Calculating Equilibrium Constants in the SnCl2–H2O–NaOH System According to Potentiometric Titration Data

Russian Journal of Physical Chemistry A - The potentiometric titration of tin chloride SnCl2 is performed in the concentration range of 0.00009–1.1 mol/L with a solution of sodium hydroxide...     

The Geometry, Vibrational Frequencies and Thermodynamic Properties of Naphthalene Based on ab initio Calculation

采用ａｂｉｎｉｔｉｏ方法，在ＨＦ／６３１Ｇ水平下计算了萘的几何构型和振动频率．计算所得几何构型和转动惯量与实验结果相符良好．计算所得振动频率平均比实验结果大９．５％左右；经校正（校正系数０．９０５）的计算频率与实验结果很接近．用校正后的频率计算所得不同温度下的热力学性质如标准熵、标准热容等与实验结果相吻合．     

An ab initio study of the E 3Πg state of the iodine molecule

The E (3)Π(g) state of the iodine molecule is studied by ab initio multireference methods coupled with effective core potentials and large basis sets. Two potential minima are found, a global featuring an ion-pair character, and a local presenting a purely Rydberg nature. Four avoided crossings along the dissociation coordinate attribute an interesting topology to its potential energy curve, and their effect on the vibrational levels of I(2) is discussed.     

Equilibria in a ZnCl2–H2O–NaOH System,According to Data from Potentiometric Titration,and Selecting Conditions for the Hydrochemical Synthesis of ZnS and ZnSe Films

Russian Journal of Physical Chemistry A - Equilibrium processes that occur in the ZnCl2–H2O–NaOH system are studied via the potentiometric titration of zinc chloride in the...     

Role of the 3(ππ*) state in photolysis of lumisantonin: insight from ab initio studies

The CASSCF and CASPT2 methodologies have been used to explore the potential energy surfaces of lumisantonin in the ground and low-lying triplet states along the photoisomerization pathways. Calculations indicate that the (1)(nπ*) state is the accessible low-lying singlet state with a notable oscillator strength under an excitation wavelength of 320 nm and that it can effectively decay to the (3)(ππ*) state through intersystem crossing in the region of minimum surface crossings with a notable spin-orbital coupling constant. The (3)(ππ*) state, derived from the promotion of an electron from the π-type orbital mixed with the σ orbital localized on the C-C bond in the three-membered alkyl ring to the π* orbital of conjugation carbon atoms, plays a critical role in C-C bond cleavage. Based on the different C-C bond rupture patterns, the reaction pathways can be divided into paths A and B. Photolysis along path A arising from C1-C5 bond rupture is favorable because of the dynamic and thermodynamic preferences on the triplet excited-state PES. Path B is derived from the cleavage of the C5-C6 bond, leading first to a relatively stable species, compared to intermediate A-INT formed on the ground state PES. Accordingly, path B is relatively facile for the pyrolytic reaction. The present results provide a basis to interpret the experimental observations.     

Fluorine spin–spin coupling constants of pentafluorobenzene revisited at the ab initio correlated levels

All possible spin–spin coupling constants, ¹⁹F–¹⁹F, ¹⁹F–¹³C, and ¹⁹F–¹H, of pentafluorobenzene were calculated at five different levels of theory, HF, DFT, SOPPA (CCSD), CCSD, and the SOPPA (CCSD)-based composite scheme with taking into account solvent, vibrational, relativistic, and correlation corrections. Most corrections were next to negligible for the long-range couplings but quite essential for the one-bond carbon–fluorine coupling constants. Hartree–Fock calculations were found to be entirely unreliable, while DFT results were comparable in accuracy with the data obtained using the wave function-based methods.     

An ab initio study of the rotation—vibration energy levels of GeH2 in the ā3B1 state

Thirty-five points on the potential energy surface of the ā³B₁ first excited state for the GeH₂ radical have been calculated using the (ab initio) MRD CI technique. Thirteen parameters in an analytic expression for the potential have been adjusted (by least-squares optimization) so that the surface fits these points. The rotation-vibration energy levels of GeH₂. GeD₂ and GeHD have been calculated using the non-rigid bender Hamiltonian, and we determine for GeH₂ that ν₁ = 1991 cm^-1. ν₂ = 763 cm^-1, and ν₃ = 2012 cm^-1. The equilibrium structure is found to be r_e = 1.545 Å and α_z = 119.8°, and the singlet-triplet splitting is calculated to be 22.8 kcal/mole (7975 cm^-1).     

Copper-Containing Catalysts Based on Cerium–Zirconium Oxide Supports in Ethanol Conversion Reaction According to In Situ IR Spectroscopic Data

Kinetics and Catalysis - Copper-containing catalysts based on CeO2–ZrO2 solid solutions were prepared by the Pecini method and studied using a set of physicochemical methods. It was found...     

Using ab initio “data” to accurately determine the fourth density virial coefficient of helium

We combine accurate ab initio calculations of the second and third density virial coefficients, B(T) and C(T), of ⁴He with measurements of its (p–ρ–T) behavior to determine the fourth density virial coefficient D(T). The measurements were made with a two-sinker, magnetic-suspension densimeter at pressures up to 38 MPa. The measurements on isotherms from T = 223 K to T = 323 K were previously published; new measurements from T = 323 K to T = 500 K are presented here. On each isotherm, a regression of the virial expansion was constrained to the ab initio values of B(T) and C(T); the regression determined D(T) as well as two apparatus-dependent parameters that compensated for systematic errors in the measurements. The percentage uncertainties of D(T) ranged from 2.6% at T = 223 K to 9.5% at T = 400 K to 24.7% at T = 500 K, where these uncertainties are expanded uncertainties with coverage factor of k = 2 corresponding to a 95% confidence interval. These uncertainties are 1/6th of the uncertainty obtained without the ab initio values of B(T) and C(T). The apparatus-dependent parameters can be used to calibrate the densimeter, and this will reduce the uncertainty of other measurements made with this two-sinker densimeter. The new values of D(T) will find applications in accurate gas metrology, such as a primary pressure standard based on the refractive index of helium.     

On the Calculation of Liquid–Vapor Interfacial Thickness Using Experimental Surface Tension Data

In this paper we investigate the vapor–liquid interfacial thickness of several pure fluids using a new method. In this method, the surface thickness is obtained using experimental surface tension data, and its dependence on the temperature is evaluated. The interfacial width is found to increase with increasing temperature and goes to infinity when the temperature approaches its critical value. Also, we find that a plot of ln δ versus ln {(1−T _r)⁻¹} is linear, in which δ and T _r are the interfacial thickness and reduced temperature, respectively. In this method, the equation of state obtained from the Statistical Associating Fluid Theory (SAFT EOS), which is molecular based, is accepted.     

Ab initio Calculation and Kinetic Study for the Abstraction Reaction of H with Sihcl3

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Quasirelativistic valence ab initio calculation of the potential-energy curves for Cd–rare gas atom pairs

The results of large-scale valence ab initio calculations of the potential-energy curves for the ground states and several excited states of Cd–rare gas (RG) van der Waals molecules are reported. In the calculations, Cd²⁰⁺ and RG⁸⁺ cores are simulated by energy-consistent pseudopotentials, which also account for scalar-relativistic effects and spin-orbit interaction within the valence shell. The potential energies of the Cd–RG species in the ΛS coupling scheme have been evaluated by means of ab initio complete-active-space multiconfiguration self-consistent-field (CASSCF)/CAS multireference second-order perturbation theory (CASPT2) calculations with a total 28 valence electrons, but the spin-orbit matrix has been computed in a reduced configuration interaction space restricted to the CASSCF level. Finally, the Ω potential curves are obtained by diagonalization of the modified spin-orbit matrix (its diagonal elements before diagonalization substituted by the corresponding CASPT2 eigenenergies). The calculated potential curves, especially the spectroscopic parameters derived for the ground states and several excited states of the Cd–RG species are presented and discussed in the context of available experimental data. The theoretical results exhibit very good agreement with experiment. Received: 20 April 2000 / Accepted: 1 September 2000 / Published online: 21 December 2000     

First Example of the Aza-Favorskii Reaction. Ethynylation of C=N Bond in the Superbasic System t-BuOK–DMSO

Russian Journal of Organic Chemistry - Direct ethynylation of ketimines with alkynes in the superbasic system t-BuOK–DMSO has been accomplished for the first time using the reaction of...     

The Na⋅⋅⋅B Bond in NaBH3−: A Different Type of Bond

A newly introduced Na−B bond in NaBH₃⁻ has been a challenge for the chemical bonding community. Here, a series of MBH₃⁻ (M=Li, Na, K) species and NaB(CN)₃⁻ are studied within the context of quantum chemical topology approaches. The analyses suggest that M–B interaction cannot be classified as an ordinary covalent, dative, or even simple ionic interaction. The interactions are controlled by coulombic forces between the metals and the substituents on boron, for example, H or CN, more than the direct M–B interaction. On the other hand, while the characteristics of the (3, −1) critical points of the bonds are comparable to weak hydrogen bonds, not covalent bonds, the metal and boron share a substantial sum of electrons. To the best of the author's knowledge, the characteristics of these bonds are unprecedented among known molecules. Considering all paradoxical properties of these bonds, they are herein described as ionic-enforced covalent bonds.     

Protonation Sites in Gaseous Pyrrole and Imidazole: A Neutralization–Reionization and ab initio Study

Mild gas-phase acids C₄H₉⁺ and NH₄⁺ protonate pyrrole at C-2 and C-3 but not at the nitrogen atom, as determined by deuterium labeling and neutralization–reionization mass spectrometry. Proton affinities in pyrrole are calculated by MP2/6–311G(2d, p) as 866, 845 and 786 kJ mol^-1 for protonation at C-2, C-3 and N, respectively. Vertical neutralization of protonated pyrrole generates bound radicals that in part dissociate by loss of hydrogen atoms. Unimolecular loss of hydrogen atom from C-2-and C-3-protonated pyrrole cations is preceded by proton migration in the ring. Protonation of gaseous imidazole is predicted to occur exclusively at the N-3 imine nitrogen to yield a stable aromatic cation. Proton affinities in imidazole are calculated as 941, 804, 791, 791 and 724 for the N-3, C-4, C-2, C-5 and N-1 positions, respectively. Radicals derived from protonated imidazole are only weakly bound. Vertical neutralization of N-3-protonated imidazole is accompanied by large Franck–Condon effects which deposit on average 183 kJ mol^-1 vibrational energy in the radicals formed. The radicals dissociate unimolecularly by loss of hydrogen atom, which involves both direct N-H bond cleavage and isomerization to the more stable C-2 H-isomer. Potential energy barriers to isomerizations and dissociations in protonated pyrrole and imidazole isomers and their radicals were investigated by ab initio calculations.