Coordination polymers (CPs), including metal-organic frameworks (MOFs), are crystalline materials with promising applications in electronics, magnetism, catalysis, and gas storage/separation. However, the mechanisms and pathways underlying their formation remain largely undisclosed. Herein, we demonstrate that diffusion-controlled mixing of reagents at the very early stages of the crystallization process (i.e., within ?40 ms), achieved by using continuous-flow microfluidic devices, can be used to enable novel crystallization pathways of a prototypical spin-crossover MOF towards its thermodynamic product. In particular, two distinct and unprecedented nucleation-growth pathways were experimentally observed when crystallization was triggered under microfluidic mixing. Full-atom molecular dynamics simulations also confirm the occurrence of these two distinct pathways during crystal growth. In sharp contrast, a crystallization by particle attachment was observed under bulk (turbulent) mixing. These unprecedented results provide a sound basis for understanding the growth of CPs and open up new avenues for the engineering of porous materials by using out-of-equilibrium conditions.

We present accurate ab initio calculations on the structural properties of a gas-phase reaction of possible interest for Saturn's outer atmosphere chemistry, in which the CH2 molecule has been detected. In the present study, that molecule is made to react with the H- anion to form the CH- species, one considered as a possible intermediate in ionic processes networks. The results indicate that this reaction is markedly exothermic and proceeds with the formation of an intermediate, which occurs via only a shallow barrier below the reagents and progresses directly to the product region. The corresponding rate coefficients of reactions are also computed by making use of the variational transition state theory modeling and found to efficiently lead to the formation of the final anion even at the lower temperatures of interstellar medium conditions.

Structural features and enthalpy details are presented for the title reactions, both for the exothermic (forward) path to NH formation and for the endothermic (reverse) reaction to NH formation. Both pathways have relevance for the nitrogen chemistry in the interstellar medium (ISM). They are also helpful to document the possible role of H in molecular clouds at temperatures well below room temperature. The structural calculations are carried out using different ab initio methods and are further employed to obtain the reaction rates down to the interstellar temperatures detected in earlier experiments. The reaction rates are obtained from the computed minimum energy path (MEP) using the variational transition-state theory (VTST) approach. The results indicate very good accord with experiment results at room temperature, while measured low temperature data down to 8 K are well described using an appropriately modified VTST approach. This is done by employing a temperature-dependent scaling, from room temperature conditions down to the lower ISM temperatures, which acknowledges the noncanonical behavior of the fast, barrierless exothermic reaction. The reasons for this behavior and the need for improving on the VTST method when used away from room temperatures are discussed.

Gas phase ion chemistry has fundamental and applicative purposes since it allows the study of the chemical processes in a solvent free environment and represents models for reactions occurring in the space at low and high temperatures. In this work the ion-molecule reaction of sulfur dioxide ion So(2)(+) with carbon monoxide CO is investigated in a joint experimental and theoretical study. The reaction is a fast and exothermic chemical oxidation of CO into more stable CO2 by a metal free species, as SO2+, excited into ro-vibrational levels of the electronic ground state by synchrotron radiation. The results show that the reaction is hampered by the enhancement of internal energy of sulfur dioxide ion and the only ionic product is SO (+). The theoretical approach of variational transition state theory (VTST) based on density functional electronic structure calculations, shows an interesting and peculiar reaction dynamics of the interacting system along the reaction path. Two energy minima corresponding to [S0(2)-00] (+) and [OS-OCO] (+) complexes are identified. These minima are separated by an intersystem crossing barrier which couples the bent B-3(2) state of CO2 with C-2(v) symmetry and the (1)A(1) state with linear D-infinity h symmetry. The spin and charge reorganization along the minimum energy path (MEP) are analyzed and eventually the charge and spin remain allocated to the SO (+) moiety and the stable CO2 molecule is easily produced. There is no bottleneck that slows down the reaction and the values of the rate coefficient k at different temperatures are calculated with capture theory. A value of 2.95 x 10 (-10) cm(3)s (-1)molecule (-1) is obtained at 300 K in agreement with the literature experimental measurement of 3.00 x 10( -10) +/- 20% cm(3)s( -l)molecule (-1), and a negative trend with temperature is predicted consistently with the experimental observations.

The study of transitionmetal coordination complexes has played a key role in establishing quantum chemistry concepts such as that of ligand field theory. Furthermore, the study of the dynamics of their excited states is of primary importance in determining the de-excitation path of electrons to tailor the electronic properties required for important technological applications. This work focuses on femtosecond transient absorption spectroscopy of Cobalt tris(acetylacetonate) (Co(AcAc)(3)) in solution. The fast transient absorption spectroscopy has been employed to study the excited state dynamics after optical excitation. Density functional theory coupled with the polarizable continuum model has been used to characterize the geometries and the electronic states of the solvated ion. The excited states have been calculated using the time dependent density functional theory formalism. The time resolved dynamics of the ligand to metal charge transfer excitation revealed a biphasic behavior with an ultrafast rise time of 0.07 +/- 0.04 ps and a decay time of 1.5 +/- 0.3 ps, while the ligand field excitations dynamics is characterized by a rise time of 0.07 +/- 0.04 ps and a decay time of 1.8 +/- 0.3 ps. Time dependent density functional theory calculations of the spin-orbit coupling suggest that the ultrafast rise time can be related to the intersystem crossing from the originally photoexcited state. The picosecond decay is faster than that of similar cobalt coordination complexes and is mainly assigned to internal conversion within the triplet state manifold. The lack of detectable long living states (>5 ps) suggests that non-radiative decay plays an important role in the dynamics of these molecules.

The ultrafast dynamics of zwitterionic and cationic Rhodamine B in ethanol have been investigated using TDDFT calculations and ultrafast transient absorption spectroscopy. The calculations show that the zwitterionic form exhibits an electronically excited dark state which could potentially quench the initially photoexcited state, while in the case of cationic form the lowest excited lying dark state is outside the energy region of interest and cannot explain its quenching. Due to similarities in the relaxation dynamics of the two molecules, it is suggested that the electronically excited dark state may not play such an important role in the quenching process of this dye as previously proposed. Experimental evidence presented suggests that a quenching mechanism is active on the picosecond timescale for both forms of Rhodamine B.

The adsorption of Si atoms on a metal surface might proceeds through complex surface processes whose rate is differently determined by factors as temperature, Si coverage and metal cohesive energy. Among other transition metals, iridium is a special case since the Ir (111) surface was reported first, in addition to Ag(111), as suitable for the epitaxy of silicene monolayers. In this study we followed the adsorption of Si on the Ir(111) surface by high resolution core level photoelectron spectroscopy starting from the clean metal surface up to a coverage exceeding one monolayer in the temperature range between 300 and 670 K. Density functional theory calculations were carried out to evaluate the stability of the different Si adsorption configurations as a function of the coverage. Results indicate that at low coverage the Si adatoms tend to occupy the hollow Irsites, but a small fraction of them penetrates in the first Ir layer. Si penetration in the Ir surface can take place if the energy gained upon Si adsorption is used to displace the Ir surface atoms rather then being differently dissipated. At Si coverage 1 monolayer the Ir4f spectrum signals that not only the metal surface but also the layers underneath are perturbed. Our results point out that the Si/Ir(111) interface is unstable towards Si-Ir intermixing, in agreement with the silicide phase formation reported in the literature for the reverted interface

The reaction dynamics and the temperature-dependent kinetic trend of the SO2 center dot+ ion-molecule reactions with water and methane have been studied using the tunable synchrotron radiation to produce excited SO2 center dot+ ions and ab-initio methods. The experimental results show that only one product, HSO2+, is formed in both reactions and its yield displays different trends with the photon energy. DFT and VTST calculations have been used to explore the dynamics of the reactions and to calculate the rate constants at different temperatures.

We investigate the relative efficiencies of low-temperature chemical reactions in the interstellar medium with H- anion reacting in the gas phase with cyanopolyyne neutral molecules, leading to the formation of anionic CxN- linear chains of different lengths and of H-2. All the reactions turn out to be without barriers, highly exothermic reactions that provide a chemical route to the formation of anionic chains of the same length. Some of the anions have been observed in the dark molecular clouds and in the diffuse interstellar envelopes. Quantum calculations are carried out for the corresponding reactive potential energy surfaces for all the odd-numbered members of the series (x = 1, 3, 5, 7). We employ the minimum energy paths to obtain the relevant transition state configurations and use the latter within the variational transition state model to obtain the chemical rates. The present results indicate that at typical temperatures around 100 K, a set of significantly larger rate values exists for x = 3 and x = 5, while the rate values are smaller for CN- and C7N-. At those temperatures, however, all the rates turn out to be larger than the estimates in the current literature for the radiative electron attachment (REA) rates, thus indicating the greater importance of the present chemical path with respect to REA processes at those temperatures. The physical reasons for our findings are discussed in detail and linked with the existing observational findings.

In this work an experimental and theoretical study on the formation of HSO2 + ion from the SO2 ?++CH4 and SO2 ?++H2O ion-molecule reactions at different temperatures is reported. Tunable synchrotron radiation was used to produce the SO2 ?+ ion in excited ro-vibrational levels of the ionic ground state X2A1 and mass spectrometry was employed to identify the product ions. Calculations in the frame of the density functional theory and variational transition state theory were combined to explore the dynamics of the reactions. The experimental results show that HSO2 + is the only product in both reactions. Its yield decreases monotonically with photon energy in the SO2 ?++H2O reaction, while it decreases at first and then increases in the SO2 ?++CH4 reaction. Theory confirms this trend by calculating the rate constants at different temperatures and explains the results by means of the polar, spin and charge effects as well as structural reorganization occurring in the reaction coordinate. The dynamic behavior observed in these two reactions is of general and fundamental interest. It can also provide some insights on the role of these reactions in astrochemistry as well as in their use as models for bond-activation reactions.

The surface electronic structure of Si(1 1 1)-$7\times 7$ has been studied by angle-resolved photo electron spectroscopy. Replicas of the S 1 surface state are found in correspondence with several $7\times 7$ unit cells in the reciprocal space. This observation resolves in a direct way the long-standing dichotomy between the structural and electronic properties of the system previously discussed on the basis of the $2\times 2$ or $\sqrt{3}\times \sqrt{3}$ R30° surface models.

Context. The HF molecule has been proposed as a sensitive tracer of diffuse interstellar gas, while at higher densities its abundance could be influenced heavily by freeze-out onto dust grains.

Using quantum chemical methods, we investigate the possible outcomes of H- reactions with acetylene and diacetylene molecules. We find both reactions to be exothermic reactions without barriers, yielding stable anions of the corresponding polyynes: C2H- and C4H-. We show in this work that the computed chemical rates in the case of the formation of the C4H- anion would be larger than those existing for the direct radiative electron attachment (REA) process, the main mechanism generally suggested for their formation. In the case of the C2H- anion, however, the present chemical rates of formation at low T are even lower than those known for its REA process, both mechanisms being inefficient for its formation under astrochemical conditions. The present results are discussed in view of their consequences on the issue of the possible presence of such anions in the ISM environments. They clearly indicate the present chemical route to C2H- formation to be inefficient at the expected temperatures of a dark molecular cloud, whereas this is found not to be the case for the C4H-, in line with the available experimental findings.

The supramolecular chemistry at surfaces has been extensively studied by quantum and classical computational models in order to simulate and reproduce the correct energetics and structures of adsorbed molecules on surfaces at various coverages. We have developed a classical tool able to sample the configuration space overcoming the topological constraints of the standard classical molecular dynamics. Our model is based on the charge equilibration procedure combined with an anisotropic pairwise atomic interaction where an angular dependence, with respect to the metal surface, is explicitly taken into account. The D-alaninol molecule has been chosen as a prototype of a flexible and multifunctional chemical compound which can form manifold complex configurations upon absorption on a metal surface. A detailed analysis of molecular structures and energetics of partial and full coverage has been carried out. The experimental STM image of the monolayer is correctly reproduced by our calculations, indicating that this new approach represents a step forward in the efficient simulation of complex molecular self-assembly.

The conformational landscape of (S)-1-(4-chlorophenyl)ethanol, its monohydrated complex, and its diastereomeric adducts with R- and S-butan-2-ol, have been investigated by resonant two-photon ionization (R2PI) spectroscopy coupled with time-of-flight mass spectrometry. Theoretical calculations at the D-B3LYP/6-31++G** level of theory have been performed to assist in the interpretation of the spectra and in the assignment of the structures. The R2PI spectra and the predicted structures have been compared with those obtained on the analogous non-halogenated and fluorinated systems, i.e., (R)-1-phenylethanol and (S)-1-(4-fluorophenyl)ethanol, respectively. It appears that the presence of chlorine atom in the para position of the aromatic ring does not influence the overall geometry of bare molecule and its complexes with respect to the non-halogenated analogous systems. Anyway, it affects the electron density in the pi system, and in turn the strength of OH···pi and CH···pi interactions. A spectral chiral discrimination is evident from the R2PI spectra of the diastereomeric adducts of (S)-1-(4-chlorophenyl)ethanol with the two enantiomers of butan-2-ol.

We discuss application of the Auger parameter and Wagner plot concepts to the study of small copper clusters deposited on various supports such as C(graphite), SiO2 and Al2O3. We demonstrate that the cluster size and the electronic properties of the support influence the shifts of both the binding energy of the Cu 2p3/2 transition and the kinetic energy of the Cu L3M45M45; 1G Auger transition. We find that the Cu L3M45M45; 1G-2p3/2 Auger parameter and Wagner plot allow one to single out and measure both initial- and final-state effects with a detail which is superior to that achieved in photoemission studies.

The barrierless, exothermic reactions of H- with HCnN cyanopolyynes, with n = 1 and 3, are analyzed using ab initio calculations of the interaction forces. The shape of the reactive potential energy surface suggests the most efficient approach of H- to be on a nearly collinear arrangement on the H-side of HCnN. Using simple transition state formulation of the reaction rates, which are obtained via calculation of the partition functions of each transition state configuration, provides a new non-Langevin behavior of the reaction which can help explain the unexpectedly large density of CN- formation found in observations. A similar procedure is also employed for the reaction of H- with HC3N and the differences in the results, indicating a lower efficiency of the latter reactivity compared with that for CN-, are discussed in this paper.

Electron and positron scattering processes in the gas-phase are analysed for uracil and pyrimidine molecules using a multichannel quantum approach at energies close to threshold. The special effects on the scattering dynamics induced by the large dipole moments in both molecules on the spatial features of the continuum leptonic wavefunctions are here linked to the possible bound states of the Rydberg-like molecular anions or 'positroned' molecules which could be reached via further couplings with molecular internal degrees of freedom.

The chemical physics of halomethanes is an important and challenging topic in several areas of chemistry in particular in the chemistry of the atmosphere. Among the class of halomethanes, the diiodomethane molecule has attracted some interest in the last years, but despite this, the information on its radical cation [CH2I2](+) is still limited. In this work, we measured and calculated the appearance energy (AE) of the ionic fragments I2 (+) and CH2 (+) and correlated the different fragmentation channels to the electronic states of the cation via photoelectron-photoion coincidence (PEPICO) experiments. In the case of the CH2/I2 (+) channel, the experimentally determined AE is in excellent agreement with the adiabatic theoretical value while a discrepancy is observed for the CH2 (+)/I2 channel. This discrepancy can be understood accounting for a fragmentation involving the formation of two I atoms (CH2 (+)/2I channel), which, as explained by time dependent density functional theory (TD-DFT) calculations, occurs when [CH2I2](+) excited states are involved.

The modelization of the Si/Ag(110) and Si/Ag(111) systems is generally based on the assumption of a complete immiscibility between silicon and silver. Recent results, on the contrary, demonstrated that in both cases the silver substrate is altered upon silicon deposition through Si-Ag exchange processes, either inducing substrate reconstructions [1] and faceting [2], or suggesting that Si-Ag reactivity must be taken into account. In this talk, I will at first survey our recent results on the Si/Ag(110) system [5], showing novel structural models for nanoribbons obtained considering missing-row reconstructions of the Ag(110) substrate. On the basis of STM measurements, Si coverage evaluation and density functional theory simulations, our models result to be thermodynamically stable, consistent with the experimental Si and Ag coverages, and yield simulated STM images in agreement with the measured data; in contrast, silicene-based models yield unsatisfactory results. Next, I'll discuss about our recently published paper [6] on the Si/Ag(111) that describes, through a combined DFT and STM study, the basic exchange mechanism between Si and the topmost layer Ag atoms that results in the growth of the well-known different kind of reconstructed domains inside, rather than on top, the first Ag(111) layer. [1] R. Bernard, T. Leoni, A. Wilson, T. Lelaidier, H. Sahaf, E. Moyen, L. Assaud, L. Santinacci, F. Leroy, F. Cheynis, A. Ranguis, H. Jamgotchian, C. Becker, Y. Borensztein, M. Hanbücken, G. Prévot, and L. Masson, Phys. Rev. B 88, 121411 (2013). [2] F. Ronci, G. Serrano, P. Gori, A. Cricenti, and S. Colonna, Phys. Rev. B 89, 115437 (2014). [3] J. Sone, T. Yamagami, Y. Aoki, K. Nakatsuji, and H. Hirayama, New J. Phys. 16, 095004 (2014). [4] G. Prévot, R. Bernard, H. Cruguel, and Y. Borensztein, Appl. Phys. Lett. 105, 213106 (2014). [5] C. Hogan, S. Colonna, R. Flammini, A. Cricenti, and F. Ronci, submitted. [6] M Satta, S. Colonna, R. Flammini, A. Cricenti, and F. Ronci, Phys. Rev. Lett. 115, 026102 (2015).