Efficiency of shear surface wave transformation by the motion of the confining domain wall

The transformation of a shear surface magnetoelastic wave by the motion of the 180° confining domain wall in a ferromagnet is considered. Changes in the wave spectrum due to the motion of the wall are correlated with the variations of the energies of the elastic and magnetic subsystems. The efficiency of surface wave transformation by the domain wall motion is estimated in terms of energy. The frequency dependences of the mean energy density of the wave are found. It is shown that the energy density grows with wall velocity.     

Electron diffraction study of the molecular structure of gaseous 1,1-dibromo-3,3,5,5-tetramethyl-1-stanna-3,5-disila-4-oxacyclohexane,Br2Sn(CH2SiMe2)2O

The molecular structure of gaseous Br₂Sn(CH₂SiMe₂)₂O was studied by electron diffraction. The six-membered ring has a chair conformation whereas the entire molecule possessesC _s symmetry. The existence of a boat conformer cannot be completely excluded. The results of theoretical calculations for a twisted-boat conformation are at variance with the experimental data. Steric strain caused by mutual repulsion of the two axial methyl groups is reduced to the tilt of the Me₂Si fragments in opposite directions. This results in an increase (up to 26°C) in the angle formed by the bisector of the C_M-Si-C_M angle with the C_cSiO plane. The main geometrical parameters are as follows:r _g (Å): Si-O 1.708(20); Si-C_M 1.862(20); Si-C_c 1.882(9); Sn-C 2.108(26); Sn-Br 2.456(3); C-H 1.099(30); (degr.): C-Sn-C 105(2); Br-Sn-Br 107.9(1.2); Si-O-Si 129.6(3); C_M-Si-C_M 112; Si-C-H 113 (fixed value in accordance with experiment); C_c-Si-O 107(2); Sn-C-Si 109(2); torsion angles: (Si-C) 52(2); (Si-O) 62(1); (C_c-Sn) 54(1). The average amplitudes were fixed at the values calculated from the force field. Structural parameters of molecules with similar structures were analyzed and compared.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 384–387, February, 1993.     

Gas phase electron diffraction study of tetraphenyltin,Sn(C6H5)4

The geometrical parameters of the tetraphenyltin molecule have been determined by gas phase electron diffraction at about 310°. The S₄ and “open” D_2d molecular models with the tetrahedral bond configuration at tin were chosen for the structure analysis. The former gave the better fit. The thermal average bond lengths (r_g, in Å) are as follows:

The benzene ring geometry appears to be almost unaffected by bonding to tin. However, tin causes an increase in the endocyclic valence angle at the ipso-carbon atom to 121.0(0.9)° rather than a decrease of that angle as might be expected, tin being a σ-electron donor. The ring plane and the plane containing the

bond and S₄ axis make an angle, ?, of 34.1(2.1)°. The

bond length in tetraphenyltin is longer than not only the

bond in tetravinyltin (r_g = 2.117(4) Å) but also the

bond in tetramethyltin (r_g = 2.144(7) A).     

Molecular structures of acetylene derivatives of tin: Part IV. Gas-phase electron-diffraction study of tetraethynyltin,Sn(CCH)4, and triethynyltin iodide,ISn(CCH)3

The geometrical parameters of tetraethynyltin and triethynyltin iodide have been determined by gas-phase electron diffraction. Triethynyltin iodide was present as an admixture in both the tetraethynyltin samples studied. Because the samples differed significantly in percentage of the iodide (17.4 ± 4.0 and 47.1 ± 3.5 mol %, in samples A and B, respectively), it was possible to determine the structures of both molecules to a sufficient degree of accuracy.The r_α, structures were solved by the least-squares treatment of the molecular intensities, using mean amplitudes and shrinkage corrections calculated from the force fields of a number of tin derivatives.The T_d-symmetry model of Sn(CCH)₄ was refined to give the following parameters: Sn-C, 2.068(5); CC, 1.228(8); CH, 1.079(51). The structural parameters for ISn(CCH)₃ (on the basis of the C_3v model with linear Sn-CC-H fragments) are as follows: Sn-I, 2.646(4); Sn-C, 2.062(17); CC, 1.226(6); ∠ISnC 108.0(2.8). (The thermal average bond distances, r_g, are given in Å, and the valence angle, rα, in degrees; the values in paren- theses are three times the standard deviations, 3σ.)The Sn-C bonds in Sn(CCH)₄, and ISn(CCH)₃ are shorter than the corresponding bonds in the monoethynyltin derivatives, Me₃SnCCH and Me₃SnCCSnMe₃. The SnI bond in ISn(CCH)₃ is noticeably shorter than those in stannane iodide and trimethylstannane iodide.     

New approach to the nonparametric determination of the internal rotation potential from electron diffraction data. Reinvestigation ofm-bromonitrobenzene

A numerical algorithm for the nonparametric determination of the internal rotation potential from electron diffraction data using Tikhonov's regularization method is described. The range of admissible values of the regularization parameter is estimated using Hamilton's statistical criterion. m-Bromonitrobenzene was reinvestigated using this approach. It was found that the form of the potential may be reliably established only in the region of the minimum corresponding to the planar conformation of the molecule. Fourier series approximation of the experimental values of the potential in the region of the minimum gives the rotation barrier of 4.6–5.4 kcal/mole. The following basic geometrical parameters have been obtained (r_a in Å, ∠_α in deg, the error equals triple standard deviation): r(C?C)_ave=1.399(3), r(C?N)=1.459(16), 1.459(16), r(N=O)=1.244(3), r(C?Br)=1.884(6), r(C?H)=1.099(20), ∠CC_NC=123.9(1.4), ∠C_NCCBr=116.8(1.5), ∠C_NCC=116.6(1.9), ∠CNO=118.8(0.8). The results are compared with the data for the related compounds.     

The molecular geometries of some cyclic nitramines in the gas phase

The structural parameters of 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX), (CH₂NNO₂)₃, 1,3-dinitro-1,3-diazacyclopentane (DDCP), CH₂(CH₂NNO₂)₂, andN-nitropyrrolidine (NP), (CH₂)₄NNO₂, have been determined by electron diffraction.The six-membered ring of RDX has a chair form with axial positions of the nitro groups and close to planar bond geometry of the amine nitrogen atoms. The overallC ₃ symmetry of the molecule is in agreement with the experimental data.The conformation of the five-membered ring in DDCP is a half-chair ofC ₂ symmetry, while that in NP is an envelope ofC _S symmetry. The nitro groups are in equatorial positions in both molecules. The conformations of pyrrolidine and imidazolidine cycles show interesting features.The pyramidal geometry of the amine nitrogen atom bonds flattens in going from pyrrolidine andN-chloropyrrolidine to NP and DDCP and then to RDX and to dimethylnitramine (DMNA), (CH₃)₂NNO₂.     

Nonempirical quantum chemical calculation for nitramide,its chloro- and methyl-substituted derivatives. II. Structures and energies of transition states for internal rotation and inversion of the amino group

For five N-nitramines (H₂NNO₂, MeNHNO₂, ClNHNO₂, MeNClNO₂, Me₂NNO₂) using the program GAUSSIAN-90 we have carried out quantum chemical calculations by the restricted Hartree—Fock method, taking into account electron correlation by second-order Møller—Plesset perturbation theory in a standard 6–31G^* basis. In this paper, we consider the transition states for inversion of the amine nitrogen atom and rotation about the NN bond. We have obtained data on the changes in the geometric parameters during inversion and rotation. The changes in the NN bond length are especially significant they increase by 0.06–0.08 Å in the transition states for internal rotation compared with the equilibrium forms. We have calculated the barriers to inversion and internal rotation, the height of which strongly depends on the electronegativity of the substituents on the amine nitrogen atom. Estimates of the barriers to inversion lie within the range 0.4–6.0 kcal/mole while estimates of the barriers to rotation lie within the range 6–13 kcal/mole, which are 1.5–2 times lower than in amides and N-nitrosoamines.Moscow State University. Translated from Zhurnal Strukturnoi Khimii, Vol. 34, No. 1, pp. 12–19, January–February, 1993.     

Molecular Structure and Conformational Composition of 1-[(Methylthio)methyl]-2-nitrobenzene (MTMNB): A Theoretical and Experimental Study

The conformational composition of gaseous MTMNB and the molecular structures of the rotational forms have been studied by electron diffraction at 130^∘C aided by results from ab initio and density functional theory calculations. The conformational potential energy surface has been investigated by using the B3LYP/6-31G(d,p) method. As a result, six minimum-energy conformers have been identified. Geometries of all conformers were optimized using MP2/6-31G(d,p), B3LYP/6-31G(d,p), and B3LYP/cc-pVTZ methods. These calculations resulted in accurate geometries, relative energies, and harmonic vibrational frequencies for all conformers. The B3LYP/cc-pVTZ energies were then used to calculate the Boltzmann distribution of conformers. The best fit of the electron diffraction data to calculated values was obtained for the six conformer model, in agreement with the theoretical predictions. Average parameter values (r_a in angstroms, angle α in degrees, and estimated total errors given in parentheses) weighted for the mixture of six conformers are r(C–C) = 1.507(5), r(C–C)_{ring, av} = 1.397(3), r(C–S)_av = 1.814(4), r(C–N) = 1.495(4), r(N–O)_av = 1.223(3), ∠(C–C–C)_ring = 116.0–122.5, ∠ C6–C4–C7 = 118.2(4), ∠ C–C–S = 113.6(6), ∠ C–S–C = 98.5(12), ∠ N–C–C4 = 121.9(3), ∠(O–N–C)_av = 116.8(3), ∠ O–N–O = 127.0(4). Torsional angles could not be refined. Theoretical B3LYP/cc-pVTZ torsional angles for the rotation about C–N bond, φ_C−N, were found to be 30.5–36.5^∘ for different conformers. As to internal rotation about C–C and C–S bonds, values of φ_C−C = 68–118^∘ and φ_C−S = 66–71^∘ were obtained for the three most stable conformers with gauche orientation with respect to these bonds. Some conclusions of this work were presented in a short communication in Russ. J. Phys. Chem. 2005, 79, 1701.