Ion-quadrupole Interaction Research Articles

Photoiodocarboxylation of Activated C═C Double Bonds with CO2 and Lithium Iodide.

The photolysis at 254 nm of lithium iodide and olefins 1 carrying an electron-withdrawing Z-substituent in CO2-saturated (1 bar) anhydrous acetonitrile at room temperature produces the atom efficient and transition metal-free photoiodocarboxylation of the C═C double bond. The reaction proceeds well for terminal olefins 1 to form the new C-I and C-C σ-bonds at the α and β-positions of the Z-substituent, respectively, and is strongly inhibited by polar protic solvents or additives. The experimental results suggest that the reaction channels through the radical anion [CO2•-] in acetonitrile, yet involves different intermediates in aqueous medium. The stabilizing ion-quadrupole and electron donor-acceptor interactions of CO2 with the iodide anion play a crucial role in the reaction course as they allow CO2 to penetrate the solvation shell of the anion in acetonitrile, but not in water. The reaction paths and the reactive intermediates involved under different conditions are discussed.

Electrostatic, sequential bond energies and structures of Li+·(N2)n complexes: computational study

The MP2 and CCSD calculations of the geometries and binding energies of the Li+·(N2)n (n = 1–4) complexes are obtained. The potential energy surface showed that these complexes exhibit one minimum state and one transition state. The mono- and di-ligated complexes exhibit linear configurations with a binding energy of 11.1 and 21.2 kcal mol−1, respectively. Trigonal planar and tetrahedral configurations are obtained for tri- and tetra-ligated complexes, respectively. The computed sequential bond dissociation energies (BDEs) of Li+·(N2)n (n = 1–4) complexes are also calculated in which the mono-ligated complex has the largest BDE value. The obtained trend is mainly dependent on the variation in the ion-quadrupole interaction of these ion complexes. These calculations predict that these complexes are of purely electrostatic nature.

Understanding Carbon Dioxide Solubility in Ionic Liquids by Exploring the Link with Liquid Clathrate Formation.

The solubilities of the quadrupolar molecules benzene and CO2 in various ionic liquids (ILs) are compared in order to determine the connection between aromatic liquid clathrate formation and CO2 dissolution in ILs. It was found that both CO2 Henry's law constants and benzene solubility are remarkably well correlated with each other and with IL molar volume, suggesting both phenomena depend more on the strength of interionic interactions between the ions of an IL rather than the identity of either ion. However, IL ion-quadrupole interactions were found to have an effect for dicyanamide ([N(CN)2 ]- ), where solubility of CO2 and benzene are affected by destabilizing and stabilizing interactions with [N(CN)2 ]- , respectively. The results suggest both solubility phenomena are related to the incorporation of the solute into an IL host network. Aromatic liquid clathrate formation thus has potential as a facile experimental probe for predicting the relative ability of ILs to physisorb CO2 .

Observation of enhanced rate coefficients in the H2++H2→H3++H reaction at low collision energies

The energy dependence of the rate coefficient of the H2++H2→H3++H reaction has been measured in the range of collision energies between kB⋅10K and kB⋅300mK. A clear deviation of the rate coefficient from the value expected on the basis of the classical Langevin-capture behavior has been observed at collision energies below kB⋅1K, which is attributed to the joint effects of the ion-quadrupole and Coriolis interactions in collisions involving ortho-H2 molecules in the j = 1 rotational level, which make up 75% of the population of the neutral H2 molecules in the experiments. The experimental results are compared to very recent predictions by Dashevskaya et al. [J. Chem. Phys. 145, 244315 (2016)], with which they are in agreement.

Quadrupole terms in the Maxwell equations: Debye-Hückel theory in quadrupolarizable solvent and self-salting-out of electrolytes.

If the molecules of a given solvent possess significant quadrupolar moment, the macroscopic Maxwell equations must involve the contribution of the density of the quadrupolar moment to the electric displacement field. This modifies the Poisson-Boltzmann equation and all consequences from it. In this work, the structure of the diffuse atmosphere around an ion dissolved in quadrupolarizable medium is analyzed by solving the quadrupolar variant of the Coulomb-Ampere's law of electrostatics. The results are compared to the classical Debye-Hückel theory. The quadrupolar version of the Debye-Hückel potential of a point charge is finite even in r = 0. The ion-quadrupole interaction yields a significant expansion of the diffuse atmosphere of the ion and, thus, it decreases the Debye-Hückel energy. In addition, since the dielectric permittivity of the electrolyte solutions depends strongly on concentration, the Born energy of the dissolved ions alters with concentration, which has a considerable contribution to the activity coefficient γ± known as the self-salting-out effect. The quadrupolarizability of the medium damps strongly the self-salting-out of the electrolyte, and thus it affects additionally γ±. Comparison with experimental data for γ± for various electrolytes allows for the estimation of the quadrupolar length of water: LQ ≈ 2 Å, in good agreement with previous assessments. The effect of quadrupolarizability is especially important in non-aqueous solutions. Data for the activity of NaBr in methanol is used to determine the quadrupolarizability of methanol with good accuracy.

Theoretical studies on hydrogen adsorption properties of lithium decorated diborene (B 2H 4Li 2) and diboryne (B 2H 2Li 2)

Using ab initio based quantum chemical calculations, we have studied the structure, stability and hydrogen adsorption properties of different boron hydrides decorated with lithium, examples of the corresponding anions being dihydrodiborate dianion, B 2H 2 2− and tetrahydrodiborate dianion, B 2H 4 2− which can be considered to be analogues and isoelectronic to acetylene (C 2H 2) and ethelene (C 2H 4) respectively. It is shown that there exists a B–B double bond in B 2H 4Li 2 and a B–B triple bond in B 2H 2Li 2. In both the complexes, the lithium sites are found to be cationic in nature and the calculated lithium ion binding energies are found to be very high. The cationic sites in these complexes are found to interact with molecular hydrogen through ion-quadrupole and ion-induced dipole interactions. In both the complexes, each lithium site is found to bind a maximum of three hydrogen molecules which corresponds to a gravimetric density of ∼23 wt% in B 2H 4Li 2 and ∼24 wt% in B 2H 2Li 2. We have also studied the hydrogen adsorption in a model one-dimensional nanowire with C 6H 4B 2Li 2 as the repeating unit and found that it can adsorb hydrogen to the extent 9.68 wt% and the adsorption energy is found to be −2.34 kcal/mol per molecular hydrogen.

Dipole Effects on Cation−π Interactions: Absolute Bond Dissociation Energies of Complexes of Alkali Metal Cations to N-methylaniline and N,N-dimethylaniline

Threshold collision-induced dissociation of M (+)( nMA) x with Xe is studied using guided ion beam mass spectrometry, where nMA = N-methylaniline and N, N-dimethylaniline and x = 1 and 2. M (+) includes the following alkali metal cations: Li (+), Na (+), K (+), Rb (+), and Cs (+). In all cases, the primary dissociation pathway corresponds to the endothermic loss of an intact nMA ligand. The primary cross section thresholds are interpreted to yield 0 and 298 K bond dissociation energies (BDEs) for ( nMA) x-1 M (+)-( nMA) after accounting for the effects of multiple ion-neutral collisions, the internal and kinetic energy distributions of the reactants, and the dissociation lifetimes. Density functional theory calculations at the B3LYP/6-31G* level of theory are used to determine the structures of these complexes, which are also used in single-point calculations at the MP2(full)/6-311+G(2d,2p) level to determine theoretical BDEs. The results of these studies are compared to previous studies of the analogous M (+)(aniline) x complexes to examine the effects of methylation of the amino group on the binding interactions. Comparisons are also made to a wide variety of cation-pi complexes previously studied to elucidate the contributions that ion-dipole, ion-induced-dipole, and ion-quadrupole interactions make to the overall binding.

Determination of the absolute values of Gibbs energy of hydration or solvation ΔG0 abs(M+ or X-)h or s of monovalent (alkali metal and halide) ions and other thermodynamic parameters in aqueous and non-aqueous solvents using a single standard state and analysis of ΔG0 abs(M+ or X-)h or s values based on cluster-ion solvation method

or X - ) h or s and other thermodynamic parameters in aqueous and non-aqueous solvents (methanol, ethanol, n-propanol, isopropanol, n-butanol, ethylene glycol, propylene carbonate (PC), N-methyl formamide (NMF), acetone, tetrahydrofuran (THF), 1,4-dioxan, acetonitrile) were determined directly using modified Born equation and a single standard state [i.e. AG° and ΔH 0 (but not ΔS 0 ) of H 2 gas and other elements to be zero in their elementary standard states at 1 atm. pressure (1 bar) and 298 K]. The ΔH 0 abs (M + or X - ) h or s and ΔG 0 (M + or X - ) h or s values are calculated considering ion-dipole, ion-quadrupole interactions and without considering the interaction terms. Very few data are available in non-aqueous solvents for comparison. Most of the single ion values (particularly for the anions) suffer from limitations associated with the erroneous principle of division of solvation energies ΔG 0 h or s (MX) or ΔΗ 0 h or s (MX) of electrolytes into single ion values. ΔG 0 (M + or X - ) h values determined using cluster-ion solvation data have also been presented. The values have been claimed to be most accurate in recent years. However, the method involves a number of assumptions of doubtful validity and the values cannot be regarded to be equivalent to ΔG 0 (Μ + or X - ) h or determined by other workers using different methods. Coupling the values of ΔG 0 (M + or X - ) h or s and ΔH 0 (M + or X - ) h or s with ΔG 0 (M + or X - ) g and ΔH 0 (M + or X - ) g values in the gaseous state, ΔG 0 (M + or X - ) Water or org. solvent' ΔH 0 (Μ + or X - ) water or org. solvent and ΔS 0 (M + or X - ) water or org. solvent [values in water and in organic solvents] are determined.

Dynamical Constraints and Adiabatic Invariants in Chemical Reactions

For long-range electrostatic potentials and, more generally, when the topography of the potential energy surface is locally simple, the reaction path coordinate is adiabatically separable from the perpendicular degrees of freedom. For the ion-permanent dipole and ion-quadrupole interactions, the Poisson bracket of the adiabatic invariant decreases with the interfragment distance more rapidly than the electrostatic potential. The smaller the translational momentum, the moment of inertia of the neutral fragment, and the dipole or quadrupole moments are, the more reliable the adiabatic approximation is, as expected from the usual argumentation. Closed-form expressions for an effective one-dimensional potential in an adiabatic Hamiltonian are given. Connection with a model where the decoupling is exact is obtained in the limit of an infinitely heavy dipole. The dynamics is also constrained by adiabatic invariance for a harmonic valley about a curved reaction path, as shown by the reaction path Hamiltonian method. The maximum entropy method reveals that, as a result of the invariance properties of the entropy, constraints whose validity has been demonstrated locally only subsist in all parts of phase space. However, their form varies continuously, and they are not necessarily expressed in simple terms as they are in the asymptotic region. Therefore, although the influence of adiabatic invariance has been demonstrated at asymptotically large values of the reaction coordinate only, it persists in more interesting ranges.

CO 2 adsorption in Y and X zeolites modified by alkali metal cation exchange

Ion exchange was performed on NaY and NaX zeolites with alkali metal cations Li +, K +, Rb +, and Cs + and studied by adsorption of CO 2. This is the first study to examine adsorption equilibrium isotherms and capacities of CO 2 on the alkali metal series for both Y and X zeolites under mild conditions. CO 2 capacity increased as Cs < Rb ≈ K < Li ≈ Na for Y zeolites. For X zeolites, the capacity for CO 2 increased in the order Cs < Rb < K < Na < Li (the order of decreasing ionic radii). For both zeolites the larger cation forms (Cs, Rb, K) exhibited strongly nonlinear concave downward isotherms, which is indicative of strong interactions between CO 2 and the zeolite. This is consistent with an increased basicity of the framework compared to the smaller cation forms, given that CO 2 is a weakly acidic gas. This is also reflected by the Henry’s law slopes obtained from the Toth isotherm equation. Our measurements show that, in general, CO 2 capacities are greatest for the Li forms, in which the ion–quadrupole interaction is dominant. Adsorption equilibrium measurements of CO 2 on each ion-exchanged material reveal behaviors and trends based on cation size and acid–base surface properties that can have an important impact on tuning adsorptive properties of zeolites by ion exchange.

Threshold photoelectron photoion coincidence spectroscopy and selected ion flow tube cation-molecule reaction studies of cyclic-C4F8

Using tunable vacuum-UV radiation from a synchrotron, the threshold photoelectron and threshold photoelectron photoion coincidence (TPEPICO) spectra of cyclic-C4F8 in the range 11-25 eV have been recorded. The parent ion is observed very weakly at threshold, 11.60 eV, and is most likely to have cyclic geometry. Ion yield curves and branching ratios have been determined for five fragments. Above threshold, the first ion observed is C3F5+, at slightly higher energy C2F4+, then successively CF+, CF2+ and CF3+ are formed. The dominant ions are C3F5+ and C2F4+, with the data suggesting the presence of a barrier in the exit channel to production of C3F5+ whilst no barrier to production of C2F4+. In complementary experiments, the product branching ratios and rate coefficients have been measured in a selected ion flow tube (SIFT) at 298 K for the bimolecular reactions of cyclic-C4F8 with a large number of atomic and small molecular cations. Below the energy where charge transfer becomes energetically allowed, only one of the ions, CF2+, reacts. Above this energy, all but one of the remaining ions react. Experimental rate coefficients are consistently greater than the collisional values calculated from modified average dipole orientation theory. The inclusion of an additional ion-quadrupole interaction has allowed better agreement to be achieved. With the exception of N+, a comparison of the fragment ion branching ratios from the TPEPICO and SIFT data suggest that long-range charge transfer is the dominate mechanism for reactions of ions with recombination energy between 12.9 and 15.8 eV. For all other ions, either short-range charge transfer or a chemical reaction, involving cleavage and making of new bond(s), is the dominant mechanism.

Isomeric states of polar molecules on ionic surfaces: electrostatic model and FTIR studies

Interaction of diatomic (polar) molecules with the surface of ionic solids is analysed by means of an electrostatic model which takes into account ion–dipole and ion–quadrupole interactions. This model was found to be capable of predicting the geometry of the adsorption complex, formation of isomeric states and relevant features of characteristic vibrational spectra. The theoretical model is demonstrated by considering the case of CO adsorbed on cation-exchanged zeolites for which a wealth of experimental data is available from both, vibrational spectroscopy and adsorption calorimetry. However, extension to other systems should be fairly straightforward.

Quantum scattering and adiabatic channel treatment of the low-energy and low-temperature capture of a rotating quadrupolar molecule by an ion.

The capture rate coefficients of homonuclear diatomic molecules (H(2) and N(2)) in the rotational state j=1 interacting with ions (Ar+ and He+) are calculated for low collision energies assuming a long-range anisotropic ion-induced dipole and ion-quadrupole interaction. A comparison of accurate quantum rates with quantum and state-specific classical adiabatic channel approximations shows that the former becomes inappropriate in the case when the cross section is dominated by few partial contributions, while the latter performs better. This unexpected result is related to the fact that the classical adiabatic channel approximation artificially simulates the quantum effects of tunneling and overbarrier reflection as well as the Coriolis coupling and it suppresses too high values of the centrifugal barriers predicted by a quantum adiabatic channel approach. For H2(j=1)+Ar+ and N(2)(j=1)+He+ capture, the rate constants at T-->0 K are about 3 and 6 times higher than the corresponding values for H2(j=0)+Ar+ and N(2)(j=0)+He+ capture.

Unusual Thresholds and Isotope Effects in Al+ + H2/D2/HD Reactions

Ab initio quantum chemistry is used to generate a three-dimensional reactive potential-energy surface for the collision of 1S Al+ ions with ∑g H2 molecules. This surface, in a tessellated and locally interpolated form, is used to generate forces for classical trajectory simulations of the 3.98 eV endothermic Al+ + H2 f AlH+ + H reactions with initial conditions appropriate to a thermal H2 sample and an Al+ beam of specified center of mass collision kinetic energies in the 3-20 eV range. Our findings indicate that the reaction occurs not on (or near) the collinear path, which has no barrier above the reaction endothermicity, but via a near-C2V insertive path which spontaneously breaks C2V symmetry via second-order Jahn-Teller distortion to permit flux to evolve to AlH+ + H products. The strong propensity to “avoid” the collinear path and to follow a higherenergy route is caused, at long range, by the ion-quadrupole interaction between Al+ and H2 and, at shorter range, by favorable overlap between the H2 σu and Al+ 3p obitals. Examination of a large number of trajectories shows clearly that reactive collisions (1) lose much of their initial kinetic energy to the repulsive ionmolecule interfragment potential as the closed-shell Al+ and H2 approach, (2) transfer significant energy to the H-H stretching coordinate, thus weakening the H-H bond, (3) convert initial H2 rotational motion as well as Al+ to H2 collisional angular momentum into rotational angular momentum of the HAlH+ complex, “locking” the H2 moiety into the insertive near-C2V geometry about which twisting motion occurs, and (4) allow the Al+ ion to form a new bond with whichever H atom is nearest it when the system crosses into regions of the energy surface where the H-Al-H asymmetric stretch mode becomes second-order JahnTeller unstable, thus allowing fragmentation into AlH+ + H. These findings, combined with considerations of kinematic factors that distinguish among H2, D2, and HD, allow us to explain certain unusual threshold and isotope effects seen in the experimental reaction cross-section data on these reactions.

Measured and calculated mobilities of cluster ions drifting in helium and in nitrogen

New experimental results are presented for the mobilities of (1) the H 3O +(H 2O) 3 cluster ion drifting in He (the reduced zero-field mobility K 0 (0) is 11.5 ± 0.4 cm 2 V −1 s −1, (2) NO +(CH 3COCH 3) n cluster ions drifting in He ( K 0 (0) = 7.5 ± 0.4 cm 2 V −1 s −1 for n = 2, K 0 (0) = 7.3 ± 0.5 cm 2 V −1 s −1 for n = 3), and (3) the NO +(CH 3CN) 2 cluster ion drifting in N 2 ( K 0 (0) = 1.70 ± 0.06 cm 3 V −1 s −1). These results together with other recently reported cluster ion mobilities in He are quantitatively explained using the hard-sphere collision model by von Helden et al. ( J. Phys. Chem. 97 (1993) 8182–8192). The role of ion-induced dipole interactions is investigated and shown to be minor for the mobilities of all but the smallest ions in He. The existing data on cluster-ion mobilities in N 2, including the result here, are systematized. As a result of the stronger polarizability of N 2, the hard-sphere collision model does not agree with the data, and a better explanation is obtained using a simple model that includes ion-induced dipole interactions. The size of the cluster has only a minor effect on the mobility in N 2. The remaining discrepancies between the measured and calculated results are attributed to ion-quadrupole or dipole induced-dipole interactions.

Ion broadening of dense-plasma spectral lines including field-dependent atomic physics and the ion quadrupole interaction.

We examine the theoretical line spectra from hydrogenlike argon in the electron-number-density range of ${10}^{24--}$${10}^{25}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$ and at a temperature corresponding to kT=800 eV. At these high densities it is important to address the relevance of higher-order plasma-ion microfield effects on the spectral line shape. We begin by calculating spectral line shapes using electric-field-dependent matrix elements that are constructed from wave functions which are solutions of Schr\"odinger's equation for hydrogenic ions in a uniform field. This provides a suitable basis for including microfield spatial nonuniformities by considering the quadrupole term in the radiator-perturbing ion interaction. Field gradients are calculated in an approximation that takes ion-ion correlations into account. We examine the consequences of these effects as well as of mixing between the adjacent Stark manifold on the Lyman-\ensuremath{\alpha} and Lyman-\ensuremath{\beta} lines of hydrogenlike argon.

Complex formation in X + + H 2 collisions. Statistical estimation of ion-quadrupole capture rate constants

The capture cross section and rate constant of ion-molecule collisions have been studied in the case when the molecule is diatomic and has a vanishing dipole moment but a nonvanishing quadrupole moment obtained from quantum chemistry as a function of bond length. In addition the ion-induced dipole interaction is accounted for. Calculations have been carried out at three levels of theory: variational transition state theory, effective potential theory and adiabatic capture theory. In the latter the channels are defined by the vib-rot states of the diatomic. Application has been made to Ar + or N + + H 2 collisions. The results show that in this case the ion-induced dipole interaction is far more significant than the ion-quadrupole interaction. The roles of vibrational-rotational coupling and orbital angular momentum are considered by comparison of weak ( L orb conserving) and strong coupling theories. The range of validity of the perturbation treatment of the coupling is analyzed. Special attention is directed to the magnitude of the quantum effects introduced through the channel eigenvalues of the adiabatic capture theories.

A three-dimensional potential energy surface for the reaction N+(3P)+H2(1 Σ+g) ⇔ NH+ (X 2Π)+H(2S)

Extensive ab initio calculations have been performed on the reaction N+3(P)+H21(Σ+g)⇔NH+ (X 2Π)+H(2S), using complete-active-space self-consistent-field and multireference contracted configuration interaction methods. The 752 calculated energy points belonging to the 1 3A″ surface were fitted to an analytical potential energy surface, with an average least-squares deviation of only 0.026 eV (2.5 kJ/mol). A key to this accurate fit of the surface, which does include minima as deep as 6 eV, is the use of R−n polynomials in the asymptotic region, and Rn polynomials in the deep minima regions. The calculated reaction endothermicity is 0.03 eV, after correcting for the differences in zero point vibrational energies. This is in agreement with the essentially thermoneutral reaction enthalpy, obtained in recent experiments. An important feature of the potential energy surface is the anisotropy in the reactant channel, arising from the ion–quadrupole interaction.

A low energy quasiclassical trajectory study of N++H2. Potential energy surface effects

A low energy quasiclassical trajectory study has been performed on three potential energy surfaces, obtained by modifying the recent ground state ab initio potential energy hypersurface by Wilhelmsson et al. for the N+(3P)+H2(1Σ+g)→NH+ (2Π)+H(2S) reaction. The importance of explicit consideration of the asymptotic ion–induced dipole and ion–quadrupole interactions in the entrance channel is demonstrated. Reaction cross sections as a function of collision energy (approximately in the range 0.06–0.4 eV in c.m.) are presented.

Trajectory calculations of ion–molecule momentum transfer rate constants

A classical trajectory method is used to calculate thermal energy momentum transfer rate constants for ions in polar and nonpolar gases. The calculations include the consideration of noncapture scattering. For ions in nonpolar gases, the anisotropy of the polarizability and the ion–quadrupole interaction are also included in the calculations. The results show that the noncapture scattering plays an important role in momentum transfer for ions in both polar and nonpolar neutral gases. For ions in anisotropic nonpolar gases, both the anisotropy of the polarizability and the ion–quadrupole potential are important contributors to the momentum transfer rate constants. The theoretical rate constants are in good agreement with a large collection of experimental results. The theoretical results for polar gases are parametrized to an analytical expression which serves as a useful tool for estimating thermal energy ion–polar molecule momentum transfer rate constants. The present theoretical model is more realistic and provides a more accurate estimation of ion–molecule momentum transfer rate constants than previous theoretical treatments.