁹²Os(p,α3n)¹⁸⁶Re reaction shows a maximum cross-section of ~82 mb at about 24 MeV. According to the yield calculations based on the present results, the available cumulative no-carrier-added ¹⁸⁶Re yield is 7.76 MBq/μAh (0.21 mCi/μAh) over the energy region 13.4 → 27.3 MeV.     

Theoretical evaluation of the radiative lifetimes of LiCs and NaCs in the A<Superscript>1</Superscript>Σ<Superscript>+</Superscript> state

Calculations of the adiabatic potential energy curves and the transition dipole moments between the ground (A¹Σ⁺) and the first excited (A¹Σ⁺) states have been determined for the LiCs and NaCs molecules. The calculations are performed using an ab initio approach based on non-empirical pseudopotentials for Cs⁺, Li⁺ and Na⁺ cores, parameterized l-dependent polarization potentials and full configuration interaction calculations. The potential energy curves and the transition dipole moment are used to estimate the radiative lifetimes of the vibrational levels of the A⁺Σ⁺ state using the Franck–Condon (FC) approximation and the approximate sum rule method. The radiative lifetimes associated with the A⁺Σ⁺ state are presented here for the first time. These data can help experimentalists to optimize photoassociative formation of ultracold molecules and their longevity in a trap or in an optical lattice.     

Comparison study of adsorption of Cl<Superscript>−</Superscript>, Br<Superscript>−</Superscript>, and I<Superscript>−</Superscript> ions from dimethyl formamide on In-Ga and Tl-Ga electrodes

The adsorption of Cl⁻, Br⁻, and I⁻ ions on the renewable liquid In-Ga and Tl-Ga electrodes from 0.1 M solutions in dimethyl formamide (DMF) is investigated by using the method of differential capacitance measurements. The results are compared with similar data obtained on Hg and Ga electrodes in DMF and with the corresponding data obtained in acetonitrile (AN). It is shown that, in DMF, the adsorption parameters and the series of surface activity of halide ions (Hal⁻) significantly depend on the metal nature. In contrast to Hg electrode, on which the surface activity of halide ions increases in the series: Cl⁻ < Br⁻ < I⁻, on In-Ga, as well as on the Ga electrode, it varies in the reverse order: I⁻ < Br⁻ < Cl⁻, whereas on the Tl-Ga electrode, partially reversed series of surface activity is observed: Br⁻ < I⁻ < Cl⁻. The results are explained within the framework of Andersen-Bockris model. An analysis of experimental results leads to the following qualitative conclusions: (1) on the In-Ga and Tl-Ga electrodes, as well as on Ga electrode, free energy of metal-Hal⁻ interaction ( $ \Delta G_{_{M - Hal^ - } } $ \Delta G_{_{M - Hal^ - } } ) increases in series I⁻ < Br⁻ < Cl⁻; (2) for Cl⁻, Br⁻, and I⁻, $ \Delta G_{_{M - Hal^ - } } $ \Delta G_{_{M - Hal^ - } } ) grows in series Tl-Ga < In-Ga < Ga; (3) an absolute magnitude of $ \Delta G_{_{M - Hal_1^ - } } - \Delta G_{_{M - Hal_2^ - } } $ \Delta G_{_{M - Hal_1^ - } } - \Delta G_{_{M - Hal_2^ - } } (Hal₁⁻, and Hal₂⁻ are any ions of Cl⁻, Br⁻, and I⁻) increases in series Hg < Tl-Ga < In-Ga < Ga; (4) the metal-DMF chemisorption interaction is much stronger than the metal-AN interaction and increases in series Tl-Ga < In-Ga < Ga.     

Quantum mechanical and molecular mechanics approach with a multilayered-quantum representation study of solvent effects and potentials of mean force for the CH<Subscript>3</Subscript>CH<Subscript>2</Subscript>Cl + ClO<Superscript>−</Superscript> S<Subscript>N</Subscript>2 reaction in aqueous solution

The bimolecular nucleophilic substitution reaction of CH₃CH₂Cl + ClO^? in aqueous solution was investigated using a multilayered-quantum representation, quantum mechanical and molecular mechanics approach with an explicit water model. Ten configurations along the reaction pathway including reactant complex, transition state and product complex were analyzed in the presence of the aqueous solution. The obtained free energy activation barrier under the CCSD(T)/MM representation is 13.2 kcal/mol, while it is 11.7 kcal/mol under the DFT/MM representation which agrees very well with the DFT calculation, at 11.0 kcal/mol, with a polarizable continuum solvent model. The solvent effects including the solvation free energy contribution and the polarization effect raise the free activation barrier by 9.8 kcal/mol. The rate constant, at 298 K, is 5.27 × 10^?17 cm³/molecule/s which is about seven orders of magnitude smaller than that in the gas phase (1.10 × 10^?10 cm³/molecule/s). All in all, the aqueous solution plays an essential role in shaping the reaction pathway for this reaction in water.     

Wide-line <Superscript>1</Superscript>H NMR study of 4′-(pentyloxy)-4-biphenylcarbonitrile in different phase states

A sample of 4′-(pentyloxy)-4-biphenylcarbonitrile was studied in the temperature range 20–70°C by wide-line ¹H NMR. The line shapes, half-widths, and second moments were determined. At 20°C, the spectrum is a broad structureless line, which was split into three components at temperatures above 47°C. This pattern persisted up to 65°C, with the components becoming narrower. Above 68°C, the spectrum rapidly collapses to give a structureless narrow line with a width δH < 0.01 G. Analysis of the spectra and comparison with theoretical calculations made it possible to elucidate the transition of the sample from the crystalline to the nematic and isotropic phases, as well as to determine the temperature range of the stability of the liquid-crystalline phase and the role of rotational mobility of protons of different functional groups and sometimes of these groups as a whole in the mechanisms of phase transitions.