György Lendvay

POTENTIAL ENERGY SURFACE AND QUASICLASSICAL TRAJECTORY STUDIES OF THE N(2D)+H2 REACTION

We present a global potential energy surface for the 1A″ state of NH2 based on application of the reproducing kernel Hilbert space interpolation method to high quality ab initio (multireference configuration interaction) results. Extensive quasiclassical trajectory calculations are performed on this surface to study the N(2D)+H2/D2 reaction dynamics. Comparison is made with calculations on the lower level [first order configuration interaction (FOCI)] surface of Kobayashi, Takayanagi, Yokoyama, Sato, and Tsunashima (KTYST). We find a saddle point energy of 2.3 (1.9) kcal/mol for the perpendicular approach for the second order configuration interaction (SOCI) (SOCI with Davidson correction) surfaces, and a collinear stationary point energy of 5.5 (4.6) kcal/mol. The ordering of these stationary points is reversed compared to the corresponding FOCI results, and the only true reaction path on our surface is perpendicular. The primary reaction mechanism is determined to be C2v insertion to produce short lived...

Exploring the reaction dynamics of nitrogen atoms: A combined crossed beam and theoretical study of N(2D)+D2→ND+D

In the first successful reactive scattering study of nitrogen atoms, the angular and velocity distribution of the ND product from the reaction N(2D)+D2 at 5.1 and 3.8 kcal/mol collision energies has been obtained in a crossed molecular beam study with mass spectrometric detection. The center-of-mass product angular distribution is found to be nearly backward–forward symmetric, reflecting an insertion dynamics. About 30% of the total available energy goes into product translation. The experimental results were compared with those of quasiclassical trajectory calculations on an accurate potential energy surface obtained from large scale ab initio electronic structure computations. Good agreement was found between the experimental results and the theoretical predictions.

Formation of a2+ ions of protonated peptides. An ab initio study

The mechanism of the formation of a2+ ions from b2+ ions occurring during fragmentation of protonated peptides is investigated using quantum chemical methods. The geometries of the stationary structures involved in two possible mechanisms, namely, a two-step mechanism via an open-chain acylium ion and a concerted pathway involving rupture of two covalent bonds of the cyclic isomer of the b2+ ion, as well as the energetics of the reactions, were calculated at the MP2 and B3LYP levels, both combined with the 6-31G(d,p) as well as the 6-31++G(d,p) basis sets for the simplest analog of the b2+ ion. The energetically favored path is the direct expulsion of the CO molecule from the cyclic b2+ ion. The ZPE-corrected barrier height for this reaction is 26.2 kcal mol(-1) at the MP2/6-31G(d,p) level, while the highest barrier along the two step path is 31.4 kcal mol(-1). The barrier height for the reverse reaction is 3.8 kcal mol(-1), significantly smaller than the average kinetic energy release (KER) measured for larger b2+ ions. The barrier height for the reverse reactions of the MeCO-NH-CHMeCO+, NH2-iBuCH-CO-NH-CH2CO+, and NH2-CH2-CO-NH-CH(i-Bu)CO+ b2+ ions was found to be 11.3, 9.6, and 18.4 kcal mol(-1), in reasonable agreement with the measured KER for these reactions, indicating that the simplest model compound has unique properties in this respect. Based on comparisons with G2-MP2 calculations, comments are made on the applicability of various levels of theory for the description of the reaction.

Structure and bonding in binuclear metal carbonyls from the analysis of domain averaged Fermi holes. I. Fe2(CO)9 and Co2(CO)8

The nature of the bonding in the above carbonyls was studied using the analysis of domain averaged Fermi holes (DAFH). The results straightforwardly confirm the conclusions of earlier theoretical studies in which the existence of direct metal–metal bond, anticipated for the above carbonyls on the basis of 18‐electron rule, was questioned. In addition to indicating the lack of direct metal–metal bond, the DAFH analysis also allowed to characterize the nature of the electron pairs involved in the bonding of the bridging ligands. The analysis has shown that because the number of available electron pairs is not sufficient for the formation of ordinary localized 2c‐2e bonds between terminal M(CO)3 fragments and the bridging ligands, the bonding in both carbonyls exhibits typical features of electron deficiency and one bonding electron pair is effectively involved in multicenter 3c‐2e bonding. Because of the symmetry of the complexes the bridging ligands are not distinguishable and all M‐C‐M bridges have a partial 3c‐2e nature via resonance of the localized structures.

Theory of chemical reaction dynamics

Dedication to Evgueni Nikitin. Asymptotic interactions between open shell partners in low temperature complex formation: the H(X2S1/2)+O2(X3Epsilon=g) and O(3Pjsigma)+OH(X2Pi) systems A.I. Maergoiz, et al. Differential cross sections for abstraction reactions of halogen atoms with molecular hydrogen including nonadiabatic effects M.H. Alexander, Yi-Ren Tzeng. On the quantization of the electronic non-adiabatic coupling terms: the H+H2 system as a case study G. Halasz, et al. Non-adiabatic dynamics in the O+H2 reaction: a time-independent quantum mechanical study B. Maiti, G.C. Schatz. Nonadiabatic transitions between asymptotically degenerate states V.I. Osherov, et al. Coupling of electron momenta in ion-atom collisions B.M. Smirnov. Time-dependent wave packet calculations for reactive scattering and photodissociation G.G. Balint-Kurti, A. Brown. Quantum dynamics of insertion reactions P. Honvault, J.-M. Launay. Chebyshev propagation and applications to scattering problems Hua Guo. Molecular dynamics: energy selected bases J.C. Light, Hee-Seung Lee. Molecular reaction stereodynamics: in search of paths to overcome steric hindrances to reactivity V. Aquilanti, et al. The rotating bond umbrella model applied to atom-methane reactions G. Nyman. Reaction dynamics of polyatomic systems: from A + BCD --> AB + CD to X + YCZ3 --> XY + CZ3 Dong H. Zhang, Minghui Yang. Strong acceleration of chemical reactions arising through the effects of rotational excitation of reagents on collision geometry A. Miklavc. Dynamics studies of the O(3P) + CH4, C2H6 andC3H8 reactions D. Troya, G.C. Schatz. Dynamics of biomolecular reactions of vibrationally excited molecules E. Bene, et al. Towards a grid based universal molecular simulator A. Lagana. Vibrational predissociation: quasiclassical tunneling through classical chaotic sea E.E. Nikitin, J. Troe. Some recent advances in the modeling of ion-molecule association reactions J. Troe. Vibrational relaxation of diatoms in collisions with atoms at very low energies E.I. Dashevskaya, et al. Collisional energy transfer in the gas phase by classical trajectory calculations V. Bernstein, I. Oref. Manipulation of atoms and molecules with laser radiation and external fields M. Auzinsh. Photodissociation of hydrogen halides in a cryogenic rare gas environment: a complex approach to simulations of cluster experiments P. Slavicek, P. Jungwirth. List of participants of the Advanced Research Workshop. List of papers given at the Advanced Research Workshop. Index.

Quantum scattering studies of collisional energy transfer from highly excited molecules: Classical/quantum comparisons for collinear He+CS2

We present the results of an accurate quantum scattering study of collisional energy transfer in the collinear He+CS2 system, considering energies up to 75 kcal/mol. These results are generated using a coupled channel calculation, with vibrational eigenfunctions obtained from a discrete variable representation method. Detailed comparisons with the results of classical trajectory calculations are performed so as to assess classical/quantum correspondence for energy transfer moments, and for the energy transfer probability distribution function. We find very good agreement of the energy averaged first moments over a wide range of molecular vibrational energies provided that the translational energy is not too low (translational temperatures significantly below 300 K). The second moments, as well as 〈ΔE〉up and 〈ΔE〉down show less quantitative agreement, especially at low temperatures. The energy transfer distribution functions show considerable mode-specific behavior, but the overall envelope is approximately...

Electrochemical and quantum chemical studies on the formation of protective films by alkynols on iron

Abstract In order to find out the effect of cathodic and anodic polarisation on the formation of inhibitor films we measured the electrochemical impedance of an iron electrode in sulphuric acid and in hydrochloric acid solutions in the presence of oct-1-yn-3-ol or 2-〈2-(1,1-dimethyl-prop-2-ynyloxy)-ethoxy〉-ethanol inhibitors. We found that the anodic polarisation helped the initial binding of the inhibitor to the iron surface. Cathodic polarisation does not influence the initial formation but, if applied at a later stage, promotes the growth of the inhibitor film. The results support the assumption that film formation on iron surfaces from alkynols takes place in a two-step process: first chemisorption, then polymerisation. The binding of alkynols to iron was studied in model electronic structure calculations which indicate that a dative bond is formed between Fe and the triple bond. The calculated vibrational frequencies of the alkynol bound to iron can be used to successfully interpret the IR spectra found in the literature.

Air-stable, heme-like water-soluble iron(II) porphyrin: in situ preparation and characterization

Preparation of the water-soluble, kinetically labile, high-spin iron(II) tetrakis(4-sulfonatophenyl)porphyrin, Fe(II)TPPS4−, has been realized in neutral or weakly acidic solutions containing acetate buffer. The buffer played a double role in these systems: it was used for both adjusting pH and, via formation of an acetato complex, trapping trace amounts of iron(III) ions, which would convert the iron(II) porphyrins to the corresponding iron(III) species. Fe(II)TPPS4− proved to be stable in these solutions even after saturation with air or oxygen. In the absence of acetate ions, however, iron(II) ions play a catalytic role in the formation of iron(III) porphyrins. While the kinetically inert iron(III) porphyrin, Fe(III)TPPS3−, is a regular one with no emission and photoredox properties, the corresponding iron(II) porphyrin displays photoinduced features which are typical of sitting-atop complexes (redshifted Soret absorption and blueshifted emission and Q absorption bands, photoinduced porphyrin ligand-to-metal charge transfer, LMCT, reaction). In the photolysis of Fe(II)TPPS4− the LMCT process is followed by detachment of the reduced metal center and an irreversible ring-opening of the porphyrin ligand, resulting in the degradation of the complex. Possible oxygen-binding ability of Fe(II)TPPS4− (as a heme model) has been studied as well. Density functional theory calculations revealed that in solutions with high acetate concentration there is very little chance for iron(II) porpyrin to bind and release O2, deviating from heme in a hydrophobic microenvironment in hemoglobin. In the presence of an iron(III)-trapping additive that is much less strongly coordinated to the iron(II) center than the acetate ion, Fe(II)TPPS4− may function as a heme model.

On the dynamics of the O(1D) + CF3Br reaction

Abstract An experimental and theoretical investigation of the reactive properties of the O( 1 D) + CF 3 Br system has been carried out using crossed molecular beam scattering measurements and quasiclassical trajectory calculations. From the crossed beam experiment energy and angular distributions of the BrO reaction product were obtained. By carrying out trajectory calculations on a potential energy surface that we derived from spectroscopic and ab initio data, rate coefficients and scattering properties were estimated. The calculated properties are in reasonable agreement with experimental findings. Trajectory calculations were also performed to evaluate the temperature dependence of the rate coefficient of the processes leading to CF 3 O + Br and BrO + CF 3 .

Photocatalytic degradation of 1,5-naphthalenedisulfonate on colloidal titanium dioxide.

Photocatalytic degradation of 1,5-naphthalenedisulfonate (NDS) was investigated by monitoring the absorption and emission spectral changes, chemical oxygen demand, total organic carbon (TOC) content as well as pH and sulfate concentration. Intermediates formed during the irradiation were also detected by liquid chromatographic-mass spectrometric analysis. The results obtained by the applied analytical techniques clearly indicate that the initial step of degradation is oxygenation (hydroxylation) of the starting surfactant resulting in the formation of an 8-hydroxy derivative, although desulfonation and some mineralization, that is, decrease of TOC indicating carbon dioxide generation, also take place at this stage. Further oxygenation and desulfonation lead to the destruction of the diaromatic naphthalene system, then to ring fission, producing diols, aldehydes, and carboxylic acids on the side-chains. A tentative scheme involving possible pathways of degradation is proposed, taking the intermediates detected by mass spectrometry into consideration. On the basis of the results of quantum chemical calculations, the most possible points of attack by HO radical were identified, supplementing the MS results, and elucidating the initial oxidation step in the degradation of NDS and the benzenesulfonate (BS) intermediate. Thus, in the case of NDS para position is favored for hydroxylation, while for BS, formation of the ortho-hydroxy derivative is preferred.