Structure characterization of molecular complexes for non-linear optical materials. II. 1 : 1 complexes of 4-methyl-morpholine-N-oxide (1) and 3-picoline-N-oxide (2) with 2,4,6-trinitrophenol, studied by X-ray, AM1 and DFT calculations

(1) C6H2N3O7- center dot C5H12NO2+, Mr = 346.26, P2(1)/c, a = 7.2356(6), b = 10.5765(9), c = 19.593(2) angstrom, 3 beta=95.101(6)degrees, V = 1493.5(2) angstrom(3), Z = 4, R-1 = 0.0414; (2) C6H2N3O7- center dot C6H8NO+, Mr = 38.24, P2(1)/n, a = 7.8713(5), b = 6.1979(7), c = 28.697(3) angstrom, beta = 90.028(7)degrees, V = 1400.0(2) angstrom(3), Z = 4, R-1 = 0.0416. The packing units in both compounds consist of hydrogen bonded cation-anion pairs. The (hyper)polarizabilities have been calculated for the crystallographic and optimized molecules, by AM1 and at the DFT/B3LYP(6-31G**) level.

Fully relativistic calculations on the potential energy surfaces of the lowest 23 states of molecular chlorine

The electronic structure and spectroscopic properties (R(e), omega(e), omega(e)x(e), beta(e), and T(e)) of the ground state and the 22 lowest excited states of chlorine molecule were studied within a four-component relativistic framework using the MOLFDIR program package. The potential energy curves of all possible 23 covalent states were calculated using relativistic complete open shell configuration interaction approach. In addition, four component multireference configuration interaction with single and double excitation calculations were performed in order to infer the effects due to dynamical correlation in vertical excitations. The calculated properties are in good agreement with the available experimental data.

Theoretical study of molecular and electronic structures of 5(1) knot systems: two-layered ONIOM calculations

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Investigation of the two-photon absorption cross-section in perylene tetracarboxylic derivatives: Nonlinear spectra and molecular structure

We investigated the 2PA absorption spectrum of a family of perylene tetracarboxylic derivatives ( PTCDs): bis( benzimidazo) perylene ( AzoPTCD), bis( benzimidazo) thioperylene ( Monothio BZP), n-pentylimidobenzimidazoperylene ( PazoPTCD), and bis( n-butylimido) perylene ( BuPTCD). These compounds present extremely high two-photon absorption, which makes them attractive for applications in photonics devices. The two-photon absorption cross-section spectra of perylene derivatives obtained via Z-scan technique were fitted by means of a sum-over-states ( SOS) model, which described with accuracy the different regions of the 2PA cross-section spectra. Frontier molecular orbital calculations show that all molecules present similar features, indicating that nonlinear optical properties in PTCDs are mainly determined by the central portion of the molecule, with minimal effect from the lateral side groups. In general, our results pointed out that the differences in the 2PA cross-sections among the compounds are mainly due to the nonlinearity resonance enhancement.

Molecular and morphological characterization of bis benzimidazo perylene films and surface-enhanced phenomena

Thin solid films of bis benzimidazo perylene (AzoPTCD) were fabricated using physical vapor deposition (PVD) technique. Thermal stability and integrity of the AzoPTCD PVD films during the fabrication (similar to 400 degrees C at 10(-6) Torr) were monitored by Raman scattering. Complementary thermogravimetric results showed that thermal degradation of AzoPTCD occurs at 675 degrees C. The growth of the PVD films was established through UV-vis absorption spectroscopy, and the surface morphology was surveyed by atomic force microscopy (AFM) as a function of the mass thickness. The AzoPTCD molecular organization in these PVD films was determined using the selection rules of infrared absorption spectroscopy (transmission and reflection-absorption modes). Despite the molecular packing, X-ray diffraction revealed that the PVD films are amorphous. Theoretical calculations (density functional theory, B3LYP) were used to assign the vibrational modes in the infrared and Raman spectra. Metallic nanostructures, able to sustain localized surface plasmons (LSP) were used to achieve surface-enhanced resonance Raman scattering (SERRS) and surface-enhanced fluorescence (SEF).

Theoretical study on the molecular mechanism for the reaction of VO2+ with C2H4

The complex reaction between VO2+ ((1)A(1)/(3)A) and C2H4 (Ag-1(g)/(3)A(1)) to yield VO+ ((1)Delta/(3)Sigma) and CH3CHO ('A'/(3)A) has been studied by means of B3LYP/6-31G* and B3LYP/6-311G(2d,p) calculations. The structures of all reactants, products, intermediates, and transition structures of this reaction have been optimized and characterized at the fundamental singlet and first excited triplet electronic states. Crossing points are localized, and possible spin inversion processes are discussed by means of the intrinsic reaction coordinate approach. Relevant stationary points along the most favorable reaction pathways have been studied at the CCSD/6-311G(2d,p)//B3LYP/6-311G(2d,p) calculation level. The theoretical results allow the development of thermodynamic and kinetic arguments about the reaction pathways of the title process. In the singlet state, the first step is the barrierless obtention of a reactant complex associated with the formation of a V-C bond, while in the triplet state a three-membered ring addition complex with the V bonded to the two C atoms is obtained. Similar behavior is found in the exit channels: the product complexes can be formed from isolated products without barriers. The reactant and product complexes are the most stable stationary points in the singlet and triplet electronic states. From the singlet state reactant complex, two reaction pathways are posssible to reach the triplet state product complex. (i) A mechanism in which a hydrogen transfer process is the first and rate limiting step and the second step is an oxygen transfer between vanadium and carbon atoms with a concomitant change in the spin state. The crossing point between singlet and triplet spin states is not kinetically relevant because it takes place at a later stage occurring in the exit channel. (ii) A mechanism in which the first stage renders a four-membered ring between vanadyl cation and the ethylene fragment and an oxygencarbon bond is formed; on going from this minimum to the second transition structure, associated with a carbon-vanadium bond breaking process, the crossing point between singlet and triplet spin states is reached. The final step is the hydrogen transfer between both carbon atoms to yield the product complex. In this case the spin change opens a lower barrier pathway. The transition structures with larger values of relative energies for both reactive channels of VO2+ ((1)A(1)) + C2H4 (Ag-1) --> VO+ ((3)Sigma) + CH3CHO ((1)A') present similar energies, and the two reaction pathways can be considered as competitive.

NH3+N2O3 reaction. High level calculations

We have undertaken a comprehensive study of the NH3 + N2O3 reaction in gas phase. Total energies of reactants, intermediates, transition states, and products have been calculated at CBS-QB3 level of theory. The corresponding BSSE analysis were performed at the highest level of theory, i.e. MP2 using the complete basis set (CBS) extrapolation at CBS-QB3 optimized geometries. A detailed mechanism was proposed for 2NH(3) - N2O3 -> 2N(2) - 3H(2)O with Delta H-r= - 170.08 kcal/mol N-2. (c) 2005 Elsevier B.V. All rights reserved.

Close-coupling calculations of positronium formation in positron-helium scattering

Positronium (Ps) formation in positron-helium scattering has been investigated in different partial waves at medium energies including the Ore gap region using the close-coupling approximation with realistic wavefunctions for the following states: He(1s1s), He(1s2s), He(1s2p), He(1s3s), He(1s3p), Ps(ls), Ps(2s), Ps(2p). Calculations are reported of rearrangement cross sections to Ps(ls), Ps(2s) and Ps(2p) states for incident positron energies up to 200 eV. The present partial cross sections are in good agreement with experimental results and a variational calculation in the Ore gap region.

Close-coupling calculations of elastic and inelastic positron-helium scattering

Elastic and inelastic positron-helium scattering have been investigated in different partial waves at medium energies using the close-coupling approximation with realistic wavefunctions employing the following states: He(1s1s), He(1s2s), He(1s2p), He(1s3s), He(1s3p), Ps(1s), Ps(2s) and Ps(2p). All excitations of the helium atom are in the spin-singlet electronic state. Calculations are reported of cross sections to He(1s1s), He(1s2s), and He(1s2p) transitions for incident positron energies up to 200 eV. These cross sections are in good agreement with experimental results.

The interaction between atoms of Au and Cu with clean Si(111) surface: A study combining synchrotron radiation grazing incidence X-ray fluorescence analysis and theoretical calculations

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Nonadiabatic calculations of the oscillator strengths for the helium atom in the hyperspherical adiabatic approach

Energies and wavefunctions are calculated for the bound states of the helium atom in the hyperspherical adiabatic approach by the full inclusion of nonadiabatic couplings. We show that the use of appropriate asymptotic radial boundary conditions not only allows the efficient calculation of energies accurate up to a few ppm for the ground state but also gives increasingly precise results for high-lying excited states with a unique set of equations. The accuracy of the wavefunctions is demonstrated by the calculation of oscillator strengths in the length form for transitions between stares ii S-1(e) and (n + 1) P-1(0) up to n = 29, in agreement with variational calculations.

Development of basis sets to calculations of the electronic structure of YMnO3

The generator coordinate Hartree-Fock method was used to develop 20s17p, 30s20p14d, and 30s21p16d Gaussian basis sets for the O ((3)p), Mn (S-6), and Y (D-2) atoms, respectively. The Gaussian basis sets were contracted to 20s17p/9s7p, 30s20p14d/11s7p7d, and 30s21p16d/14s7p7d and utilized in calculations of total energy and orbital energies of the (MnO1+)-Mn-5 and (YO1+)-Y-3 fragments to evaluate its quality in molecular studies. Finally, the contracted basis set for O atom was supplemented with one polarization function of d symmetry and used along with the other contracted basis sets (for Mn and Y) to calculate dipole moments, total energy, and total atomic charges in YMnO3 in space group D-6h. The analysis of those properties showed that is reasonable to believe that YMnO3 present behavior of piezoelectric material. (C) 2003 Elsevier B.V. All rights reserved.

Synthesis, X-ray Crystal Structure and Theoretical Calculations of Antileishmanial Neolignan Analogues

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Crystal, Molecular, and Electronic Structure of 1-Acetyl-indoline and Derivatives

The crystal and molecular structures of the following molecules have been determined: 1-acetyl-indoline, 1-acetyl-5-nitro-indoline, 1-acetyl-5-nitro-7-bromo-indoline, 1-acetyl-5-bromo-7-nitro-indoline, and 1-acetyl-5-bromo-7-nitro-indol. Molecular orbital calculations are performed for these compounds and two related species.

Role of the range of the dipole function in the classical dynamics of molecular dissociation

The dissociation dynamics of heteronuclear diatomic molecules induced by infrared laser pulses is investigated within the framework of the classical driven Morse oscillator. The interaction between the molecule and the laser field described in the dipole formulation is given by the product of a time-dependent external field with a position-dependent permanent dipole function. The effects of changing the spatial range of the dipole function in the classical dissociation dynamics of large ensembles of trajectories are studied. Numerical calculations have been performed for distinct amplitudes and carrier frequencies of the external pulses and also for ensembles with different initial energies. It is found that there exist a set of values of the dipole range for which the dissociation probability can be completely suppressed. The dependence of the dissociation on the dipole range is explained through the examination of the Fourier series coefficients of the dipole function in the angle variable of the free system. In particular, the suppression of dissociation corresponds to dipole ranges for which the Fourier coefficients associated with nonlinear resonances are null and the chaotic region in the phase space is reduced to thin layers. In this context, it is shown that the suppression of dissociation of heteronuclear molecules for certain frequencies of the external field is a consequence of the finite range of the corresponding permanent dipole. © 2013 American Physical Society.