H+2 correlation diagram from finite element calculations

A two-dimensional, fully numerical approach to the electronic Schrödinger equation for linear molecules by the finite element technique is employed. For low-lying σ, π, δ and φ states of H⁺₂ and HeH²⁺ an accuracy of about 6 figures for the orbital energies with 211 grid points is found. Up to 10-figure accuracy is obtained with 496 grid points. An H⁺₂ correlation diagram, including states up to n = 5 of the united atom (He⁺), is given.     

Atomisation and chemical ionisation of Si,Ge and Sn in fuel-rich flames

The relationship between atomisation and ionisation for Si, Ge and Sn in fuel-rich C₂H₂ and H₂ flames has been studied by means of flame ionisation mass spectroscopy, thermochemical calculation of burnt gas equilibrium composition, and computer simulation of chemical ionisation kinetics. The mass spectra obtained from C₂H₂/Ar/O₂ flames are similar to those from H₂ diffusion flames: Sn yields Sn⁺ and SnOH⁺, Ge and Si yield GeOH⁺ and SIO⁺. These similarities are in contrast to the substantial differences in calculated atomisation found between the C₂H₂ and H₂ flames. The discrepancies between atomisation and ionisation are reconciled by a chemical ionisation mechanism in which the ions SiH⁺, GeH⁺ and SnH⁺ are important intermediates. The ratios of atomic ions to protonated monoxides, M⁺:MOH⁺ are determined by the thermochemistry for the reaction, MOH⁺ + H ⇌ M⁺ + H₂O.     

Theoretical study of structure and stability of h+x (h2)n clusters

The ion clusters H⁺X· (H₂)_n (X = N₂, CO, O₂ and H₂ andn = 0, 1, 2) are investigated by means of SCF and CI computations in a double-zeta plus polarization gaussian basis It is found that hydrogen molecules attack the proton of H⁺X perpendicularly. The calculated stabilization energies are in agreement with experimental values of δH⁰.     

Triquinoline- versus Fullerene-Based Cycloparaphenylene Ionic Complexes: Comparison of Photoinduced Charge-Shift Reactions

A triquinoline cationic moiety (TQ⋅H⁺) has recently been designed as a novel molecular unit for supramolecular chemistry. In addition to some useful features, TQ⋅H⁺ has strong electron-acceptor properties, which renders the molecular cation a unique element in nanochemistry. TQ⋅H⁺ is found to form complexes with coronene (COR) and cycloparaphenylene (CPP). In this work, we report a computational study of photoinduced electron transfer in supramolecular complexes TQ⋅H⁺-COR, TQ⋅H⁺⊂[12]CPP and (TQ⋅H⁺-COR)⊂[12]CPP. The electron-transfer rates are estimated by using the semi-classical approach. The results are compared with the data previously obtained for a structurally similar inclusion complex Li⁺@C₆₀⊂[10]CPP. In particular, we found a red solvatochromic shift for charge-shift bands in the TQ⋅H⁺-complexes unlike a blueshift showed by Li⁺@C₆₀⊂[10]CPP. This distinction is explored in terms of electronic and structural features of the systems.     

Collinear quantum mechanical calculations of the He + H+2 proton transfer reactions

Exact quantum mechanical results for collinear He + H⁺₂ → H + HeH⁺ reactive collisions are presented for the (total) energy range of 0.93 cV to 1.4 eV. The H⁺₂ initial vibrational states include ν = 0 through ν = 5. The diatomics-in-molecules semi-empirical surface of Kuntz is used in the computations. Except for a short range of energies, the calculated reaction probabilities of H⁺₂ (ν = 0) are larger than those of excited H⁺₂.     

Box orbitals for extended systems

A linear scaling of the number of nonzero integrals in extended systems calculations and the solution of the difficult cutoff threshold problems in the integral evaluation of periodic HF computations could be solved by the usage of orbitals with a finite extension. The present work proposes the usage of Box orbitals, defined inside spheres centered on the nuclei. Preliminary tests on small systems (atoms and H₂⁺) were performed. The results are very encouraging, since, in most cases, the Box orbitals give better results (giving results of equivalent quality in the worse cases) than do the classical Gaussian orbitals. No spurious effects were encountered. © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64 : 411–420, 1997     

Theoretical study of the reaction Ne + H+2 → NEH+ + H in the 2A′ ground state

A three-dimensional potential energy surface for the ²A′ ground state of the system (Ne? H₂)⁺ (²Σ⁺ in collinear geometry) has been calculated at SCF and CEPA levels. This surface describes the abstraction reaction which is endoergic by 0.57 eV (ΔH⁰₀) and has been studied recently by different experimental groups at low collision energies. Our CEPA calculations yield an endoergicity of 0.55 eV (ΔH⁰₀). The ²A′ surface has a minimum at collinear geometry with R_Ne—H = 2.29 a₀ and R_{H? H} = 2.08 a₀ and a well depth of 0.49 eV relative to Ne + H⁺₂. The effects of electron correlation on the shape of the surface and on the well depth are discussed. An analytic fit of the collinear part of the surface has been constructed based on Simon's proposal of using polynomials in the coordinates (R? R_e)/R instead of (R? R_e). The fitted potential is used for quantum mechanical scattering calculations with the finite element method (FEM ). Preliminary results for reaction probabilities for H⁺₂ in different vibrationally excited states are given and compared to the experimental results.     

pH-Metrische Studien an den binären Komplexen von Oxovanadium(IV) mit Hippur- und Anthranilsäure und Pyridin-2-aldoxim

pH-metric studies on the interaction of oxovanadium(IV) with hippuric and anthranilic acids and pyridine-2-aldoxime indicate the formation of monohydroxo derivatives of 1:1 chelates. The equilibrium constants for the reaction, VO²⁺+HA+H₂O?VO(OH)A+2H⁺ have been calculated as 4.47±0.07 and 6.32±0.05 in the 1:1 VO²⁺-hippuric or anthranilic acid systems resp. and for the reaction, VO²⁺+H₂ A ⁺+H₂O?VO(OH)A+3H⁺ as 8.40±0.09 in the 1:1 VO²⁺-pyridine-2-aldoxime hydrochloride system at 30±0.5°C (μ=0.1-KNO₃).     

SCF MO LCGO studies on the hydration of ions: The systems H+H2O,Li+H2O,and Na+H2O

The energy surfaces of the systems LiOH ₂ ⁺ and NaOH ₂ ⁺ are studied for a number of different geometries within the SCF MO LCAO framework, using a gaussian basis set to approximate the wavefunction. In the minimum energy geometry of both systems the positive ion is bound to the oxygen atom of the water molecule. The computed binding energies and bond distances are: B ^SCF(LiOH ₂ ⁺ ) = 36.0 kcal/mole, d(LiO) = 3.57 a.u., and B ^SCF(NaOH ₂ ⁺ ) = 25.2 kcal/mole, d(NaO) = 4.23 a.u., resp. The results are compared with those of H₃O⁺ and discussed in view of ion-solvent interaction in aquous solutions.It is a pleasure to thank our technical staff for the careful preparation of the input for the programs and for its enthusiastic and skilful assistance in running the computer.     

Propene adsorption and reaction on zeolites and pillared clays

Comparative IR and UV-Vis spectroscopic studies of propene adsorption and reaction on H-mordenite, dealuminated H-mordenite, dealuminated mazzite, montmorillonite and Al₁₃-pillared montmorillonite have been carried out. On all systems propene is first transformed into polymeric species (C_nH_2n+1 ⁺). On HMOR (both as such and dealuminated), allylic carbocations are successively produced by loss of H₂, the monoenic species (C_nH_2n?1 ⁺) being formed at room temperature and the dienic (C_nH_2n?3 ⁺) and trienic (C_nH_2n?5 ⁺) species at higher temperatures. These species are not observed on the other systems, although they are presumably formed as unstable intermediates. In fact, on all the zeolites studied here two cyclic penta-atomic and hexa-atomic allylic carbocations have been observed for the first time. On all systems, the final products of reaction are polyaromatic species which, on the basis of their reaction with NH₃ still exhibit unsaturated carbocation behaviour. The activity of the various samples depends on their pore dimensions and on the nature of acidic sites involved: the larger the available pore space, the more branched is the polymer and the more difficult it is to observe allylic carbocations. Evidence is provided for a Brønsted-induced mechanism.     

Variational calculation of vibrational energies of triatomic molecules using SCF optimized modes

A self-consistent field optimization of the vibrational coordinates for nonlinear triatomic molecules is presented. The optimal coordinates are obtained by making a three-dimensional rotational transformation of the normal modes and determining the rotation angles as those for which the SCF energy is stationary. The utility of the optimized coordinates in full variational calculations of vibrational energies is studied for the molecules of H₂O, O₃, H₂D⁺, H₂T⁺, and D₂T⁺. For H₂O and O₃, the optimization procedure leads to the local mode representation. It is shown that the use of the optimal coordinates in variational calculations allows a large reduction of the dimension of the Hamiltonian matrix to be diagonalized in order to reach convergence.     

On the affinity of cytosine towards electrophiles

Ab initio SCF computations on the intrinsic preferences of the H⁺, CH ₃ ⁺ and C₂H ₅ ⁺ cations towards the two principal sites of protonation or alkylation on cytosine, N₃ or O₂, show that this preference undergoes a continuous modification with the increase in size and complexity of the cation. N₃ is the preferred site of fixation of H⁺, O₂ the preferred site of C₂H ₅ ⁺ , while CH ₃ ⁺ has no marked preference. The exchange repulsion term of the binding energy appears responsible for the preference of C₂H ₅ ⁺ for O₂.This work was supported by the Ligue Francaise contre le Cancer and the National Foundation for Cancer Research (USA)     

Modeling the H5+ potential-energy surface: a first attempt

 Ab initio molecular electronic structure calculations are performed for H₅ ⁺ at the QCISD(T) level of theory, using a correlation-consistent quadruple-zeta basis set. Structures, vibrational frequencies and thermochemical properties are evaluated for ten stationary points of the H₅ ⁺ hypersurface and are compared with previous calculations. The features of the H₃ ⁺…H₂ interaction at intermediate and large intermolecular distances are also investigated. Furthermore, an analytical functional form for the potential-energy surface of H₅ ⁺ is derived using a first-order diatomics-in-molecule perturbation theory approach. Its topology is found to be qualitatively correct for the short-range interaction region. Received: 15 March 2001 / Accepted: 5 July 2001 / Published online: 11 October 2001     

AB initio calculations of the stability of the OH+4 and FH+3 ions

Some geometric configurations of the OH⁺₄ and FH⁺₃ ions have been calculated by the SCF MO LCAO method using linear combinations of gaussian lobe functions. The total electronic energies of the systems under study are lower than the sum of the energies for H₂O and H⁺₂ or OH⁺₃ and H, and HF and H⁺₂ or FH⁺₂ and H, respectively.     

Effect of method of ion preparation on low-energy collision-induced dissociation mass spectra

The collision-induced dissociation (CID) mass spectra of protonated cocaine and protonated heroin have been measured using a triple quadrupole mass spectrometer at 50 eV ion/neutral collision energy for protonated molecules prepared by different protonating agents. The CID mass spectra of protonated cocaine using H⁺(H₂O)_n, H⁺(NH₃)_n and H⁺((CH₃)₂NH)_n as protonating agents are essentially identical and it is concluded that, regardless of the initial site of protonation, the fragmentation reactions occurring on collisional activation are identical. By contrast, protonated heorin prepared with H⁺(H₂O)_n and H⁺(NH₃)_n as protonating agents show substantial differences. That formed by reaction of H⁺(H₂O)_n shows a much more abundant peak corresponding to loss of CH₃CO₂H. From a comparison with model compounds, and from a consideration of the three-dimensional structure of heroin, it is concluded that with H⁺(H₂O)_n as protonating agent significant protonation occurs at the acetate group attached to the alicyclic ring, leading to acetic acid loss on collisional activation, but that reaction of H⁺(NH₃)_n leads to protonation at the nitrogen function. The proton attached to nitrogen cannot interact with the acetate group and, consequently, the probability of loss of acetic acid on collislional activation is greatly reduced.     

A theoretical model investigation of the hydrogen-electrode processes of an acidic H2O2 fuel cell

Ab initio molecular-orbital (MO) self-consistent-field (SCF) computations have been carried out within the restricted Hartree-Fock (RHF) formalism on the species involved in 12 possible reaction mechanisms associated with the anodic process: H₂→2H⁺2e ^? of the hydrogen-oxygen acidic fuel cell. Such a model which represents the gas-phase reactions may be regarded as a primary standard for any future study in which the catalyst of the electrode may be included.     

Mechanism of Ethylene Migratory Insertion and Dimerization Catalyzed by δ‐Alkyl Platinum Complexes–A DFT Study

The mechanism of ethylene insertion reactions catalyzed by cationic δ‐alkyl platinum complexes has been studied at the B3LYP level of density functional theory. The initial steps of the reactions proceed via the coordination of ethylene to the reactants L₂Pt(II)R⁺, where L₂=none, (NH₃)₂, (CHNH)₂; R=H, CH₃, C₂H₅ in which ethylene coordinates strongly to the complexes PtCH⁺₃ and PtC₂H⁺₅ (coordination energies (CE) are 296.52 and 229.28 kJ/mol, respectively), while nitrogen‐containing ligands decrease the energies: Pt(NH₃)₂CH⁺₃ (CE: 180.04 kJ/mol), Pt(NH₃)₂C₂H⁺₅ (CE: 97.86 kJ/mol), Pt(CHNH)₂CH⁺₃ (CE : 176.31 kJ/mol) and Pt(CHNH)₂C₂H⁺₅ (CE: 91.00 kJ/mol). Moreover, ethylene insertion into the Pt‐alkyl bond, which is the rate‐determining step, is endothermic with barrier heights for L₂PtCH₃(C₂H₄)⁺ decreasing in the order: PtCH⁺₃ (164.18 kJ/mol)>(NH₃)₂ PtCH⁺₃ (129.95 kJ/mol)>(CHNH)₂ PtCH⁺₃ (115.27 kJ/mol), which has the same tendency for the ethyl case. The insertion product will continually undergo β‐hydride elimination, which is exothermic. On the other hand, the effects of solvent (dichloromethane, THF and benzene) are investigated with PCM method, but the inclusion of the effects in the computations only slightly affects the results. Beside that, a complete catalytic cycle for ethylene dimerization is studied in detail and the calculations agree well with known energetic and recognized tendencies.     

A theoretical study of dihydrogen bonds in small protonated rings: Aziridine and azetidine cations

B3LYP/6-311++G(d,p) calculations were used to predict some molecular properties of the C₂H₆N⁺?BeH₂, C₂H₆N⁺?MgH₂, C₃H₈N⁺?BeH₂ and C₃H₈N⁺?MgH₂ dihydrogen-bonded complexes. In these systems, it was demonstrated that the C₂H₆N⁺ and C₃H₈N⁺ protonated rings are potential candidates to bind with protonic hydrogens derived from alkaline earth metal compounds, BeH₂ and MgH₂. In terms of structural parameters and quantification of the dihydrogen bond energies, we should mention that the C₂H₆N⁺ three-membered ring provides the formation of stronger bound systems, which are 4.0 kJ mol^?1 more stables than C₃H₈N⁺ four-membered ones. As complement, the analysis of the infrared spectrum indicated that red-shifts and blue-shifts are occurring in the N–H bonds of both C₂H₆N⁺ and C₃H₈N⁺ cationic rings. However, these two vibrational shifts were also verified on BeH₂ and MgH₂, what lead us to affirm that cationic compounds derived from small nitrogen rings and earth alkaline molecules are able to form unusual dihydrogen-bonded complexes by means of distinct spectroscopic phenomena, the red-shits and blue-shifts.     

Gas-phase reactions of cationic molybdenum and tungsten monoxide with ethanol: a combined experimental/computational exercise

The ion/molecule reactions of molybdenum and tungsten monoxide cations MO⁺ (M═Mo, W) with ethanol have been studied by Fourier transform ion-cyclotron resonance mass spectrometry (FT-ICR MS) and density functional theory (DFT) calculations. As observed in the previously reported reactions of MO₂ ⁺ (M═Mo, W) towards ethanol, the dehydration of ethanol to give rise to the elimination of neutral C₂H₄ constitutes also the dominating reaction channel for the monoxides. Likewise, both systems result in a combined dehydrogenation/dehydration process, thus forming the ionic product MOC₂H₂ ⁺; moreover, the tungsten system presents two additional reaction channels: double dehydrogenation of ethanol with concomitant formation of the ionic product WO₂C₂H₂ ⁺ and the generation of C₂H₅ ⁺ which takes place by OH^? transfer from ethanol to the tungsten atom. This combined experimental/computational study of gas-phase ion molecule reactions may shed some new light on the mechanisms that occur in complex catalytic systems.