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The superoxide disproportionation reaction is a key step in the chemistry of aprotic metal oxygen batteries that controls the peroxide formation upon discharge and opens the way for singlet oxygen release. Here we clarify the energy landscape of the disproportionation of superoxide in aprotic media catalyzed by group 1A cations. Our analysis is based on ab initio multireference computational methods and unveils the competition between the expected reactive path leading to peroxide and an unexpected reaction channel that involves the reduction of the alkaline ion. Both channels lead to the release of triplet and singlet O2. The existence of this reduction channel not only facilitates singlet oxygen release but leads to a reactive neutral solvated species that can onset parasitic chemistries due to their well-known reducing properties. Overall, we show that the application of moderate overpotentials makes both these channels accessible in aprotic batteries.

We use a multiconfigurational and correlated ab initio method to investigate the fundamental electronic properties of the peroxide MO2- (M = Li and Na) trimer to provide new insights into the rather complex chemistry of aprotic metal-O2 batteries. These electrochemical systems are largely based on the electronic properties of superoxide and peroxide of alkali metals. The two compounds differ by stoichiometry: the superoxide is characterized by a M+O2- formula, while the peroxide is characterized by [M+]2O22-. We show here that both the peroxide and superoxide states necessarily coexist in the MO2- trimer and that they correspond to their different electronic states. The energetic prevalence of either one or the other and the range of their coexistence over a subset of the MO2- nuclear configurations is calculated and described via a high-level multiconfigurational approach.

The initial deactivation pathways of gaseous 2-nitrophenol excited at 268 nm were investigated by time-resolved photoelectron spectroscopy (TRPES) with femtosecond-VUV light, produced by a monochromatized high harmonic generation source. TRPES allowed us to obtain new, valuable experimental information about the ultrafast excited-state dynamics of 2-nitrophenol in the gas phase. In accord with recent ab initio on-The-fly nonadiabatic molecular dynamic simulations, our results validate the occurrence of an ultrafast intersystem crossing leading to an intermediate state that decays on a subpicosecond time scale with a branched mechanisms. Two decay pathways are experimentally observed. One probably involves proton transfer, leading to the most stable triplet aci-form of 2-nitrophenol; the second pathway may involve OH rotation. We propose that following intersystem crossing, an ultrafast fragmentation channel leading to OH or HONO loss could also be operative.

Multivalent aprotic metal–oxygen batteries are a novel concept in the applied electrochemistry field. These systems are variants of the so-called Li–air batteries and up to present are in their research infancy. The superoxide disproportionation reaction is a crucial step for the operation of any metal–oxygen redox system using aprotic solvents: in the best scenario, disproportionation leads to peroxide formation while in the worse one it releases singlet molecular oxygen. In this work we address the fundamental thermodynamics of such reaction for alkali (Li, Na and K) and alkaline earth (Be, Mg and Ca) metal–O2 systems using multiconfigurational ab initio methods. Our aim is to draw a comprehensive description of the disproportionation reaction from superoxides to peroxides and to provide the thermodynamic likelihood of the pathways to singlet oxygen release.

We present a computational analysis of the complex proton-transfer processes in two protic ionic liquids based on phosphorylated amino acid anions. The structure and the short time dynamics have been analyzed via ab initio and semi-empirical molecular dynamics. Given the presence of mobile protons on the side chain, such ionic liquids may represent a viable prototype of highly conductive ionic mediums. The results of our simulations are not entirely satisfactory in this respect. Our results indicate that conduction in these liquids may be limited due to a quick quenching of the proton-transfer processes. In particular, we have found that, while proton migration does occur on very short timescales, the amino groups act as proton scavengers preventing an efficient proton migration. Despite their limits as conductive mediums, we show that these ionic liquids possess an unconventional microscopic structure, where the anionic component is made by amino acid anions that the aforementioned proton transfer has transformed into zwitterionic isomers. This unusual chemical structure is relevant because of the recent use of amino acid-based ionic liquids, such as CO2 absorbent.

Nanosized clusters of protic ionic liquids are investigated using ab-initio DFT methods to understand their propensity to remain ionic. Protic ionic liquids are based on acid/base pairs and are ionic because of proton transfer from the acid to the base. Two prototypical ionic liquids based on triethylamine and two acids of different strengths are used here to trace the tendency toward proton transfer when the system size is gradually increased from an isolated pair of molecules to cluster of several pairs. We have found that the compounds based on the weak acid shows the existence of a well-defined minimal size that represents the threshold for the onset of ionization phenomena.

Open in a separate window The local structure of a series of homologous protic ionic liquids (PILs) is investigated using ab initio computations and ab initio-based molecular dynamics. The purpose of this work is to show that in PILs the network of hydrogen bonds may promote like-charge clustering between anionic species. We correlate the theoretical evidence of this possibility with viscosity experimental data. The homologous series of liquids is obtained by coupling choline with amino acid anions and varying the side chain. We find that the frictional properties of the liquids are clearly connected to the ability of the side chain to establish additional hydrogen bonds (other than the trivial cation–anion interaction). We also show that the large variation of bulk properties along the series of compounds can be explained by assuming that one of the sources of friction in the bulk liquid is the like-charge interaction between anions.

We present an analysis of gas-phase structures of small clusters of n-alkylammonium nitrates (ethyl, propyl, and butyl) together with vibrational Raman spectroscopy of their respective liquid phases. The assignment and interpretation of the resonant frequencies have been performed by comparison with high-quality ab initio (DFT) computations. The theoretical spectra are in excellent agreement with the measured ones and allow the interpretation and assignment of almost all the spectral features. A careful analysis of the vibrational frequencies and of the electronic structure of the compounds has provided additional information on various structural features and on the rather complex hydrogen bonding network that exists in such compounds. A geometric structure of the short-range local arrangement in the bulk phases is also proposed.

We present an analysis of the structure of the monomethylammonium nitrate (MMAN) compound. Vibrational Raman spectroscopy and X-ray powder diffraction have been used to characterize the bulk phases of MMAN, and assignment of the resonant frequencies has been performed by ab initio (DFT) computations on small clusters of the compound. The theoretical spectra are in excellent agreement with the experimental ones and provide a means by which an interpretation of the hydrogen-bonding network that exists in such compound can be analyzed. In particular, we found that the spectrum of one of the solid phases is structurally very similar to that of the liquid. We present experimental evidence for the existence of such phase both from X-ray data and Raman spectra which, in turn, is easily interpreted with a one-to-one correspondence with the ab initio simulation of the small clusters. A geometric structure of the short-range local arrangement in these two bulk phases is therefore proposed.

The fully three-dimensional ground and first electronically excited states of the [LiHHe]+ system were computed with ab initio methods, using a self-consistent field treatment followed by a multi-reference configuration interaction calculation. The topology and reactive pathways of the surfaces are analysed at different configurations extending the understanding of the possible dynamics on these surfaces with respect to previous studies limited to lower dimensionality. The behavior of LiH+ inside or at the surface of a helium droplet is surmised from our findings, along with some suggestions on possible ways with which the different reactive and deexcitation phenomena occurring in this environment could be experimentally detected.

A newly computed potential energy surface, which describes the forces at play between the OH− (X 1Σ+) anionic molecule (treated as a rigid rotor at its equilibrium geometry) and the Rb(2S) atomic gas was obtained from fully ab initio methods, yielding highly correlated electronic wavefunctions for the interacting partners. It is in turn employed to calculate their rotationally quenching collision cross sections at ultralow energies and for different initial rotational states of the molecular anion. The results suggest that these strongly interacting partners are among the most efficient systems in providing very large internal de-excitation rates whenever the collision regime of an ultracold trap can occur for the partners. The collision encounters at such vanishing values of translational energies are seen to be strongly controlled by the behaviour of the real part of the scattering length as a function of the initial rotational state: the latter indicates, in fact, the presence of several virtual states close to the dissociation threshold of the complex.

Rotationally superelastic collisions are computed from quantum dynamical calculations for the two title systems, down to the very low collision energies of interest in cold trap experiments. The results are obtained via ab initio interaction potentials, the one for the MgH-He system being given here for the first time and discussed in details in the present paper. The calculations show marked differences in behaviour for both cooling efficiency rates at vanishing temperatures and individual cross sections between levels, and their origin is related to target structural properties and with specific features of the two potentials.

Ab initio computed interaction forces are employed in order to describe the microsolvation of the A$_2^+(^2\Sigma)$ (A=Li,Na,K) molecular ion in $^4$He clusters of small variable size. The minimum energy structures are obtained by performing energy minimization based on a genetic algorithm approach. The symmetry features of the collocation of solvent adatoms around the dimeric cation are analyzed in detail, showing that the selective growth of small clusters around the two sides of the ion during the solvation process is a feature common to all three dopants.

An ab initio computed potential energy surface is employed to evaluate the interaction of the OH+(3Σ -) molecule with 4He(1S) atom and an analytic fitting of the raw points is directly employed in quantum scattering calculations at ultralow collision energies. The Hund's case (b) chosen to handle the spin-rotation coupling allows to extract from the numerous inelastic cross sections the relative importance of pure “spin flip" vis-a- vis rotational cooling cross sections. The final rates of all the above processes as a function of the initial |N〉 state are analysed in detail and possible propensity rules are discussed.

Ab initio potentials are computed for alkali metal cationic partners interacting with 4He and an overall many-body potential is constructed for each of the ionic dopants in helium clusters. The structures are then obtained via a genetic algorithm approach and results compared with Basin-Hopping Monte Carlo simulations. The classical arrangements are analyzed and quantum effects discussed in comparison with what has been found with Diffusion Monte Carlo calculations. Further corrections to the classical picture by including three-body forces and radial delocalization of the helium adatoms are also considered and their effects analyzed.

The interactions of Rubidium and Cesium atoms with the NH radical at its equilibrium geometry are investigated over several interpartner distances and for a variety of angular orientations of the atoms with respect to the intermolecular bond. Several electronic states are computed at the CASSCF level and the lowest four are analysed in greater detail at the MRCI level in order to finally obtain orientational potential energy surfaces. The evaluation of the involved Franck-Condon factors reveals the possibility of photoassociation mechanisms into bound states of the two complex triatomics and further suggests stable complex configurations in the lowest quartet states from DVR calculations of the J = 0 relevant bound states. The work above exemplifies the recent interests of the theory group in Rome on ultracold dynamics and interaction processes which are also briefly reviewed in the introduction.

We present a study of the solvation of lanthanoid(III) ions in liquid dimethyl sulfoxide (DMSO) using molecular dynamics simulations employing a newly developed polarizable force field. The van der Waals (vdW) parameters were obtained for La(3+) and Lu(3+) (the first and the last in the lanthanoid(III) series) using ab initio data. The parameters of the other ions can be extrapolated based on physical considerations without additional (and costly) quantum chemistry calculations. This extrapolation procedure has been successfully applied to Gd(3+). The outcomes of our simulations turn out to be in agreement with both the experimental data available in the literature and the ab initio results. A small adjustment of the vdW parameters further increases the agreement with experiments and has allowed us to provide structures, geometrical parameters, and coordination numbers. For heavy lanthanoids (Gd and Lu) we obtain clearly an 8-fold coordination, with a distorted square antiprism (SAP) geometry in agreement with EXAFS and XANES experiments; for the La(3+) ion, our force field predicts a mixed situation with both the 8-fold SAP and 9-fold geometry where the SAP structure is capped by a ninth molecule added over one face.

The combination of amino acid anions with the choline cation gives origin to a new and potentially important class of organic ionic liquids that might represent a viable and bio-compatible alternative with respect to the traditional ones. We present here a detailed study of the bulk phase of the prototype system composed of the simplest amino acid (alanine) anion and the choline cation, based on ab initio and classical molecular dynamics. Theoretical findings have been validated by comparing with accurate experimental X-ray diffraction data and infrared spectra. We find that hydrogen bonding (HB) features in these systems are crucial in establishing their local geometric structure. We have also found that these HBs once formed are persistent and that the proton resides exclusively on the choline cation. In addition, we show that a classical force field description for this particular ionic liquid can be accurately performed by using a slightly modified version of the generalized AMBER force field.

Accurate, post-Hartree–Fock calculations have been carried out for a broad range of geometries in order to obtain an extended description of the orientational anisotropy and radial strength of the interaction of OH + and OH - ions with the unit species of a weak quantum solvent as that provided by 4 He droplets. The potential energy surfaces (PES) are obtained for the smallest complex system with one 4 He atom, and the possible role and importance of many-body effects is also investigated. The energetics and shapes of the OH +-4 He and OH --4 He internal bound states are obtained and analyzed in detail.

In the present review we summarize in some detail the ample theoretical literature which has discussed over the last few years the computational treatment of collisionally inelastic processes at ultralow temperatures. The analysis is centred on the ab initio quantum treatment of collisional quenching of ro-vibrational states of simple diatomics, neutral and ionic, polar and homonuclear, interacting with a helium buffer gas. Several specific examples are analysed and their features are linked with both the details of their interaction potential energy surfaces and the special behavior of ultralow energy quantum dynamics. †This work is affectionately dedicated to the late Roger Miller, a brilliant scientist and a dear friend whose early departure has left a great void in our midst. Contents page 1. Introduction 314 2. The theoretical machinery 317 2.1. Zeeman depolarization319 2.2. Ultralow energy collisions319 3. Rotational quenching 321 3.1. Neutral systems with closed-shell molecules322 3.2. Neutral syst...

Ab initio post-Hartree-Fock calculations are performed for the potential energy curve of the LiHe+ diatomic system and for the optimal structures of Li(He)(n)(+) clusters, with n from 1 to 6. MP4 optimizations with the cc-pVQZ basis set have been carried out and the results compared with the structures obtained by energy optimization procedure using pairwise potentials. The results are shown to remain very close to those obtained by including many-body effects in the full geometry optimization. (c) 2005 Elsevier B.V. All rights reserved.

The ab initio calculation of the interaction forces between the LiH+ molecular ion, at its equilibrium geometry, and several He atoms is carried out in order to isolate and assess the importance of many-body contributions in the search for realistic energy and geometry data. The full potential energy surface (PES) with a single helium partner is obtained first by using an aug-cc-pVQZ basis set for He and higher quality ones for Li and H. The calculations were performed at the CAS-SCF plus MRCI level for the lowest potential energy surface over a total of 480 grid points of the two intermolecular Jacobi coordinates, whereas the excited state surface has also been examined in order to exclude the presence of any significant nonadiabatic interaction between the two PESs. A numerical fit of the lower surface is presented and the general physical changes of the ionic interaction when going from the lower to the upper of the two potentials are described and discussed. The fairly limited importance of many-body effects for such systems is seen from further ab initio calculations including several He atoms: our results suggest that, at least in the present case, no strong charge migration occurs after He attachment, and therefore, one could realistically model larger clusters by implementing a sum-of-potentials approach via the presently computed PES.

The quantum treatment of the collisional excitation of rotations in H 2 and N 2 gases as test molecules is carried out within a space-fixed frame of reference by solving the multichannel close-coupled equations using an approach newly developed in our group, i.e. the modified variable phase approximation (MVPA). The interaction potentials contain the static, exchange and correlation-polarisation contributions and are obtained via a local, multipolar expansion formulation from ab initio data. The results are compared with existing experiments and produce numerically converged rotationally inelastic cross-sections obtained from an exact molecular-frame treatment of the problem.

The potential energy surface (PES) for the interaction between Li-2((1)Sigma(g)(+)) and He-4 has been computed using an accurate, post-Hartree-Fock quantum calculation for its ground electronic state. The orientational anisotropy of the forces and the interplay between repulsive and attractive effects within the PES are analyzed to extract information on the possible existence of bound states in the triatomic system. The structures of a few of the Li-2(He)(n) small clusters are examined by comparing a classical approach with a full quantum one to generate bound configurations and to extract information on the possible spatial arrangements of the smaller clusters via a vis the location of the Li-2 dopant. Some significant consequences on the Li-2 behavior in larger clusters and droplets are drawn from the above findings., University of Rome ‘‘La Sapienza’’ Scientific Committee; CASPUR Supercomputing Center; INFM Institute

Calculations for the reactive potential energy surfaces, which are relevant for examining the low-energy channels connected with the LiH 2 + three atom ionic system, are carried out using a multireference valence bond (MRVB) approach. More than 11.000 points have been computed over the grid of the three relevant coordinates (two bond distances and the enclosed angle) and the lowest three electronic states have been followed over the spatial configuration of the above coordinates. Several aspects of the reactive behavior could be gleaned from an analysis of the computed surfaces and various features of the reactive outcomes are extracted from that analysis.

The vibrational features and molecular structures of complexes formed by a series of uranyl-salophen receptors with simple anions, such as Cl(-) , H(-) , and HCOO(-) , have been investigated in the gas phase. Spectra of the anionic complexes were studied in the $\tilde \nu $=800-1800 cm(-1) range by mass-selective infrared multiple photon dissociation (IRMPD) spectroscopy with a continuously tunable free-electron laser. The gas-phase decarboxylation of the formate adducts produces uranyl-salophen monohydride anions, which have been characterized for the first time and reveal a strong UH bond, the nature of which has been elucidated theoretically. The spectra are in excellent agreement with the results obtained from high-quality ab initio calculations, which provided the structure and binding features of the anion-receptor complexes.

The present study addresses the problem of establishing from fully ab initio quantum methods some quantitative features of the chemical interactions which play an important role in the ionic lithium chemistry of astrophysical relevance. In particular, the LiH+2 energetics is examined by looking at the various possible chemical channels producing LiH, LiH+, H2 and H+2. An accurate evaluation of the relative energy landscapes as the complex breaks up into its asymptotic partners is presented for the first time. It allows us to clearly select those reactive pathways which can be excluded when setting up a kinetic modeling of the lithium chemistry network in early universe processes.

Recent calculations on the rigid rotor surface for the LiH–He interaction [B. K. Taylor and R. J. Hinde, J. Chem. Phys. 111, 973 (1999)] surmised that the well depth and anisotropy of the new surface differ substantially from the latest valence bond calculations for the same system [F. A. Gianturco, S. Kumar, S. K. Pathak, M. Raimondi, M. Sironi, J. Gerratt, and D. L. Cooper, Chem. Phys. 215, 227 (1997)]. We examine in detail the performance of both these potential energy surfaces once employed to generate quantum observables which can be compared with experiments. Our computations clearly show that the two surfaces exhibit small differences in their short-range repulsive anisotropy and larger differences in well depths. The latter however cannot be assessed as yet from existing experiments. The different behavior of their wells in supporting van der Waals bound states is also examined and spectroscopic experiments are suggested for detecting possible transitions between such states.

The ab initio potential energy surface (PES) already computed for the title system is employed here to study the behaviour of the collisional energy transfer processes over a broad range of energies. The quantum evaluation of rotationally and vibrationally inelastic partial integral cross sections is carried out under different angular momentum coupling conditions and the results are closely analysed in terms of the specific features of the coupling PES. State-to-state rate constants for excitation and relaxation processes are obtained in a broad range of temperatures and the overall efficiency of the collisional energy transfer is analysed. The cooperative effect between the rotational anisotropy and the vibrational excitations is clearly shown and discussed.

The first experimental study of the X-ray absorption spectrum (XAS) of the allyl free radical, CH(2)CHCH(2), is reported. A supersonic He seeded beam of hyperthermal allyl radicals was crossed by a high resolution synchrotron radiation (SR) in the focus of a 3D ion momentum imaging time-of-flight (TOF) spectrometer to investigate the soft X-ray absorption and fragmentation processes. The XAS, recorded as Total-Ion-Yield (TIY), is dominated by C1s electron excitations from either the central carbon atom, C(C), or the two terminal carbon atoms, C(T), to the frontier orbitals, the semi-occupied-molecular-orbital (SOMO) and the lowest-unoccupied-molecular-orbital (LUMO). All of the intense features in the XAS could only be assigned with the aid of ab initio spectral simulation at the Multi-Configuration Self-Consistent-Field (MCSCF) level of theory, this level being required because of the multi-reference nature of the core-excited state wavefunctions of the open shell molecule. The ionization energies (IEs) of the singlet and triplet states of the C1s ionized allyl radical (XPS) were also calculated at the MCSCF level.

Variational and diffusion Monte Carlo (VMC and DMC) calculations are presented for anionic electrolytes solvated in (4)He. The electrolytes have the general structure X(-)(He)(N), with X=F, Cl, Br and I, and N varying up to 40 (41 for I(-)). The overall interaction potential is obtained from accurate ab initio data for the two-body components and then using the sum-of-potentials approximation. Our computational scheme is a robust procedure, giving us accurate trial wavefunctions that can be used to perform high-quality DMC calculations. The results indicate very marked delocalization and permanence of the liquid-like quantum features of the solvent adatoms surrounding the anionic impurities. This finding stands in contrast to the more structured, solid-like behavior of the quantum solutions with alkali metal cations embedded in He nanodroplets. While other negatively charged species such as H(-) have shown an overall repulsive interaction with He, the present calculations clearly indicate that the halogen anions remain solvated within liquid-like solvent "bubbles" of species-dependent size.

An accurate ab initio potential energy surface has been employed for the treatment of the full quantum dynamics for isotopic exchange reaction $^{4}\mathrm{He}^{3}\mathrm{He}_{2}^{+}+^{4}\mathrm{He}$. State-to-state reactive probabilities have been obtained using a time-independent approach at ultralow collision energies. More than one total angular momentum has been calculated in order to provide a converged rate constant for the title reaction within the ultralow temperature regime. The reaction is found to become faster than the Langevin value when $T\ensuremath{\rightarrow}0$, thus providing connection with experiments with sympathetically cooled molecular ions or superfluid helium nanodroplets.

The collisional relaxation of rotationally ``hot'' OH molecules in He as a buffer gas has been studied as a fully quantum event using an ab initio potential energy surface and the exact dynamical coupling of the relevant angular momenta during the process. The range of energies considered corresponds to the ultralow temperatures of cold traps and the calculations were carried out down to the Wigner regime of cross section behavior. It is shown that the general dependence of the inelastic processes on rotational angular momentum and parity clearly indicates a fairly marked size dependence of the final cross sections on the specific fine structure levels in which the target radical is being prepared to undergo relaxation.

The potential energy surfaces (PES) for the interaction between Li2 (1∑+g) and 4He has been computed earlier by using an accurate, post-Hartree-Fock quantum calculation for its ground electronic state and was presented in previous papers1,2. Here we report a revised version of the same interaction that we have generated using instead an empirical approach that replaces the two-body contributions in the ab-initio potential with external estimates. We have repeated Diffusion Monte Carlo calculations to obtain the quantum ground states for the Li2Hen clusters already discussed in our previous paper1 and we compare the two sets of fundings.

Three-dimensional potential energy surfaces (PESs) have been computed, and numerically fitted, for the two lowest electronic states of the LiH2+ system, which are of importance for the astrophysically relevant LiH++H→Li++H2 and LiH+H+→Li+H2+ exoergic reactions. We extend the recently computed 11 000 multi reference valence bond ab initio energy values [Martinazzo et al., Chem. Phys. 287, 335 (2003)] with 600 multireference configuration interaction calculations with complete active self-consistent field reference functions and a large Li(12s10p4d1f)/H(8s6p3d1f) basis set. We have fitted the full set of energy values with a modified Aguado–Paniagua ansatz that correctly takes into account in this ionic system the important long-range contributions to the potential. Calibration calculations on the three-body potential term and the use of essentially exact results for the two-body contributions allow us to estimate the overall accuracy of the analytic PESs to be within that required for accurate quantum scattering calculations. The above reactions can be treated adiabatically because of the large energy gap separating the two electronic states. The relevant potential energy surfaces have a very different shape. On the one hand, the ground-state PES shows a simple structure, with a downhill route to the products and a shallow well at the C2v geometry which lies 0.286 eV below the Li++H2 asymptote. On the other hand, the first excited state is characterized by one deep, dipole-charge well which lies 1.315 eV below the LiH+H+ asymptote, one charge-induced dipole well 0.586 eV below the Li+H2+ asymptote, and a saddle point between them which lies 0.227 eV below the LiH+H+ asymptote. A conical intersection with the second excited state has been found but not yet studied in detail, since we deemed it to be of no direct relevance for the above reactions.

We report an ab initio study of the dynamics of the reaction F + D2→DF + D, where D2 is initially in a rotationally excited state (j = 2). The possibility of obtaining ultra-cold molecules and of investigating reaction dynamics at ultra-low temperature relies on the production of molecules in a well defined quantum state and it is important to know the relative efficiency of the rotational quenching and of the chemical reaction. We examine here a reaction with an activation barrier, the reaction of F with D2, and we find that quenching dominates the reaction when the initial rotational level lies energetically below the barrier, so severe trap loss may occur before the reaction can take place.

The full Born-Oppenheimer (BO) potential energy surface that describes the interaction between a vibrating and rotating LiH molecule and an He atom, obtained from ab initio VB calculations described before (Chem. Phys. 1997, 215, 287), is employed here to evaluate the corresponding partial integral cross sections over a range of energies of astrophysical relevance. The process examined involves rotovibrational heating of the initially “cold” target molecule in a single-collision situation, and it provides specific indications on the process efficiency for modeling global kinetics of primordial clouds. The details of the dynamical coupling produced and some specific features of the potential energy surface are analyzed in relation to the behavior of the inelastic cross sections. The average energy transfer values and the relaxation rates are obtained from quantum dynamics and found to be unexpectedly large for such a weakly interacting system.

Diffusion Monte Carlo calculations are carried out for clusters of OH- (1Sigma+) with N 4He atoms, N varying up to 15, while classical configurations from a genetic algorithm optimization are obtained up to N=20. The overall interaction potential is assembled from ab initio data for the partners using the sum-of-potentials scheme. In contrast with the cationic dopants' behavior, the results indicate a very marked spatial delocalization and quantum features of the solvent adatoms surrounding the anionic impurity, thus making classical calculations of solvent's spatial locations of only limited use. In spite of the generally known repulsive interaction of negative charges in He droplets, the calculations show that this polar molecular anion is solvated by a liquidlike solvent layer, reminiscent of what happens in pure helium droplets.

Calculations have been carried out for the vibrational quenching of excited H(2) molecules which collide with Li(+) ions at ultralow energies. The dynamics has been treated exactly using the well-known quantum coupled-channel expansions over different initial vibrational levels. The overall interaction potential has been obtained from the calculations carried out earlier by our group using highly correlated ab initio methods. The results indicate that specific features of the scattering observables, e.g., the appearance of Ramsauer-Townsend minima in elastic channel cross sections and the marked increase of the cooling rates from specific initial states, can be linked to potential properties at vanishing energies (sign and size of scattering lengths) and to the presence of either virtual states or bound states. The suggestion is made such that by selecting the initial state preparation of the molecular partners, the ionic interactions would be amenable to controlling quenching efficiency at ultralow energies.