Dipole-induced Dipole Interactions Research Articles

Fragmentation dynamics of argon clusters (Arn, n=2 to 11) following electron-impact ionization: Modeling and comparison with experiment

The fragmentation dynamics of argon clusters ionized by electron impact is investigated for initial cluster sizes up to n = 11 atoms. The dynamics of the argon atoms is modeled using a mixed quantum-classical method in which the nuclei are treated classically and the transitions between electronic states quantum mechanically. The potential-energy surfaces are derived from a diatomics-in-molecules model with the addition of the induced dipole-induced dipole and spin-orbit interactions. The results show extensive and fast fragmentation. The dimer is the most abundant ionic fragment, with a proportion increasing from 66% for n = 2 to a maximum of 95% for n = 6 and then decreasing down to 67% for n = 11. The next abundant fragment is the monomer for n < 7 and the trimer otherwise. The parent ion dissociation lifetimes are all in the range of 1 ps. Long-lived trajectories appear for initial cluster sizes of seven and higher, and favor the formation of the larger fragments (trimers and tetramers). Our results show quantitative agreement with available experimental results concerning the extensive character of the fragmentation: Ar+ and Ar2(+) are the only ionic fragments for sizes up to five atoms; their overall proportion is in quantitative agreement for all the studied sizes; Ar2(+) is the main fragment for all sizes; stable Ar3(+) fragments only appear for n > or = 5, and their proportion increases smoothly with cluster size from there. However, the individual ionic monomer and dimer fragment proportions differ. The experimental ones exhibit oscillations with initial cluster size, with a slight tendency to decrease on average for the monomer. In contrast our results show a monotonic, systematic evolution, similar to what was found in our earlier studies on neon and krypton clusters. Several hypotheses are discussed in order to find the origin of this discrepancy. Finally, the metastable II(1/2)u and II(1/2)g states of Ar2(+) are found to decay with a lifetime of 3.5 and 0.1 ps, respectively, due to spin-orbit coupling. The difference with the commonly accepted microsecond range value for rare-gas dimer ions could originate from the role of autoionizing states in the formation of the parent ions.

Modelization of the fragmentation dynamics of krypton clusters (Krn,n=2–11) following electron impact ionization

We present the first prediction for the fragmentation dynamics following electron impact ionization of neutral krypton clusters from 2 to 11 atoms. Fragment proportions and parent ion lifetimes are deduced from a molecular dynamics with quantum transitions study in which the nuclei are treated classically and the transitions between electronic states quantum mechanically. The potential-energy surfaces are derived from a diatomics-in-molecules model to which induced dipole-induced dipole and spin-orbit interactions are added. The results show surprisingly fast and extensive fragmentation for clusters of such a heavy atom, although not as extensive as in the case of neon clusters studied previously [D. Bonhommeau et al., J. Chem. Phys. 123, 54316 (2005)]. The parent ion lifetimes range from 2.8 to 0.7 ps, and the most abundant fragment is Kr(2) (+) for all studied sizes, followed by Kr(+) for sizes smaller than 7 atoms and by Kr(3) (+) for larger sizes. Trimer and larger fragments are found to originate from the lower electronic states of parent ions. The comparison with preliminary results from experiments on size-selected neutral clusters conducted by Steinbach et al. (private communication) reveal a good agreement on the extensive character of the fragmentation. It is checked that the additional internal energy brought by the helium scattering technique used for size selection does not affect the fragment proportions. In addition, the existence of long-lived trajectories is revealed, and they are found to be more and more important for larger cluster sizes and to favor the stabilization of larger fragments. The implications of this work for microsecond-scale dynamics of ionized rare-gas clusters are discussed. In particular, given the extent of fragmentation of the parent clusters and the fast kinetics of the whole process, the small cluster ions that exhibit a monomer loss in the microsecond time window must originate from much larger neutral precursors. The decay rate of the II(12)(u) state of the ionic dimer Kr(2) (+) by spin-orbit coupling is found to be of the order of 3 ps, in contrast to the expected tens of microseconds, but only reasonably faster than the corresponding state of HeNe(+). Finally, the spin-orbit interaction strongly affects both the Kr(+)Kr(2) (+) ratio and some of the characteristic times of the dynamics, especially for smaller sizes, but not the overall dependence of the fragment proportions as a function of cluster size.

Fragmentation dynamics of ionized neon clusters (Nen,n=3–14) embedded in helium nanodroplets

We report a theoretical study of the nonadiabatic fragmentation dynamics of ionized neon clusters embedded in helium nanodroplets for cluster sizes up to n=14 atoms. The dynamics of the neon atoms is modeled using the molecular dynamics with quantum transitions method of Tully [J. Chem. Phys. 93, 1061 (1990)] with the nuclei treated classically and transitions between electronic states quantum mechanically. The potential-energy surfaces are derived from a diatomics-in-molecules model to which induced dipole-induced dipole interactions are added. The effect of the spin-orbit interaction is also discussed. The helium environment is modeled by a friction force acting on charged atoms whose speed exceeds the critical Landau velocity. The dependence of the fragment size distribution on the friction strength and on the initial nanodroplet size is investigated. By comparing with the available experimental data obtained for Ne3+ and Ne4+, a reasonable value for the friction coefficient, the only parameter of the model, is deduced. This value is then used to predict the effect of the helium environment on the dissociation dynamics of larger neon clusters, n=5-14. The results show stabilization of larger fragments than in the gas phase, but fragmentation is not completely caged. In addition, two types of dynamics are characterized for Ne4+: fast and explosive, therefore leaving no time for friction to cool down the process when dynamics starts on one of the highest electronic states, and slower, therefore leading to some stabilization by helium when it starts on one of the lowest electronic states.

Analysis of binary adsorption of polar and nonpolar molecules in narrow slit-pores by mean-field perturbation theory

In the present research study, we present the development of a model for predicting the adsorption of binary mixtures of nonpolar molecules, as well as polar molecules, based on density functional theory with mean-field approximation in narrow slit-pores. The first system under consideration is comprised of a binary mixture of nonpolar molecules, modeled by considering intermolecular dispersion forces, whereas the second system comprised of a binary mixture of polar molecules is modeled by considering orientation averaged electrostatic interactions, namely dipole-dipole and dipole-induced dipole interactions as well as dispersion interactions. An explicit equation for the Helmholtz free energy of the pore phase binary fluid mixture is derived. The proposed model is used to simulate the selective sorption of ethane from an ethane-methane mixture and water from a methanol-water mixture in the slit-pore. The simulated results are interpreted by studying the relative contributions of fluid-wall and fluid-fluid interactions. Finally, simulation results obtained are compared with the results of existing models and molecular simulations in the literature.

Multidimensional infrared spectroscopy for molecular vibrational modes with dipolar interactions, anharmonicity, and nonlinearity of dipole moments and polarizability

We present an analytical expression for the linear and nonlinear infrared spectra of interacting molecular vibrational motions. Each of the molecular modes is explicitly represented by a classical damped oscillator on an anharmonic multidimensional potential-energy surface. The two essential interactions, the dipole-dipole (DD) and the dipole-induced-dipole (DID) interactions, are taken into account, and each dipole moment and polarizability are expanded to nonlinear order with respect to the nuclear vibrational coordinate. Our analytical treatment leads to expressions for the contributions of anharmonicity, DD and DID interactions, and the nonlinearity of dipole moments and polarizability elements to the one-, two-, and three-dimensional spectra as separated terms, which allows us to discuss the relative importance of these respective contributions. We can calculate multidimensional signals for various configurations of molecules interacting through DD and DID interactions for different material parameters over the whole range of frequencies. We demonstrate that contributions from the DD and DID interactions and anharmonicity are separately detectable through the third-order three-dimensional IR spectroscopy, whereas they cannot be distinguished from each other in either the linear or the second-order IR spectroscopies. The possibility of obtaining the intra- or intermolecular structural information from multidimensional spectra is also discussed.

Ultrasonic study on binary liquid mixtures between some bromoalkanes and hydrocarbons

Densities and ultrasound velocities for the binary mixtures of 1-bromobutane + benzene and 1,4-dimethylbenzene and of 1-bromopentane + cyclohexane and benzene have been measured at 308.15 K. Adiabatic compressibilities ( β ad), and Wada’s constants ( W) have also been evaluated as a function of composition. The ultrasound velocities decrease, attains a minimum and then increase with increase in mole fractions of hydrocarbons in the binary mixtures except in the case of 1-bromopentane + benzene binary mixtures where the variation is just the reverse. Dependence of adiabatic compressibilities with mole fractions of hydrocarbons is sigmoid. The non-ideal behaviour of the systems studied is explained on the basis of dipole-induced dipole interactions.

The stabilizing contribution of thymine in duplexes of (dA)24 with (dU)24, (dT)24, (dU12–dT12), (dU–dT)12, (dU2–dT2)6, or (dU3–dT3)4: Nearest neighbor and next‐nearest neighbor effects

Ultraviolet melting curves are used to determine the effect of the pyrimidine 5-methyl group on the stability of duplexes of (dA)(24) with (dU)(24), (dT)(24), (dU(12)-dT(12)), (dU-dT)(12), (dU(2)-dT(2))(6), and (dU(3)-dT(3))(4). Substitution of a T for a U results in an increase in stability, which is attributed to an increase in strength of dipole-induced dipole and dispersion (van der Waals) interactions. Significant additional enhancement occurs when two T residues are adjacent. A further increase in the number of adjacent T's has a relatively slight effect on T(m). The sequence effect appears to be largely attributable to an increment in dispersion forces. The CD spectra of the duplexes are all closely similar except in the region between 260 and 290 nm. A band near 272 nm associated with the presence of U in the spectrum of (dA)(24).(dU)(24) decreases in intensity when T's are incorporated in the pyrimidine strand. The band is completely replaced in the spectrum of (dA)(24).(dT)(24) with a new maximum at 282 nm and a minimum at 268 nm, both of lower magnitude. The emergence of the two new bands is correlated with the presence of adjacent T's once more, and only two adjacent T's appear necessary for a major part of the change to occur. The degree of cation release on thermal dissociation of the oligomer dimers ranges from Deltai = 0.14 to 0.16, about the same or slightly less than values reported for polynucleotide duplexes and less than predicted from theoretical calculations.

Raman spectra and structure of molten fluorides: The binary mixtures MF 2–AF (M = Zn, Pb; A = K, Cs) and the compounds K 2ZnF 4 and K 4PbF 6

Raman spectra of molten binary mixtures of ZnF 2–AF (A = K, Cs) and of PbF 2–KF have been measured at temperatures up to 1000 °C. Composition and temperature dependent measurements are related to the structure of these melts. The changes of vibrational modes upon melting the polycrystalline compound K 2ZnF 4 and K 4PbF 6 have been also measured. For the ZnF 2–AF melt mixtures rich in AF a strong polarized band at ∼471 cm −1 is assigned to the ZnF 4 2 - ‘tetrahedral’ species. With increasing ZnF 2 mole fraction the polarized band shifts to high frequencies by ∼10 cm −1 indicating the formation of either a trigonal ( ZnF 3 - ) and/or bridged ‘tetrahedral’ ( Zn 2 F 6 2 - ) species. These species are also present in ZnF 2-rich melt mixtures in equilibrium with a variety of distorted ‘octahedral’ ( ZnF 6 4 - ) species with a characteristic polarized band at ∼364 cm −1. Most probably the structure of very rich in ZnF 2 melts and of pure molten ZnF 2 is predominated by bridged ‘octahedra’ forming a loose network. The spectra of PbF 2–KF melt mixtures show mainly one polarized band at ∼400 cm −1 whose position is practically independent of composition. It appears that in KF-rich melt mixtures the structure is predominated by independent anionic species Pb m F 2 m + n n - of unknown stoichiometry and symmetry. With increasing PbF 2 mole fraction the anionic species interact with each other by sharing fluorides and forming larger structures with short lifetimes. The relative intensities of the isotropic and anisotropic spectra of both sets of the ZnF 2–KF and PbF 2–KF binaries have been calculated and are correlated to cation shielding effects and to dipole-induced dipole interactions in these melts.

Raman spectra and structure of PbCl 2–ACl (A = K, Cs) melts

Quantitative Raman spectra of molten PbCl 2–ACl (A = K, Cs) mixtures have been measured at different compositions and at temperatures up to 680 °C. Spectral changes upon melting the Cs 4PbCl 6, CsPbCl 3, KPb 2Cl 5 and PbCl 2 solids have been also measured. All spectra of melts are mainly characterized by an isotropic (polarized) ν P and an anisotropic (depolarized) ν D band. The intensity and position of the ν P (∼237 ± 2 cm −1) and ν D (∼113 ± 3 cm −1) bands remain practically constant at X PbCl 2 ⩽ 0.5 indicating that the structure is predominated by coordination polyhedra of the type Pb n Cl 3 n n - ( n ⩽ 4). With increasing PbCl 2 mole fraction the ν P and ν D bands shift to the “red” and the “blue”, respectively, reaching the corresponding values of 215 and 132 cm −1 in pure molten PbCl 2. Furthermore, the intensity ratio of the anisotropic to isotropic spectra increases indicating contributions to the scattering intensity arising from dipole–induced-dipole interactions in these melts.

I*(2P1/2) and Cl*(2P1/2) Production from Chloroiodobenzenes in the Ultraviolet

The relative quantum yields of $I*(^2P_{1/2})$ and $Cl*(^2P_{1/2})$ production, $\phi*(I)$ and $\phi*(Cl)$, respectively, have been measured at four different ultraviolet excitation wavelengths, e.g., 222, 236, 266, and 280 nm in the photodissociation of o-, m-, and p-chloroiodobenzenes. The measured I* and Cl* quantum yields are, with some exceptions, higher than those obtained, respectively, from iodobenzene and chlorobenzene, at the same wavelengths. While at most wavelengths the major fraction of the iodine atoms is produced in the excited state, the opposite is true for the chlorine atoms. Both direct and indirect dissociation pathways are involved in the production of I* atoms whereas Cl* is produced only by indirect pathways since direct excitation of the $\sigma$*$(C-Cl) \leftarrow n(Cl)$ transition is not possible at these wavelengths. The halogen atom in the ortho position is found to be most effective in enhancing the yield of the other spin-orbit excited halogen atom in the photolysis. While the nature of the initial transition, the extent of intersystem crossing in the excited states and the exit channel effects need to be considered in interpreting the quantum yield results, some factors seem to be more effective in influencing the final outcome. Induced dipole-induced dipole and quadrupolequadrupole interactions between the two halogen atoms (I and Cl in this case) seem to play an important role in the exit channel dynamics. These electrostatic interactions facilitate the intersystem transfer in the excited state and subsequent production of the spin-orbit excited halogen atoms.

Close collisions in the two-dimensional Raman response of liquid carbon disulfide

The fifth-order 2D Raman response of a liquid is calculated taking all possible interaction induced effects into account. Next to dipole-induced dipole interactions, close collision effects due to induced multipoles and electron overlap are found to give a significant contribution to the response of liquid carbon disulfide. A correct prediction of the spectrum is impossible, when these effects are not properly taken into account. The calculated response is found to be in good agreement with some of the most recent experiments.

Quantitative structure-property relationships for vapor pressures of polybrominated diphenyl ethers

Based on quantum chemical descriptors, by the use of partial least squares regression, quantitative structure-property relationship models for subcooled liquid vapor pressures ( P L ) of polybrominated diphenyl ether (PBDE) congeners were developed. The Q cum 2 value of the optimal model obtained is as high as 0.993, indicating a good predictive ability and robustness of the model. Although disagreements were observed between the predicted log P L values and log P L values of validation set, the model obtained can still be used for estimating P L of other PBDE congeners, considering the fact that accurate P L values for compounds with low volatility are extremely difficult to determine experimentally. Intermolecular dispersive interactions play a leading role in governing the values of P L , followed by electrostatic, dipole-dipole and dipole-induced dipole interactions. Intermolecular dispersive interactions also govern the values of enthalpies of vaporization.

SF 6 and its clusters in solid parahydrogen studied by infrared spectroscopy

The triply degenerate stretching vibration of sulfur hexafluoride and its clusters in solid parahydrogen at cryogenic temperatures is studied using Fourier transform infrared spectroscopy. The observed spectra are compared with theoretical spectra constructed on the basis of the intermolecular resonant dipole–dipole and the dipole–induced-dipole interactions. The absorptions due to monomer, dimer, trimer, and tetramer are discussed individually.

Infrared matrix isolation spectra of SF 6 dimers

The infrared spectra of 32 SF 6, 33 SF 6 and 34 SF 6 dimers were studied in argon and nitrogen matrices. The spectra of SF 6 dimers of like and unlike isotopomers were also calculated taking into account the resonance dipole–dipole and dipole-induced dipole interactions between two triply degenerate oscillators. Two absorption bands with site structure are observed for ( 32 SF 6) 2, ( 33 SF 6) 2 and ( 34 SF 6) 2 in argon; the ν X, Y band is blue shifted and the ν Z band is red shifted from the ν 3 SF 6 band in accordance with calculated spectra. Three and two components of the predicted quadruplets are identified for 32 SF 6– 34 SF 6, 32 SF 6– 33 SF 6 , respectively. In the spectra of (SF 6) 2 in nitrogen matrices the splitting of ν X, Y component of the resonance doublet was observed.

Optimization of Xe adsorption kinetics in single walled carbon nanotubes

Closed end (10, 10) single walled carbon nanotubes (SWNTs) have been opened by oxidation at their ends and at wall defect sites, using ozone. Oxidation with ozone, followed by heating to 973 K to liberate CO and CO2, causes etching of the nanotube surface at carbon atom vacancy defect sites. The rate of adsorption of Xe has been carefully measured as a function of the degree of nanotube etching by ozone. It is found that a level of etching corresponding to wall openings of about 5–7 Å radius is optimal for maximizing the rate of Xe adsorption. Beyond this level of etching, the rate of Xe adsorption decreases as the surface area of the SWNTs decreases due to further carbon atom removal. Both experiment and modeling show that the presence of polar oxidized groups, such as –COOH or –COR groups, with dipole moments in the range 1.5–3.0 D at the perimeter of the defect sites, causes a retardation of the rate of Xe adsorption due to dipole-induced dipole interactions. This effect is larger for smaller radius defect sites and decreases as the defect sites increase in size beyond about 7 Å radius. At large defect radii, the energetic profile of the adsorption pathway controls the physisorption rate. Modeling shows that after Xe adsorption has been completed inside the nanotubes, then Xe clusters begin to form on the outer surface of the nanotubes at the defect sites where polar groups are present. The Xe clustering effect also occurs to a smaller degree when the defect sites are not decorated by polar groups. The experiments and modeling demonstrate how one may optimize the rate of adsorption of a gas into nanotubes by the adjustment of the size and polar character of the vacancy-site entry ports in the walls of the nanotubes.

Application of linear solvation energy relationships to polymeric pseudostationary phases in micellar electrokinetic chromatography.

Polymerized sodium 11-acrylamidoundecanoate (poly(Na 11-AAU)) was used as a pseudostationary phase (PSP) for micellar electrokinetic chromatography to separate uncharged compounds. The polymer PSP showed signifcantly different solute migration behaviors from conventional micelles including sodium dodecyl sulfate and poly (sodium 10-undecylenate), giving high separation efficiencies (>200000 theoretical plates/m). Linear solvation energy relationships were used to evaluate and characterize the chemical interactions that influence the retention behavior in the poly (Na 11-AAU) micellar system. It was found that the solute volume and solute hydrogen bond basicity mainly influenced the retention. The characteristic feature of the poly (Na 11-AAU) micellar system is that the micelle has a significantly higher capacity for dipole-dipole and dipole-induced dipole interactions as well as a slightly higher capacity for electron pair interactions than the aqueous phase. Due to its unique selectivity, the poly(Na 11-AAU) micellar system would become an attractive new option for selectivity optimization on methods development.

A Molecular Dynamics Simulation Study of Dipole Correlation in the Isotropic Phase of the Mesogens me5NF and GGP5Cl

Molecular dynamics simulations of the molecules me5NF and GGP5Cl have been undertaken to study dipole correlation in the isotropic phase. The simulations use an all-atom force field developed specifically for these molecules, together with a full treatment of the long range electrostatic interactions via an Ewald sum. me5NF exhibits a preference for anti-parallel dipole association as seen through the distance dependent correlation function g1(r). However, GGP5Cl shows no marked preference for parallel or anti-parallel dipole association. Both molecules show the presence of distinct parallel and anti-parallel dipole dimers in the liquid phase. For me5NF the dominant molecular pair configurations arise from favourable quadrupolar interactions between an unsubstituted phenyl ring and a second phenyl ring with fluorine and cyano substituents. In GGP5Cl, which has two fluorinated phenyl rings, molecules in the liquid phase show an intramolecular preference for an anti-parallel arrangement of C-F bond dipoles, which is absent in the gas phase. Kirkwood correlation factors, g1, have been calculated from the simulations data. For me5NF, the g1 result is in excellent agreement with existing experimental data. However, the g1 result for GGP5Cl is in error. It is suggested that this discrepancy arises due to a failure to model correctly the dipole-induced dipole interactions that arise in this molecule.

Speed of Sound and Isentropic Compressibilities of N-Methylcyclohexylamine with Benzene and Substituted Benzenes at 303.15 K

New experimental sound velocity and density data for binary mixtures of N-methyl-cyclohexylamine with benzene, toluene, o-xylene, m-xylene, p-xylene, chlorobenzene, bromobenzene and nitrobenzene at 303.15K have been reported. The sound velocity data were also used to compute the isentropic compressibilities (Ks ). The deviation in isentropic compressibilities (ΔKs ) from ideal behaviour suggests that the existence of weak dipole-induced dipole and dipole-dipole interactions between unlike molecules.

Theoretical description of the nonlinear response functions associated with eight distinctive three-dimensional vibrational spectroscopies

The three-dimensional (3D) vibrational spectroscopies are theoretically considered in terms of the associated nonlinear response functions. Since the 3D vibrational spectroscopy involves three vibrational coherence evolutions in the ground electronic state, it is found that there are eight distinctive possibilities when a vibrational coherence state can be created via an infrared field–matter interaction or two off-resonant optical field–matter interactions via Raman. The nonlinear response functions associated with eight distinctive 3D vibrational spectroscopies, where seven of them are novel methods, are presented and expressed in terms of the linear response functions by taking the lowest-order contributions. The analytic expressions of the 3D Fourier spectra are obtained. By using the results, how to utilize the 3D vibrational spectroscopic methods to measure the higher-order vibrational mode coupling arising from the anharmonicity of the multidimensional potential energy surface as well as from the nonlinearity of the dipole moment or polarizability with respect to the vibrational degrees of freedom is discussed. Numerical calculations of the results for a three-oscillator model system are presented, and a few characteristic peaks uniquely appearing in the 3D vibrational spectra are discussed in detail. Finally, the third-order nonlinear terms of dipole moment and polarizability are found to be of critical use in the structure determination, assuming that the collective dipole moment and polarizability is mainly determined by the dipole-induced–dipole interaction effect.

Two-dimensional vibrational spectroscopy. IV. Relationship between through-space vibrational coupling and intermolecular distance

By means of the ab initio calculation, the second-order nonlinear derivatives of the dipole moment and polarizability of a dimer, CO⋯HCl, with respect to the two, CO and HCl, stretching modes are found to be inversely proportional to r3, where r is the intermolecular distance. The observed r-dependencies are interpreted by taking into account the dipole–induced-dipole interaction. Thus, it is shown that the intermolecular distance between two vibrational chromophores can be estimated by quantitatively examining the cross-peak intensity in a given 2D (two dimensional) vibrational spectrum.