The internal rotation potential functions of the methacryloyl chloride molecule in the ground and excited electronic states

The systems of torsional vibration levels of the trans and cis methacryloyl chloride isomers in the ground (S ₀) and excited (S ₁) electronic states obtained by analyzing the vibrational structure of the gas-phase UV spectrum were used to reproduce the internal rotation potential functions of the molecule in both electronic states. The kinematic F factor in the S ₀ and S ₁ electronic states was calculated taking into account the relaxation of geometric parameters depending on the internal rotation angle. The internal rotation potential function parameters in the S ₀ state are substantially different from the parameters obtained using the torsional levels of the IR Fourier transform spectrum; at the same time, they are substantiated by quantum-mechanical calculations.     

Theoretical study of the structure of the CClF2NO and CCl2FNO molecules in the ground and lowest excited singlet and triplet electronic states

The potential energy surfaces of the nitroso compounds CClF₂NO and CCl₂FNO in the ground and lowest excited singlet and triplet electronic states were studied by various ab initio methods (including multiconfigurational methods). The equilibrium geometric parameters, vibrational frequencies, internal rotation potential functions, and rotational contours of bands in the S₁ S₀ vibronic spectrum of the CClF₂NO molecule were calculated. For the molecules under consideration, the quantum-mechanical problem on torsional motion was solved. The results of calculations are, on the whole, in good agreement with experiment.     

Investigations on adiabatic potential energy curve of Li2()

The SAC-CI method is used to investigate the spectroscopic properties of ⁷Li₂(). The adiabatic potential energy curves are calculated and fitted to the analytic Murrell–Sorbie function. The spectroscopic parameters reproduced by the potential attained at cc-PVTZ are found to be very close to the experiments. With the potential obtained at the SAC-CI/cc-PVTZ level of theory, a total of 62 vibrational states is found when J = 0. For each vibrational state, the vibrational level, classical turning points, inertial rotation and centrifugal distortion constants are calculated. Good agreement is obtained when they are compared with the available RKR data.     

Internal rotation potential functions of the acryloyl chloride molecule in the ground (<Emphasis Type="Italic">S</Emphasis><Subscript>0</Subscript>) and excited (<Emphasis Type="Italic">S</Emphasis><Subscript>1</Subscript>) electronic states

The internal rotation potential function of the acryloyl chloride molecule in the S ₀ and S ₁ electronic states was reproduced using systems of torsional vibration levels obtained for its trans and cis isomers by analyzing the vibrational structure of the UV spectrum of the molecule. The kinematic factor F in the S ₀ ground state was calculated including geometric parameter relaxation as a function of internal rotation angle. The torsional potential parameters in the S ₀ state obtained in this work were substantially different from those determined from the infrared Fourier-transform spectrum ignoring the resonance perturbation of the level with v = 3. The form of the internal rotation potential function and the higher stability of the trans isomer (the main isomer) were substantiated by high-level quantum-mechanical calculations.     

Electronic Energy Structure of a Series of Chalcopyrite-Like Compounds AgGaS2–CdGa2S4–InPS4

The effect of pseudovacancies on the density of electronic states of valence electrons in AgGaS₂, CdGa₂S₄, and InPS₄ is studied both experimentally, by means of X-ray spectroscopy, and theoretically, by calculating the partial densities of electronic states using the local coherent potential. The compounds under study are the derivatives of the sphalerite structural type (doubled cell) with gradually increasing deficiency of metals from to and further to , where is a vacancy. The environment of the metal atoms remains tetrahedral, while that of the sulfur atoms changes with increasing number of vacancies from four (AgGaS₂) to three (CdGa₂S₄) and two (InPS₄). For the compounds under study, SK and PK X-ray emission and absorption spectra were recorded at a resolution of about 0.2 eV, and the local partial densities of states were calculated for all components of the compounds. The theoretical curves practically coincide in shape and energy position of fine structure elements with the corresponding experimental curves. This allowed reliable conclusions about the energy positions of electronic states at the top of the valence band and about the dependence of the SK emission and absorption spectra in the series of compounds under study on variation of the crystal structure and on the chemical composition of the nearest surroundings of sulfur atoms.     

Potential function of the internal rotation of a methacrolein molecule in the ground (<Emphasis Type="Italic">S</Emphasis> <Subscript>0</Subscript>) electronic state

The structural parameters of s-trans- and s-cis-isomers of a methacrolein molecule in the ground (S₀) electronic state are determined by means of MP2 method with the cc-pVTZ basis set. Kinematic factor F(φ) is expanded in a Fourier series. The potential function of internal rotation (PFIR) of methacrolein in this state is built using experimental frequencies of transitions of the torsional vibration of both isomers, obtained from an analysis of the vibrational structure of the high-resolution UV spectrum with allowance for the geometry and difference between the energy (ΔH) of the isomers. It is shown that the V_n parameters of the potential function of internal rotation of the molecule, built using the frequencies of the transition of the torsional vibrations of s-trans- and s-cis-isomers of the methacrolein molecule, determined from vibrational structure of the high-resolution UV spectrum and the FTIR spectrum, are close.     

Trifluoroacetylation of divinyl sulfide

Conclusions The electrophilic attack of trifluoroacetic anhydride on divinyl sulfide results in replacing the-olefinic proton of only one double bond to give vinyl (2-trifluoroacetylvinyl) sulfide.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2402–2403, October, 1981.     

Structure and spectra of 1,3,2-dioxaphospholenes. 1. Microwave spectra of 2-chloro-4,5-dimethyl-1,3,2-dioxaphospholene and its isotopomers in the ground and excited vibrational states

The microwave spectrum of 2-chloro-4,5-dimethyl-1,3,2-dioxaphospholene (1) was studied in the frequency range from 7 to 53 GHz. Rotational transitions of the parent molecule in the ground and eleven excited vibrational states and those of its mono-substituted ³⁷Cl, ¹³C_Me, and ¹³C_Cycle isotopomers in the ground vibrational state were identified. Rotational constants and partial r _s-structure were obtained. The quartic centrifugal distortion constants, dipole moment components _a = 3.8D and _c = 0.24D (the total dipole moment is 3.81D), and the ³⁵Cl quadrupole coupling constants were determined for the parent molecule. The fine structure of the microwave transitions in the parent molecule was analyzed under the assumption of noninteracting methyl groups. The height of the barrier to internal rotation (V ₃₀ = V ₀₃ = 665 cm^–1) and the frequency of torsional vibrations ( = 167 cm^–1) were found. The frequencies of two lowest vibrational modes corresponding to deformation vibrations of the five-membered ring were estimated (100 cm^–1) from the relative intensities of rotational transitions for different vibrational states.     

An <Emphasis Type="Italic">ab initio </Emphasis> Quantum-Chemical Study of C<Subscript>6</Subscript>H<Subscript>5</Subscript>S(O)CH<Subscript>3</Subscript> and C<Subscript>6</Subscript>H<Subscript>5</Subscript>S(O)CF<Subscript>3</Subscript>

The potential functions of internal rotation around the C -S bond in the C₆H₅S(O)CH₃ and C₆H₅S(O)CF₃ molecules were obtained by ab initio MP2(full)/6-31+G* calculations. The stationary points were identified by solving the vibrational problems. The structures in which the plane of the C -S-C bonds is approximately perpendicular to the benzene ring plane correspond to the energy minimum. The barriers to rotation around the C -S bond, corrected for the zero-point vibration energy, are 21.29 [C₆H₅S(O)CH₃] and 28.98 [C₆H₅S(O)CF₃] kJ mol⁻¹. The bond angles (deg) are as follows: 95.7 (CSC), 107.1 (C SO), 106.3 (C SO) in C₆H₅S(O)CH₃; 93.5 (CSC), 108.2 (C SO), 105.2 (C SO) in C₆H₅S(O)CF₃. The bond lengths are as follows (Å): 1.520 (S=O), 1.804 (C -S), 1.810 (C -S) in C₆H₅S(O)CH₃; 1.507 (S=O), 1.799 (C -S), 1.870 (C -S) in C₆H₅S(O)CF₃. According to the results of NBO calculations, the formally double S=O bond consists of a strongly polarized covalent σ bond (S→O) and an almost ionic bond. An increase in the S=O bond multiplicity relative to a single bond is mainly due to hyperconjugation by the mechanism n(O)→σ*(C -S) and n(O)→σ*(C -S) and, to a lesser extent, by interaction of the oxygen lone electron pairs with the Rydberg orbitals of the S atoms, characterized by a large contribution of the d component.__________Translated from Zhurnal Obshchei Khimii, Vol. 75, No. 1, 2005, pp. 96–104.Original Russian Text Copyright © 2005 by Bzhezovskii, Il’chenko, Chura, Gorb, Yagupol’skii.     

A semiclassical adiabatic calculation of state densities for molecules exhibiting torsion: application to hydrogen peroxide and its isotopomers

A practical computational method is discussed for obtaining the rotational–vibrational molecular state densities of molecules with large amplitude torsional degrees of freedom (DoFs). This method goes beyond the traditional harmonic oscillator/rigid rotor or separable hindered rotor approximations in that it includes coupling between the torsion, the remaining vibrational modes, and the overall rotation. The method is based on the vibrationally adiabatic approximation whereby the torsional motion is assumed to be slow compared to the remaining vibrational DoFs although the nonseparability may be large. The torsional coordinate therefore parameterizes the rotational constants and the effective vibrational potential. A semiclassical method is then introduced to calculate the total state density in which the torsion is treated classically while the remaining coordinates are treated quantum mechanically. The method is also formulated for reactive problems in which the density of states is parameterized by a second large amplitude degree of freedom, the reaction coordinate. The performance of the method is assessed using the dissociation reaction of the hydrogen peroxide molecule and its isotopomers. It is found that the method performs well based on numerical tests. The torsional nonseparability is found to yield errors of factors of 2–3 in the statistical rate coefficient when compared with results of traditional separable models.     

Some analytical results forABC,ABCD, andXBCD coupled spin 1/2 systems. II

In the preceding paper, it was shown that the calculation of the density matrix(t) for multiply connectedABC, etc., spin 1/2 spin systems can be greatly simplified by subdividing the Hamiltonian into , where is a suitable linear combination of the constants of the motion. In this paper, a framework for the determination of the time evolution of high-order multipolar quantum states is presented and discussed. It is shown that the necessary mathematical labour is reduced to a minimum by (i) exploiting the fact that is a good quantum number, and (ii) using the theory of partitioned matrices. For example, it is shown that for a generaln-coupled spin 1/2 system, the spin dynamics of the multipolar states, whereK _max is the maximum tensorial rank, can be determined without the need to diagonalize the full 2 ⁿ × 2 ⁿ Hamiltonian matrix, wheren is the number of spins. In fact, to describe the time evolution of the multipolar states it is only necessary to diagonalize twon ×n matrices at most. Finally, some cautionary remarks are made concerning the use of the weak-coupling approximation.     

Hydrosilylation of diallyl and divinyl sulfides by dialkylfluorosilanes

Conclusions Hydrosilylation of diallyl sulfide with methylpropylfluorosilane (11 ratio) in the presence of H₂PtCl₆ forms a mixture of the- and -motioadducts in which the former predominates. The major pathway in the equivalent reaction of dialkylfluorosilanes with divinyl sulfide is addition by Farmer's rule. Diadducts are formed together with the monoadducts.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2548–2552, November, 1977.     

Theoretical conformational analysis of divinyl selenide

Theoretical conformational analysis of divinyl selenide was performed in terms of the Møller-Plesset second-order perturbation theory (MP2/6-311G**). Angular distribution of the probability density of populations of its rotational conformers was determined by analysis of the rotational potential energy surface. Divinyl sulfide was found to exist as an equilibrium mixture of three conformers having essentially nonplanar structure; the major conformer is syn-s-cis-s-trans, and the two others are syn- and anti-s-trans-s-trans with higher energy.     

Quantum-Chemical Study of Anisole Molecule

The potential functions of internal rotation around the C -O bond in the C₆H₅OCH₃ molecule were obtained by HF/6-31G(d), MP2(f)/6-31G(d), and B3LYP/6-31(d) calculations. Hartree-Fock calculations reveal a fourfold barrier to internal rotation around the C -O bond. The MP2 and B3LYP calculations reveal a twofold barrier with a height of 7.78 and 10.70 kJ mol^{- 1}, respectively (corrected for the zero vibration energy). The molecular geometries, first Koopmans ionization potentials, and dipole moments are reported. Calculations for liquid anisole in the self-consistent reactive field (SCRF) continual model give the results that only slightly differ from the results obtained for the isolated molecule in a vacuum. Within the framework of the Natural Bond Orbitals formalism, the following parameters were determined: energy, degree of hybridization, and population of oxygen lone electron pairs and energy of their interaction with antibonding ^* orbitals of the aromatic ring.     

Vibrational spectra,conformational stability,barriers to internal rotation,r0 structural parameters and ab initio calculations of fluoromethyl methyl ether

The far-infrared spectrum of gaseous fluoromethyl methyl ether, FCH₂OCH₃, along with three of the deuterium isotopes, has been recorded at a resolution of 0.10 cm^–1 in the 350 to 50 cm^–1 region. The fundamental asymmetric torsional and methyl torsional modes are extensively mixed and have been observed at 182 and 132 cm^–1, respectively, for the stablegauche conformer with the lower frequency band having several excited states falling to lower frequency. An estimate is given for the potential function governing the asymmetric rotation. On the basis of a one-dimensional model the barrier to internal rotation of the methyl moiety is determined to be 527±9 cm^–1 (1.51±0.03 kcal/mol). A complete assignment of the vibrational fundamentals for all four isotopic species observed from the infrared (3500 to 50 cm^–1) spectra of the gas and solid and from the Raman (3200 to 10 cm^–1) spectra of the gas, liquid, and solid is proposed. No evidence could be found in any of the spectra for the high-energytrans conformer. All of these data are compared to the corresponding quantities obtained from ab initio Hartree-Fock gradient calculations employing the 3-21G and 6-31G* basis sets along with the 6-31G* basis set with electron correlation at the MP2 level. Additionally, completer ₀ geometries have been determined from the previously reported microwave data and carbon-hydrogen distances determined from infrared studies. The heavy-atom structural parameters (distances in Å, angles in degrees) arer(C₁-F) = 1.395 ± 0.005;r(C₁-O) = 1.368 ± 0.007;r(C₂-O) = 1.426 ±0.003; FC₁O = 111.33 ± 0.25; C₁OC₂ = 113.50 ± 0.18 and dih FC₁OC₂ = 69.12 ± 0.26. All of these results are discussed and compared with the corresponding quantities obtained for some similar molecules.     

Calculation of low-lying electronic states of the MgN molecule in the effective-core-potential approximation

Plots of the potential energy and the dipole moment of four low-lying electronic states of the MgN molecule have been calculated by the self-consistent-field and configuration-interaction methods in the effective-core-potential approximation. The ground state of the molecule is not bound and has^4– symmetry. The lowest bound states,² and^2–, are practically degenerate; the values of the equilibrium internuclear distances (1.91 and 1.98 Å) and the vibrational constants (637 and 519 cm^–1, respectively) have been found for them. The vertical energy of the transition from these states to the ground state amounts to about 0.5 eV.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 21, No. 2, pp. 217–220, March–April, 1985.     

Intramolecular Nonbonded Interactions Between Oxygen and Group VIA Elements: An Ab Initio Molecular Orbital and Density Functional Theory Investigation of the Structures of HX—CH2—COOH (X=S,Se, and Te)

Ab initio molecular orbital and density functional methods have been used to study the potential energy surfaces of the substituted acetic acids HX—CH₂—COOH, where X is one of the Group VIA Chalcophiles S, Se, or Te. The various conformers adopted by these compounds provide information regarding the energetic importance of nonbonded and hydrogen bonding interactions involving oxygen atoms with different hybridizations. Density functional and ab initio molecular orbital methods yield similar structural and energetic trends for these compounds. Calculations show that the structure of the lowest-energy conformer of each of these acids has the X—C—C—O backbone substantially twisted from planarity, similar to that previously observed for the corresponding aldehydes, HX—CH₂—CHO. In the twisted acid structures the shortest distance is within about 0.1 Å of the sum of the X and O van der Waals radii, which reduces overcrowding of the lone pairs of electrons on these atoms. In conformers where the heavy atom backbone is planar, one of the distances is significantly shorter than the sum of the van der Waals radii, and the total molecular energy of these conformers is higher than that of the twisted forms. The variation of X—H vibrational frequencies among conformers reflects the extent of X—H hydrogen bonding, and indicates that formation of this hydrogen bond is not the dominant factor in determining the lowest-energy conformation. When X is oxygen (HO—CH₂—COOH), the lowest-energy conformer is also nonplanar, whereas for the corresponding aldehyde, HO—CH₂—CHO, the lowest-energy conformer is a planar structure with C_S symmetry. The conformational preferences of these simple species provide reference points for inter- and intramolecular interactions in more complex systems of biological interest.     

S1←S0 vibronic spectra and the vapor-state molecular structure of propanal and 2-methylpropanal

The vapor-state absorption spectra have been recorded for propanal PA and 2-methylpropanal MP with path lengths up to 120 m. The initial points in the S₁S₀ electronic transitions have been identified together with various fundamental vibrational frequencies of the PA and MP conformers. They contain nonplanar aldehyde groups in the S₁ states with inversion potential barriers of about 600 cm^–1. The parameters of the internal-rotation potential functions in the S₁ states have been determined, and the corresponding potential functions in the S₀ states have been refined.Chemical Faculty, Lomonosov Moscow University. Translated from Zhurnal Strukturnoi Khimii, Vol. 34, No. 1, pp. 20–25, January–February, 1993.     

Vibronic spectra,ab initio calculations,and structures of conformationally non-rigid molecules of oxalyl halides in the ground and lowest excited electronic states. Part V: Oxalyl chloridefluoride (COCl–COF)

The structure and conformational dynamics of the COCl–COF molecule in the ground and lowest excited electronic states were investigated theoretically by the CASPT2/cc-pVTZ method. The equilibrium geometric parameters, harmonic vibrational frequencies, potential functions of internal rotation, and adiabatic transition energies were obtained. According to the results of calculations, the molecule in the ground electronic state exist as the trans and gauche (dOCCO ~30–40°) conformers with a low potential barrier to gauche–gauche transition therefore it is impossible to exclude existence of the cis conformer (instead of gauche) with a very broad and flat potential minimum. For all the investigated excited electronic states of oxalyl chloridefluoride molecule calculations predicted the trans and cis conformers. The strong coupling of internal rotation around the C–C bond and non-planar vibrations of carbonyl fragments was found for the excited electronic states. The results of calculation were utilized for reanalysis of experimental \( \tilde{A}^{1} A^{\prime \prime} \leftarrow \tilde{X}^{1} A^{\prime} \) and \( \tilde{a}^{3} A^{\prime \prime} \leftarrow \tilde{X}^{1} A^{\prime} \) vibronic spectra reported in Kidd and King (J Mol Spectrosc 50:209–219 (1974), and ibid. 48:592–599 (1973)). The vibrational assignment that does not contradict the vibrational spectroscopy data and results of calculations was obtained.     

PMR investigation of internal inhibited rotation in N1,N1-dimethyl-N2-trifluoro[chloro]acetylamidines of picolinic and nicotinic acids

Summary Hindered rotation around the bond in the N-acylamidines has been investigated by PMR spectroscopy, and the kinetic parameters of the hindered rotation have been determined.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 758–762, April, 1981.