No abstract

No abstract

X-ray single-crystal study, molecular mechanics calculations, and calculations of the static nonlinear polarizabilities (β and γ) were performed for dicyanovinylbenzene and series of its mono- and dimethoxy-substituted derivatives. X-ray analysis has been done for dicyanovinylbenzene, its o- and p-methoxy- and 2,4-dimethoxy-substituted derivatives together with corresponding EFISH measurements of the β values for these compounds. Nonlinear polarizabilities were calculated for all series of the mono- and disubstituted methoxy derivatives of the parent compound with modified finite-field formalism that included calculation of polarization values versus static electric fields using semiempirical Hamiltonian, polynomial fit of all tensor elements of β and γ on the former data, and evaluation of the numerical instability of the calculations. All calculations were performed with optimized molecular geometries taken from X-ray data, molecular mechanics, ab initio, and semiempirical quantum chemical results. Good correlation was found between the predicted static and experimental molecular values of β. A factor of 2.0 was found to be a probable adjustment parameter to account for the solvent (1,4-dioxane) and dispersion (at 1064 nm) effects. Crystal packing analysis of the X-ray structures studied together with energetic calculations revealed the factors responsible for formation of centrosymmetric crystals. Only o-methoxydicyanovinylbenzene (also known as DIVA) forms acentric crystals (space group P21) among the experimentally studied compounds, and it was found that its molecular dipole moment orientation with respect to the polar crystal axis is close to the “optimal” for a manifestation of the high NLO responses.

The structural, electronic, and thermochemical properties of indium compounds which are of interest in halide transport and organometallic chemical vapor deposition processes have been studied by ab initio and statistical thermodynamic methods. The compounds reported include:  indium halides and hydrides (InF, InCl, InCl3, InH, InH2, InH3); indium clusters (In2, In3); methylindium, dimethylindium, and their hydrogen derivatives [In(CH3), In(CH3)H, In(CH3)H2, In(CH3)2, In(CH3)2H]; dimethylindium dimer [In2(CH3)4] and trimethylindium [In(CH3)3]; dehydrogenated methyl-, dimethyl-, and trimethylindium [In(CH3)2CH2, In(CH3)CH2, In(CH2)]; trimethylindium adducts with ammonia, trimethylamine and hydrazine [(CH3)3In:NH3, (CH3)3In:N(CH3)3, (CH3)3In:N(H2)N(H2)]; dimethylamino-indium and methylimino-indium [In(CH3)2(NH2), In(CH3)(NH)]; indium nitride and indium nitride dimer (InN, In2N2); indium phosphide, -arsenide, and -antimonide (InP, InAs, InSb). The predicted electronic properties are based on density functional theory calculations; the calculated thermodynamic properties are reported following the format of the JANAF (Joint Army, Navy, NASA, Air Force) Tables. Equilibrium compositions at two temperatures (298 and 1000K) have been analyzed for groups of competing simultaneous reactions.

A procedure for calculating homolytic dissociation rate constants is reported for modeling organometallic vapor-phase epitaxy (OMVPE) of III−V compounds for all pressure regimes. Reaction rate constants were predicted following a semiclassical approach based on quantum mechanical calculations and transition-state theory. The critical configuration was determined using linear interpolations for the geometry of the intermediate structures, Morse potentials for the intermediate electronic energies, and Hase's relationship for the vibrational frequencies that become annihilated. Low-pressure rate constants were calculated from Rice−Ramsperger−Kassel−Marcus (RRKM) theory following the Troe approach. The calculations were compared with experimental values for the dissociation of one methyl radical from the closed-shell molecules Al(CH3)3, Ga(CH3)3, and In(CH3)3 and the radical molecules Ga(CH3)2 and In(CH3) and for the dissociation of one hydrogen atom from NH3, PH3, and AsH3. A simplified system of reactions for the homolytic dissociation of In(CH3)3 was modeled in an OMV reactor designed for the pressure range 10-2 to 102 atm using computational fluid dynamics coupled with chemical kinetics. The steady-state simulations were carried out at 1000 K and at N2 pressures of 1 and 20 atm.

Valence electron contributions to the static molecular third-order polarizabilities (γ) are calculated for C 60 , C 70 , and two stable structures of C 84 (D 2 and D 2d ). The method utilized is based on the finite-field approach coupled with semiempirical polarization calculations on all-valence electrons. An increase in the third-order polarizability contributions is observed for molecular structures with a reduction in group symmetry, in agreement with recent experimental observations for these fullerenes. This increase is attributed mainly to the appearance of aromatic structures within the molecules as well as to the increase in molecular volume.Fullerenes are the subject of intensive research by many groups on several contents. There has also been a great deal of speculation about potential uses for fullerenes and their derivatives, ranging from electrochemistry and electronics (the latter based in part on the superconducting properties of alkalidoped fullerides) to catalysis, hydrogen storage, antiviral agents, and all-optical devices. 1 Associated with the delocalized π-conjugated electrons in fullerenes, their large nonlinear optical responses have been the subject of several recent experimental studies. 1-10 A wealth of experimental data concerning the thirdorder optical nonlinearities have been accumulated for the fullerenes C 60 , C 70 , and C 84 . The two most abundant fullerenes, C 60 and C 70 , have configurations with I h and D 5h symmetries, respectively. 11-14 C 84 has been recently synthesized, 15,16 and the most stable configurations have been determined to be D 2 and D 2d . 1,17 An interesting feature discovered by the experimental study is the increase of the third-order nonlinearity from C 60 to C 70 and to C 84 . 1 With the advances in the synthesis of macroscopic quantities of fullerenes, a theoretical understanding of the dependence of the nonlinear optical responses on the molecular symmetry and electronic properties is thus of particular interest.Theoretical calculations of third-order nonlinear effects have been carried out using various semiempirical and ab initio methods. π-electron calculations on unsaturated hydrocarbon chains have been used to predict third-order effects. 19 Ab initio methods applied to molecules with more than 15 atoms are extremely computer intensive. An alternative method using allvalence electrons and a semiempirical perturbation (sum-overstates approach) has generally been applied to molecules with less than 30 atoms. 20,21 In the present work, the procedure X

We have implemented a procedure to calculate static electronic molecular third-order polarizabilities for large molecules. The property is obtained semiempirically, using the finite-field formalism and either external or implicit fields, based on structures optimized by semiempirical, ab intio, or molecular mechanics methods. The numerical instability in the property is estimated, and various parameters can be modified to improve the uncertainty. The procedure involves first the calculation of the valence electron contribution to the property and then includes an estimate of the contribution from the electron cores.

No abstract