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A previously developed semiclassical theory of nonadiabatic energy transfer is used to analyze electronic excitation and quenching in three-dimensional atomic collisions. The predicted transition probabilities, cross sections, and rate coefficients are compared with the quantum scattering calculations for O + O and N + N, for the same interaction potentials and nonadiabatic coupling, and with the experimental data where available. The theory predictions are in very good agreement with quantum scattering, at the conditions when the energy transfer is dominated by a single pair of adiabatic potentials. Closed-form analytic expressions for the cross sections and rate coefficients are obtained, for both the strongly and weakly coupled cases. The results quantify and illustrate the effect of the interaction potentials and their coupling on the energy transfer. The analytic cross sections and rate coefficients are in good agreement with the numerical predictions. The same approach has been used to predict the rate coefficients of electronic excitation and quenching in collisions of N + O atoms. The fidelity of these predictions may be improved considerably if accurate potentials for the excited electronic states of N + O and their coupling are available. The applicability of the semiclassical theory for the prediction of the rates of heavy particle impact excitation in atom–molecule collisions is discussed. [ABSTRACT FROM AUTHOR]

The rate constants of elementary processes in the atom–diatom system O (3 P) + H 2 (v) , including the processes of vibrational relaxation and dissociation, were studied using the quasiclassical trajectory method. All calculations were carried out along the ground potential energy surface (PES) 3 A ″ that was approximated by a neural network. Approximation data were obtained using ab initio quantum chemistry methods at the extended multi-configuration quasi-degenerate second-order perturbation theory XMCQDPT2 in a basis set limit. The calculated cross-sections of the reaction channels are in good agreement with the literature data. A complete set of state-to-state rate constants was obtained for the metathesis reaction, the dissociation and relaxation of the H2 molecule upon collision with an O atom. According to these data, Arrhenius approximations over a wide temperature range were obtained for the thermal rate constants of considered processes. Data obtained on the dissociation constants and VT relaxation of vibrationally excited H2 molecules can be used in constructing kinetic models describing the oxidation of hydrogen at high temperatures or highly nonequilibrium conditions. [ABSTRACT FROM AUTHOR]

The central collision between a neon atom and a dodecahedrane cage has been investigated within the framework of ab initio Hartree-Fock molecular dynamics simulations for various initial velocities of the incident atom. Four scenarios regarding the interaction's outcome have been identified. A reaction channel involving the encapsulation of the projectile inside the molecular cage has been studied for a simulation time of 4.8 ps. The analysis is focused on: the rate of energy exchange between Ne and C20H20, the mechanical oscillation frequencies of the atom and the cage, and also, on the frequency with which the dipole moment changes. The results suggest that inside the molecular cage, neon is a stable atomic vibrator, which oscillates with the highest peak frequency of 16 THz. Furthermore, the same frequency characterizes the dipole moment oscillation, suggesting a strong coupling between the atom and the cage, making the endohedral system suitable for a wide range of applications in nano-electronics. [ABSTRACT FROM AUTHOR]

In response to the need to investigate and create a reliable dataset of spin-orbit coupling matrix elements, we have extended our recent work in which we presented results for the potential energy curves and permanent and transition dipole moments in KRb. This paper presents 190 allowed spin-orbit couplings between 30 singlet and triplet Σ + , Π , and Δ electronic states of the KRb molecule. These results are crucial for accurately interpreting spectroscopic data, especially for the deperturbation analysis challenges. 23 tables and 21 graphs present the L S X , L S Y , and L S Z components of reported spin-orbit couplings. Using the MOLPRO code, we performed MRCI calculations using the large-core pseudopotentials and core polarization potentials with reoptimized cutoff parameters. The spin-orbit parameters of the potassium pseudopotential were deduced and optimized from scratch. The Gaussian basis sets used in our calculations were appropriately selected, augmented, and optimized. We compare some of our data with available theoretical and experimental results. [ABSTRACT FROM AUTHOR]

Energy transfer in inelastic atom-molecule and molecule-molecule collisions can be described theoretically using the quantum-mechanical close-coupling method. Unfortunately, for bimolecular collisions implying heavy colliders and/or for which the potential energy surface has a deep well, the resulting coupled equations become numerically intractable and approximate methods have to be employed. H2O—CO collisions provide an important example for which close-coupling calculations are not feasible. In this paper, we investigate the accuracy of three approximate methods (the coupled states method, the quasi-classical trajectory method, and the statistical adiabatic channel model) to describe inelastic collisions of H2O with CO. We perform scattering calculations on a recent 5D potential energy surface, and we compare the results of the three approximate methods to fully converged close-coupling calculations at energies below 300 cm−1 and at low values of the total angular momentum. We show that the statistical method provides an attractive alternative to fully quantum mechanical close-coupling calculations at low collision energies, while the quasi-classical method is more advantageous at high energies. [ABSTRACT FROM AUTHOR]

The nonadiabatic alignment dynamics of weakly bound molecule-atom complexes, induced by a moderately intense 300 fs nonresonant laser pulse, is calculated by direct numerical solution of the time-dependent Schrödinger equation. Our method propagates the wave function according to the coupled channel equations for the complex, which can be done in a very efficient and stable manner out to large times. We present results for two van der Waal complexes, CS2-He and HCCH-He, as respective examples of linear molecules with large and small moments of inertia. Our main result is that at intensities typical of nonadiabatic alignment experiments, these complexes rapidly dissociate. In the case of the CS2-He complex, the ensuing rotational dynamics resembles that of isolated molecules, whereas for the HCCH-He complex, the detachment of the He atom severely perturbs and essentially quenches the subsequent rotational motion. At intensities of the laser pulse ≤ 2.0 x 1012 W/cm², it is shown that the molecule-He complex can rotate and align without breaking apart. We discuss the implications of our findings for recent experiments on iodine molecules solvated in helium nanodroplets. [ABSTRACT FROM AUTHOR]

We investigate nonsequential double ionization (NSDI) of molecules by few-cycle laser pulses at the laser intensity of 1.2-1.5 × 1014 W/cm² using the classical ensemble model. The same double-line structure as the lower intensity (1.0 × 1014 W/cm²) is also observed in the correlated electron momentum spectra for 1.2-1.4 × 1014 W/cm². However, in contrast to the lower intensity where NSDI proceeds only through the recollision-induced double excitation with subsequent ionization (RDESI) mechanism, here, the recollision-induced excitation with subsequent ionization (RESI) mechanism has a more significant contribution to NSDI. This indicates that RDESI is not necessary for the formation of the double-line structure and RESI can give rise to the same type of structure independently. Furthermore, we explore the ultrafast dynamics underlying the formation of the double-line structure in RESI. [ABSTRACT FROM AUTHOR]

We use classical trajectory calculations to study the effects of the interaction strength and the geometry of rigid polyatomic molecules on the formation of long-lived collision complexes at low collision energies. We first compare the results of the calculations for collisions of benzene molecules with rare gas atoms He, Ne, Ar, Kr, and Xe. The comparison illustrates that the mean lifetimes of the collision complexes increase monotonically with the strength of the atom-molecule interaction. We then compare the results of the atom-benzene calculations with those for benzene-benzene collisions. The comparison illustrates that the mean lifetimes of the benzene-benzene collision complexes are significantly reduced due to non-ergodic effects prohibiting the molecules from sampling the entire configuration space. We find that the thermally averaged lifetimes of the benzene-benzene collisions are much shorter than those for Xe with benzene and similar to those for Ne with benzene. [ABSTRACT FROM AUTHOR]

The promising field of mechanochemistry suffers from a general lack of understanding of the distribution and propagation of force in a stretched molecule, which limits its applicability up to the present day. In this article, we introduce the JEDI (Judgement of Energy DIstribution) analysis, which is the first quantum chemical method that provides a quantitative understanding of the distribution of mechanical stress energy among all degrees of freedom in a molecule. The method is carried out on the basis of static or dynamic calculations under the influence of an external force and makes use of a Hessian matrix in redundant internal coordinates (bond lengths, bond angles, and dihedral angles), so that all relevant degrees of freedom of a molecule are included and mechanochemical processes can be interpreted in a chemically intuitive way. The JEDI method is characterized by its modest computational effort, with the calculation of the Hessian being the rate-determining step, and delivers, except for the harmonic approximation, exact ab initio results.We apply the JEDI analysis to several example molecules in both static quantum chemical calculations and Born-Oppenheimer Molecular Dynamics simulations in which molecules are subject to an external force, thus studying not only the distribution and the propagation of strain in mechanically deformed systems, but also gaining valuable insights into the mechanochemically induced isomerization of trans-3,4-dimethylcyclobutene to trans,trans-2,4-hexadiene. The JEDI analysis can potentially be used in the discussion of sonochemical reactions, molecular motors, mechanophores, and photoswitches as well as in the development of molecular force probes. [ABSTRACT FROM AUTHOR]

Ultracold single molecules have wide-ranging potential applications, such as ultracold chemistry, precision measurements, quantum simulation, and quantum computation. However, given the difficulty of achieving full control of a complex atom-molecule system, the coherent formation of single molecules remains a challenge. Here, we report an alternative route to coherently bind two atoms into a weakly bound molecule at megahertz levels by coupling atomic spins to their two-body relative motion in a strongly focused laser with inherent polarization gradients. The coherent nature is demonstrated by long-lived atom-molecule Rabi oscillations. We further manipulate the motional levels of the molecules and measure the binding energy precisely. This work opens the door to full control of all degrees of freedom in atom-molecule systems. [ABSTRACT FROM AUTHOR]

Trapping of atoms and molecules in electrostatic, magnetic and optical traps has enabled studying atomic and molecular interactions on a timescale of many seconds, allowing observations of ultra-cold collisions and reactions. Here we report the first magnetic deceleration and trapping of neutral carbon atoms in a static magnetic trap. When co-trapping the carbon atoms with oxygen molecules in a superconducting trap, the carbon signal decays in a non-exponential manner, consistent with the decay model describing losses resulting from atom-molecule collisions. Our findings pave the way to studying both elastic and inelastic collisions of species that cannot be laser cooled, and specifically may facilitate the observation of reactions at low temperatures, such as C + O2 → CO + O, which is important in interstellar chemistry. [ABSTRACT FROM AUTHOR]

The effect of the O2/Ar component ratio in the CHF3 + O2 + Ar mixture on the electrical parameters of the plasma, kinetics of active particles, and their stationary concentrations under the high-frequency (13.56 MHz) induction discharge is investigated. Using jointly the plasma diagnostics and simulation techniques, (i) features of the plasma composition in the oxygen-free system CHF3 + Ar are found, (ii) the effect of oxygen on the stationary concentrations of active particles is established via the kinetics of processes under the electron impact and the reaction of the atom–molecule interaction, and (iii) a simulation analysis of the kinetics of heterogeneous processes (etching, polymerization, and destruction of a polymer film), which determine the etching mode and output characteristics, is carried out. [ABSTRACT FROM AUTHOR]

We have measured vibrational population of H2 and D2 molecules produced by atom (H or D) recombination on tungsten and copper material. The vibrational spectroscopy, based on the properties of dissociative electron attachment to hydrogen molecule, was used. The vibrationally excited molecules were produced by atom recombination in a cell where the studied sample is exposed to hydrogen atoms, from hot tungsten filament. Vibrational populations were obtained for the studied materials, which can be well described by the Boltzmann distribution, with specific vibrational temperatures for each material. The experimentally obtained vibrational populations for copper approximately agree with the theoretical predictions, whereas the experimentally obtained vibrational temperature for tungsten is higher and thus showing a considerable overpopulation of highly excited vibrational states than predicted. We propose that the origin of this higher excitation is related to the existence of high hydrogen surface coverage on tungsten, where hydrogen is occupying binding sites with different desorption energies. In order to obtain an insight into the recombination mechanism with more than one binding site per unit cell, a Monte Carlo simulation was performed, where it was assumed that the main production of molecules proceeds through the hot-atom recombination with an adsorbed atom. The results show that the recombination proceeds mainly through the weak binding sites, once they are occupied. [ABSTRACT FROM AUTHOR]

Theory of long-range interactions between an atom in its ground S state and a linear molecule in a degenerate state with a nonzero projection of the electronic orbital angular momentum is presented. It is shown how the long-range coefficients can be related to the first and second-order molecular properties. The expressions for the long-range coefficients are written in terms of all components of the static and dynamic multipole polarizability tensor, including the nondiagonal terms connecting states with the opposite projection of the electronic orbital angular momentum. It is also shown that for the interactions of molecules in excited states that are connected to the ground state by multipolar transition moments additional terms in the long-range induction energy appear. All these theoretical developments are illustrated with the numerical results for systems of interest for the sympathetic cooling experiments: interactions of the ground state Rb(2S) atom with CO(3Π), OH(2Π), NH(1Δ), and CH(2Π) and of the ground state Li(2S) atom with CH(2Π). [ABSTRACT FROM AUTHOR]

A simple method for computing accurate density-dependent dispersion coefficients is presented. The dispersion coefficients are modeled by a generalized gradient-type approximation to Becke and Johnson's exchange hole dipole moment formalism. Our most cost-effective variant, based on a disjoint description of atoms in a molecule, gives mean absolute errors in the C6 coefficients for 90 complexes below 10%. The inclusion of the missing long-range van der Waals interactions in density functionals using the derived coefficients in a pair wise correction leads to highly accurate typical noncovalent interaction energies. [ABSTRACT FROM AUTHOR]

Collision properties of atoms and molecules in low temperature gases can be controlled by applying an external magnetic or electric field. The external field shifts the energy levels of the colliding particles, which gives rise to Feshbach resonances modifying the scattering cross sections. The resonances occur at particular magnitudes of the external field, where a bound state of the collision complex is degenerate with a scattering state. The positions of the resonances in the external field are usually identified by computing either the scattering cross sections or the bound states of the collision complex as functions of the external field magnitude. We propose a more efficient method for locating Feshbach resonances that requires neither of these computations. In particular, we show that the positions of Feshbach resonances can be identified by computing the log-derivative of the total wave function in a classically allowed region as a function of the external field strength. This procedure is particularly useful for locating narrow Feshbach resonances that may be hard to identify with the other methods. [ABSTRACT FROM AUTHOR]

Steric effect for the XeBr* (B, C) formation in the oriented Xe*(3P2, MJ=2)+oriented CF3Br reaction has been observed as a function of the mutual configuration between the molecular orientation and the atomic orientation in the collision frame. Molecular steric opacity function has been determined as a function of the atomic orbital alignment (LZ′) in the collision frame. The LZ′ selectivity in the molecular steric opacity function is different between the XeBr* (B, C) channels: For the XeBr* (C) channel, the LZ′=0 alignment is favorable at the molecular axis direction and the |LZ′|=1 alignment is favorable at the sideway direction, whereas for the XeBr* (B) channel, the LZ′=0 alignment is favorable at the sideway direction and the |LZ′|=1 alignment is favorable at the molecular axis direction. However, the shape of the steric opacity function for the XeBr* (B) channel at the LZ′=0 (and |LZ′|=1) alignment is similar to that for the XeBr* (C) channel at the |LZ′|=1 (and LZ′=0) alignment, respectively: A large molecular orientation dependence (i.e., the largest reactivity at the Br-end with the small molecular alignment dependence) is recognized for the XeBr* (B) channel at the LZ′=0 alignment and for the XeBr* (C) channel at the |LZ′|=1 alignment, whereas a large molecular alignment dependence (i.e., the largest reactivity at the Br-end with the poor reactivity at the sideway) is recognized for the XeBr* (B) channel at the |LZ′|=1 alignment and for the XeBr* (C) channel at the LZ′=0 alignment. We propose the indirect mechanism for the dark channels (Xe+Br+CF3) via the back-electron transfer from the CF3 segment (or dissociating CF3...Br-) to Xe+ as the origin of the significant molecular alignment dependence in the molecular steric opacity function. [ABSTRACT FROM AUTHOR]

Following upon our recent work on vector correlations in the Ar–NO collisions [Lemeshko and Friedrich, Phys. Chem. Chem. Phys. 12, 1038 (2010)], we compare model results with close-coupling calculations for a range of channels and collision energies for the He–NO system. The striking agreement between the model and exact polarization moments indicates that the stereodynamics of rotationally inelastic atom-molecule collisions at thermal energies is governed by diffraction of matter waves from a two-dimensional repulsive core of the atom-molecule potential. Furthermore, the model polarization moments characterizing the He–NO, He–O2, He–OH, and He–CaH stereodynamics are found to coalesce into a single, distinctive pattern, which can serve as a “fingerprint” to identify diffraction-driven stereodynamics in future work. [ABSTRACT FROM AUTHOR]

The interaction of individual Al atoms with water molecules has been studied from the point of view of the energy by means of ab initio and DFT calculations in order to find the pathways for the generation of HAlOH·(H2O)n or AlOH·(H2O)n+H. The potential energy surface of the Al(H2O)n+1 (n=0–3) systems has been explored for local minima and the relevant saddle points. The interaction of Al and several water molecules tends to produce low-lying local minima in which (for n=2–3) Al is “inserted” into relatively compact structures of water molecules, so typically a ring is formed containing an Al·OH2 moiety. Isomerization of such moiety into HAlOH·(H2O)n may take place through saddle points of the “relay” type; however those saddle points lie very close to Al·OH2·(H2O)n-1+H2O, which means that such isomerization process has to compete with a water-elimination process. Larger systems Al(H2O)n+1 (n=4–7) have also been computed by means of a DFT method, as a first step to predict the behavior of isolated Al atoms in even larger clusters or in the bulk. Finally, an effective fragment potential method has been employed to simulate those large clusters together with a polarizable continuum model to take into account the effect of the bulk. Our results suggest that the reaction should take place in inert matrices and in the bulk. We also conclude that HAlOH·(H2O)n and AlOH·(H2O)n could be the intermediates involved in the generation of hydrogen by the interaction of Al atoms with water, so their production would be the critical step of such process. [ABSTRACT FROM AUTHOR]

The coherence of graphene layers on Ru(0001) over extended distances has been employed to identify fcc and hcp regions of the associated moiré superstructure. These findings can be used as a straightforward method to discriminate between fcc and hcp hollow sites of Ru(0001). Our approach thereby makes use of the “magnifying lens” characteristics of the graphene/Ru(0001) overlayer and its coherence across several monatomic steps of the substrate. We demonstrate that the individual regions of the graphene/Ru(0001) overlayer exhibit pronounced variations in interaction strengths with deposited metal atoms. Specifically, Pt clusters have been grown at 140–180 K and they are found to organize in a well-ordered periodic array defined by the moiré superlattice. Their preferred location within the graphene/Ru(0001) moiré unit cell is identified to be the fcc region. [ABSTRACT FROM AUTHOR]

Connectivity in the potential energy landscape of a binary Lennard-Jones system can be characterized at the level of cage-breaking. We calculate the number of cage-breaking routes from a given local minimum and determine the branching probabilities at different temperatures, along with correlation factors that represent the repeated reversals of cage-breaking events. The number of reversals increases at lower temperatures and for more fragile systems, while the number of accessible connections decreases. We therefore associate changes in connectivity with super-Arrhenius behavior. Reversals in minimum-to-minimum transitions are common, but often correspond to “non-cage-breaking” processes. We demonstrate that the average waiting time within a minimum shows simple exponential behavior with decreasing temperature. To describe the long-term behavior of the system, we consider reversals and connectivity in terms of the “cage-breaking” processes that are pertinent to diffusion [V. K. de Souza and D. J. Wales, J. Chem. Phys. 129, 164507 (2008)]. These cage-breaking events can be modeled by a correlated random walk. Thus, a full correlation factor can be calculated using short simulations that extend up to two cage-breaking events. [ABSTRACT FROM AUTHOR]

Dynamic restructuring of the Ag(111) surface occurs during the reaction of sulfur dioxide with Ag(111)-p(4×4)-O at 300 K, resulting in the incorporation of added silver atoms into the unit cells of both adsorbed sulfite and sulfate. This result clearly demonstrates that incorporation of metal atoms into the structures of adsorbates and reaction intermediates is not restricted to more open, higher free energy single crystal planes. These observations indicate that the participation of added metal atoms must be considered in the theoretical treatment of metal catalyzed reactions. [ABSTRACT FROM AUTHOR]

Experimental crossed-beam studies carried out previously have indicated that the dynamics of the Rydberg-atom-molecule reaction H*+D2→D*+HD are very similar to those of the corresponding ion-molecule reaction H++D2→D++HD. The equivalence of the cross sections for these related systems would open up a new approach to the experimental study of ion-molecule reactions. However, a recent experimental and theoretical study has brought to light some important qualitative differences between the Rydberg-atom reaction and the ion-molecule reaction; in particular, the experimental cross section for the Rydberg-atom reaction exhibits a higher degree of forward-backward scattering asymmetry than predicted by a quasiclassical trajectory study of the ion-molecule reaction. In this paper, the authors consider the dynamics of the Rydberg-electron over the course of a reactive collision and the implications of these dynamics for the Rydberg-atom-molecule crossed-beam experiment. Using an approach based on perturbation theory, they estimate the attenuation of the experimental signal due to the Rydberg-electron dynamics as a function of the scattering angle. They show that at least part of the experimental asymmetry can be ascribed to this angle dependent attenuation. Their results offer general insight into the practical aspects of the experimental study of ion-molecule reactions by means of their Rydberg-atom counterparts. [ABSTRACT FROM AUTHOR]

The energy transfer dynamics between highly vibrationally excited azulene molecules (37 582 cm-1 internal energy) and Ar atoms in a series of collision energies (200, 492, 747, and 983 cm-1) was studied using a crossed-beam apparatus along with time-sliced velocity map ion imaging techniques. The angular resolved collisional energy-transfer probability distribution functions were measured directly from the scattering results of highly vibrationally excited azulene. Direct T-V/R energy transfer was found to be quite efficient. In some instances, nearly all of the translational energy is transferred to vibrational/rotational energy. On the other hand, only a small fraction of vibrational energy is converted to translational energy (V-T). Significant amount of energy transfer from vibration to translation was observed at large collision energies in backward and sideway directions. The ratios of total cross sections between T-V/R and V-T increases as collision energy increases. Formation of azulene-argon complexes during the collision was observed at low enough collision energies. The complexes make only minor contributions to the measured translational to vibrational/rotational (T-V/R) energy transfer. [ABSTRACT FROM AUTHOR]

Inelastic scattering matrix elements for the nonadiabatic collision B(2P1/2)+H2(1Σg+,j)↔B(2P3/2)+H2(1Σg+,j′) are calculated using the time dependent channel packet method (CPM). The calculation employs 1 2A′, 2 2A′, and 1 2A″ adiabatic electronic potential energy surfaces determined by numerical computation at the multireference configuration-interaction level [M. H. Alexander, J. Chem. Phys. 99, 6041 (1993)]. The 1 2A′ and 2 2A′, adiabatic electronic potential energy surfaces are transformed to yield diabatic electronic potential energy surfaces that, when combined with the total B+H2 rotational kinetic energy, yield a set of effective potential energy surfaces [M. H. Alexander et al., J. Chem. Phys. 103, 7956 (1995)]. Within the framework of the CPM, the number of effective potential energy surfaces used for the scattering matrix calculation is then determined by the size of the angular momentum basis used as a representation. Twenty basis vectors are employed for these calculations, and the corresponding effective potential energy surfaces are identified in the asymptotic limit by the H2 rotor quantum numbers j=0, 2, 4, 6 and B electronic states 2Pja, ja=1/2, 3/2. Scattering matrix elements are obtained from the Fourier transform of the correlation function between channel packets evolving in time on these effective potential energy surfaces. For these calculations the H2 bond length is constrained to a constant value of req=1.402 a.u. and state to state scattering matrix elements corresponding to a total angular momentum of J=1/2 are discussed for j=0↔j′=0,2,4 and 2P1/2↔2P1/2, 2P3/2 over a range of total energy between 0.0 and 0.01 a.u. [ABSTRACT FROM AUTHOR]

We report the first experimental demonstration of vibrational mode-dependent enhancement in photodissociation and photoionization of a seven atom molecule, methylamine (CH3NH2). The fundamental C-H stretches and the overtones or combinations of CH3 bends were prepared via stimulated Raman excitation (SRE) prior to their 243.135 nm one-photon dissociation or two-photon ionization. The photodissociation or photoionization of the vibrationally excited molecules was achieved via 10 ns delayed or temporally overlapping SRE and UV pulses, respectively. It is shown that bending modes are more effective than stretches in promoting photodissociation and photoionization, since their UV excitation is favored by larger Franck Condon factors. This behavior provides clear evidence for vibrational mode-dependence in a relatively large molecule with a torsional degree of freedom, indicating that these modes survive intramolecular vibrational redistribution on a time scale considerably longer than hitherto inferred from previous studies. [ABSTRACT FROM AUTHOR]

This paper presents the methodology to generate beams of ions in single quantum states for bimolecular ion-molecule reaction dynamics studies using pulsed field ionization (PFI) of atoms or molecules in high-n Rydberg states produced by vacuum ultraviolet (VUV) synchrotron or laser photoexcitation. Employing the pseudocontinuum high-resolution VUV synchrotron radiation at the Advanced Light Source as the photoionization source, PFI photoions (PFI-PIs) in selected rovibrational states have been generated for ion-molecule reaction studies using a fast-ion gate to pass the PFI-PIs at a fixed delay with respect to the detection of the PFI photoelectrons (PFI-PEs). The fast ion gate provided by a novel interleaved comb wire gate lens is the key for achieving the optimal signal-to-noise ratio in state-selected ion-molecule collision studies using the VUV synchrotron based PFI-PE secondary ion coincidence (PFI-PESICO) method. The most recent development of the VUV laser PFI-PI scheme for state-selected ion-molecule collision studies is also described. Absolute integral cross sections for state-selected H2+ ions ranging from v+=0 to 17 in collisions with Ar, Ne, and He at controlled translational energies have been obtained by employing the VUV synchrotron based PFI-PESICO scheme. The comparison between PFI-PESICO cross sections for the H2+(HD+)+Ne and H2+(HD+)+He proton-transfer reactions and theoretical cross sections based on quasiclassical trajectory (QCT) calculations and three-dimensional quantum scattering calculations performed on the most recently available ab initio potential energy surfaces is highlighted. In both reaction systems, quantum scattering resonances enhance the integral cross sections significantly above QCT predictions at low translational and vibrational energies. At higher energies, the agreement between experiment and quasiclassical theory is very good. The profile and magnitude of the kinetic energy dependence of the absolute integral cross sections for the H2+(v+=0–2,N+=1)+He proton-transfer reaction unambiguously show that the inclusion of Coriolis coupling is important in quantum dynamics scattering calculations of ion-molecule collisions. [ABSTRACT FROM AUTHOR]

N-methylacetamide (NMA) is a very interesting compound and often serves as a model of the peptide bond. The interaction between NMA and water provides a convenient prototype for the solvation of the peptides in aqueous solutions. Here we present NMA-water potential model based on atom-bond electronegativity equalization method fused into molecular mechanics (ABEEM/MM) that is to take ABEEM charges of all atoms, bonds, and lone-pair electrons of NMA and water molecules into the electrostatic interaction term in molecular mechanics. The model has the following characters: (1)it allows the charges in system to fluctuate responding to the ambient environment; (2) for two major types of intermolecular hydrogen bonds, which are the hydrogen bond forming between the lone-pair electron on amide oxygen and the water hydrogen, and the one forming between the lone-pair electron on water oxygen and the amide hydrogen, we take special treatments in describing the electrostatic interaction by the use of the parameters klpO==,H and klpO–,HN–, respectively. The newly constructed potential model based on ABEEM/MM is first applied to amide-water clusters and reproduces gas-phase state properties of NMA(H2O)n (n=1–3) including optimal structures, dipole moments, ABEEM charge distributions, energy difference of the isolated trans- and cis-NMA, interaction energies, hydrogen bonding cooperative effects, and so on, whose results show the good agreement with those measured by available experiments and calculated by ab initio methods. In order to further test the reasonableness of this model and the correctness and transferability of the parameters, many static properties of the larger NMA-water complexes NMA(H2O)n (n=4–6) are also studied including optimal structures and interaction energies. The results also show fair consistency with those of our quantum chemistry calculations. [ABSTRACT FROM AUTHOR]

The room-temperature termolecular rate constants, k0, for the Mu+CO+M≤=≥MuCO+M (M=He, N2, Ar) recombination reaction have been measured by the μSR technique, and are reported for moderator gas pressures of up to ∼200 bar (densities <=0.4×1022 molec cm-3). The experimental relaxation rates reveal an unusual signature, in being dominated by the electron spin-rotation interaction in the MuCO· radical that is formed in the addition step. In N2 moderator, k0=1.2±0.1×10-34 cm6 s-1, only about 30% higher than found in Ar or He. The experimental results are compared with theoretical calculations carried out on the Werner-Keller-Schinke (WKS) surface [Keller et al., J. Chem. Phys. 105, 4983 (1996)], within the framework of the isolated resonance model (IRM). The positions and lifetimes of resonance states are obtained by solving the complex Hamiltonian for the nonrotating MuCO system, using an L2 method, with an absorbing potential in the asymptotic region. Accurate values of the vibrational bound and resonance states of MuCO reveal unprecedented isotope effects in comparisons with HCO, due to the remarkable effect of replacing H by the very light Mu atom (mMu≈1/9mH). Due to its pronounced zero-point energy shift, there are only two (J=0) bound states in MuCO. Contributions from nonzero J states to the termolecular rate constants are evaluated through the J-shifting approximation, with rotational constants evaluated at the potential minimum. The value of the important A constant (181 cm-1) used in this approximation was supported by accurate J=K=1 calculations, from which A=180 cm-1 was obtained by numerical evaluation. The calculations presented here, with a “weak collision factor” βc=0.001, indicative of the very sparse density of MuCO states, give a very good account of both the magnitude and pressure dependence of the experimental rates, but only when the fact that the two initially bound (J=0) states become resonances for J>0 is taken into account. This is the first time in IRM calculations of atom-molecule recombination reactions where J≠0 states have proven to be so important, thus providing a truly unique test of quantum rate theory. [ABSTRACT FROM AUTHOR]

We present an improved procedure on the approach to determine the stability of polystyrene spheres at microscopic particle levels by means of artificially induced particle collisions with the aid of optical tweezers [J. Chem. Phys. 119, 2399 (2003)]. The basic consideration on this new development is that the major contribution to the sticking probability for a particle pair caught into the optical trap for a short period is from its single collision; therefore, if the trapping duration for the pair is taken to be short, the accumulated sticking probability will be a good approximation for the single collision. The experimental procedure associated with this approximation does not resort to exactly controlling the short trapping duration or request the trapping duration correction as previously reported, and therefore it is more practical and applicable for a broader range of the stability ratio. The experimental results under different electrolyte concentrations by the new procedure are consistent with those from the turbidity measurements. [ABSTRACT FROM AUTHOR]

We report differential scattering experiments on the laser excitation of Na+M collision pairs with M=N2, CO, C2H2, and CO2. The collision event is probed by the laser polarization revealing geometric and electronic properties of the collision pair. The experimental data are compared to the results of a Monte Carlo trajectory simulation using ab initio quantum chemical data.© 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A theory for quantum-mechanical calculations of cross sections for atom-molecule and molecular collisions in a magnetic field is presented. The formalism is based on the representation of the wave function as an expansion in a fully uncoupled space-fixed basis. The systems considered include [sup 1]S-atom–[sup 2]Σ-molecule, [sup 1]S-atom–[sup 3]Σ-molecule, [sup 2]Σ-molecule–[sup 2]Σ-molecule, and [sup 3]Σ-molecule–[sup 3]Σ-molecule. The theory is used to elucidate the mechanisms for collisionally induced spin depolarization. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Graphical abstract Influence of cations and anions on the formation of gamma polar phase in polyvinylidene fluoride. Highlights • Polymer/Ionic liquids system can be treated as a ternary system. • The effect of the chemical nature of the cation and the anion may interfere on the crystalline phase formation of the PVDF polymer. • The acidity Brønsted difference of the ionic liquids result in different polarities in the main polymer chain. • A nanoestruturação por ILS promove RAF e MAF. • The existence of ILs in the RAF acts as an obstacle for the growth of larger structures. Abstract The ability of different microstructures from ionic liquids (ILs) governed by anions and cations has been a source of curiosity for composite systems. In this present study, the structural behavior of polyvinylidene fluoride (PVDF) mixed with phosphonium- and imidazolium-based ionic liquids (1 wt%) combined with different counter anions was investigated. The effect of the chemical nature of the cation and the anion on the resulting polar crystals was evaluated. Thus, the formation of polar phase after IL incorporation was highlighted with morphologic observation of spherulites of low-birefringence using polarizing optical (POM) and atomic force microscopies (AFM), and their crystalline structures were confirmed by infrared spectroscopy (FTIR) and Wide-angle X-ray diffraction (WAXS). However, the enhancement of polar γ-phase crystallization was mainly observed in presence of phosphonium-based ILs suggesting that the nanostructuration mechanism were amply dependent on the interacting abilities of ILs in PVDF matrix. In addition, we have also demonstrated that the presence of ILs within the crystalline lamellae, characterized by SAXS and DMA, oriented the chains allowing the formation of rigid amorphous fraction (RAF). For this reason, we proposed that the depression of spherulites size was due to the existence of ILs in the RAF acting as obstacle for the growth of larger structures. Finally, these different changes in the microscopic level structure bestowed a rather unique property which modified the mechanical performance of the polymer materials, especially the ability to sustain large deformation. [ABSTRACT FROM AUTHOR]

The article presents a study which reveals that metamaterials can fundamentally modify dipole-dipole interactions between closely spaced atoms and molecules despite large physical separation between interacting quantum emitters. It demonstrate two orders of magnitude increase in the interactions at intermediate field distances and observe distance scaling law consistent with super-Coulombic interaction theory. It concludes that the interactions can be controlled using hyperbolic metamaterials.

Collision Induced Exchange cross-sections for the Zeldovich reaction N 2 + O ⇌ NO + N for high energy atom-molecular collisions are calculated using the Quasi-Classical Trajectory method. The dynamical study of O 2 +N collision is conducted using the 2 A ′ and 4 A ′ NO 2 PESs reported Sayos et al. Cross-sections for the reverse exchange reaction involving NO + O collisions are also calculated and reported. In addition to these exchange reactions, Collision Induced Dissociation cross-sections for dissociation of molecules are also published. Overall, a cross-section database for four important atom-molecule reactions of the air chemistry is provided as supplementary material with this paper. [ABSTRACT FROM AUTHOR]

The interatomic interactions in a diatomic molecule can be fairly modeled by the Morse potential. Short range interactions of the molecule with the neighboring environment can be analyzed by modifying this potential by delta functions. Energy spectra and radial matrix elements have been calculated using an accurate nine-point finite-difference method for such an interacting homonuclear diatomic molecule. The effect of the strength and position of a single delta function interaction on the alignment of this molecule has been studied. The dependence of alignment on the strength of applied field has also been analyzed. [ABSTRACT FROM AUTHOR]

Ab initio quantum chemistry calculations are performed for the mixed alkali triatomic system. Global minima of the ground and first excited doublet states of the trimer are found and Born-Oppenheimer potential energy surfaces of the Li atom interacting with the LiCs molecule were calculated for these states. The lithium atom is placed at various distances and bond angles from the lithium-caesium dimer. Three-body nonadditive forces of the Li 2 Cs molecule in the global minimum are investigated. Dimer-atom interactions are found to be strongly attractive and may be important in the experiments, particularly involving cold alkali polar dimers. [ABSTRACT FROM AUTHOR]