Unveiling the Reaction Mechanism of the N(D) + Pyridine Reaction: Ring-Contraction versus 7-Membered-Ring Formation Channels.

Despite the relevance of the reactions of the prototypical nitrogen-containing six-membered aromatic molecule (N-heterocyclic) of pyridine (CHN) in environmental science, astrochemistry, planetary science, prebiotic chemistry, and materials science, few experimental/theoretical studies exist on the bimolecular reactions involving pyridine and neutral atomic/molecular radicals. We report a combined experimental and theoretical study on the elementary reaction of pyridine with excited nitrogen atoms, N(D), aimed at providing information about the primary reaction products and their branching fractions (BFs). From previous crossed molecular beam (CMB) experiments with mass-spectrometric detection and present synergistic calculations of the reactive potential energy surface (PES) and product BFs we have unveiled the reaction mechanism.

Pentaphosphorylation via the Anhydride of Dihydrogen Pentametaphosphate: Access to Nucleoside Hexa- and Heptaphosphates and Study of Their Interaction with Ribonuclease A.

Pentametaphosphate is the little studied cyclic pentamer of the metaphosphate ion, [PO] . We show that the doubly protonated form of this pentamer can be selectively dehydrated to provide the anhydride [PO] (). This trianion is the well-defined condensed phosphate component of a novel reagent for attachment of a pentaphosphate chain to biomolecules all in one go.

Revisiting Numerical Solutions of Weakly Bound Noble Gases' Vibrational Energy Levels Modeled by the Improved Lennard-Jones Potential.

We revisit the numerical solutions of vibrational eigenstates of weakly bound homonuclear and heteronuclear noble gas pairs by applying a Fortran program based on the Numerov method. The harmonic, Lennard-Jones (LJ), Morse, Tang-Toennies (TT), and Improved Lennard-Jones (ILJ) potential models have been implemented to represent the potential energy curves (PECs). The obtained vibrational energies spectrum was tested on the experimental data and accurate ab initio calculations at CCSD(T)/CBS level.

OH(Π) + CH Reaction: A Combined Crossed Molecular Beam and Theoretical Study.

The reaction between the ground-state hydroxyl radical, OH(Π), and ethylene, CH, has been investigated under single-collision conditions by the crossed molecular beam scattering technique with mass-spectrometric detection and time-of-flight analysis at the collision energy of 50.4 kJ/mol. Electronic structure calculations of the underlying potential energy surface (PES) and statistical Rice-Ramsperger-Kassel-Marcus (RRKM) calculations of product branching fractions on the derived PES for the addition pathway have been performed.

Development of accurate potentials for the physisorption of water on graphene.

From coupled-cluster singles and doubles model including connected triples corrections [CCSD(T)] calculations on the water dimer and B97D/CC on the water-circumcoronene complex at a large number of randomly generated conformations, interaction potentials for the physisorption of water on graphene are built, accomplishing almost sub-chemical accuracy. The force fields were constructed by decomposing the interaction into electrostatic and van der Waals contributions, the latter represented through improved Lennard-Jones potentials. Besides, a Chemistry at Harvard Macromolecular Mechanics (CHARMM)-like term was included in the water-water potential to improve the description of hydrogen bonds, and an induction term was added to model the polarization effects in the interaction between water and polyaromatic hydrocarbons (PAHs) or graphene.

Reactions O(P, D) + HCCCN(XΣ) (Cyanoacetylene): Crossed-Beam and Theoretical Studies and Implications for the Chemistry of Extraterrestrial Environments.

Cyanoacetylene HCCCN), the first member of the cyanopolyyne family (HCN, where = 3, 5, 7, ...

Multilayer Graphtriyne Membranes for Separation and Storage of CO: Molecular Dynamics Simulations of Post-Combustion Model Mixtures.

The ability to remove carbon dioxide from gaseous mixtures is a necessary step toward the reduction of greenhouse gas emissions. As a contribution to this field of research, we performed a molecular dynamics study assessing the separation and adsorption properties of multi-layered graphtriyne membranes on gaseous mixtures of CO, N, and HO. These mixtures closely resemble post-combustion gaseous products and are, therefore, suitable prototypes with which to model possible technological applications in the field of CO removal methodologies.

Fragmentation of interstellar methanol by collisions with He˙: an experimental and computational study.

Methanol is a key species in astrochemistry as its presence and reactivity provides a primary route to the synthesis of more complex interstellar organic molecules (iCOMs) that may eventually be incorporated in newly formed planetary systems. In the interstellar medium, methanol is formed by hydrogenation of CO ices on grains, and its fate upon collisions with interstellar ions should be accounted for to correctly model iCOM abundances in objects at various stages of stellar evolution. The absolute cross sections (CSs) and branching ratios (BRs) for the collisions of He˙ ions with CHOH are measured, as a function of the collision energy, using a Guided Ion Beam Mass Spectrometer (GIB-MS).

Semiempirical Potential in Kinetics Calculations on the HCN + CN Reaction.

The reaction between the cyano radical CN and cyanoacetylene molecule HC3N is of great interest in different astronomical fields, from star-forming regions to planetary atmospheres. In this work, we present a new synergistic theoretical approach for the derivation of the rate coefficient for gas phase neutral-neutral reactions. Statistic RRKM calculations on the Potential Energy Surface are coupled with a semiempirical analysis of the initial bimolecular interaction.

Toward a Generalized Hückel Rule: The Electronic Structure of Carbon Nanocones.

In this work, we investigate a particular class of carbon nanocones, which we name graphannulenes, and present a generalized Hückel rule (GHR) that predicts the character of their ground state based on simply the three topological indices that uniquely define them. Importantly, this rule applies to both flat and curved systems, encompassing a wide variety of known structures that do not satisfy the "classic" 4 + 2 rule such as coronene, corannulene, and Kekulene. We test this rule at the Hückel level of theory for a large number of systems, including structures that are convex and flat, with a saddle-like geometry, and at the CASSCF level of theory for a selected representative subset.

Grand Canonical Monte Carlo Simulations to Determine the Optimal Interlayer Distance of a Graphene Slit-Shaped Pore for Adsorption of Methane, Hydrogen and their Equimolar Mixture.

The adsorption-for separation, storage and transportation-of methane, hydrogen and their mixture is important for a sustainable energy consumption in present-day society. Graphene derivatives have proven to be very promising for such an application, yet for a good design a better understanding of the optimal pore size is needed. In this work, grand canonical Monte Carlo simulations, employing Improved Lennard-Jones potentials, are performed to determine the ideal interlayer distance for a slit-shaped graphene pore in a large pressure range.

Two-dimensional diamine-linked covalent organic frameworks for CO/N capture and separation: theoretical modeling and simulations.

Two-dimensional covalent organic frameworks (2D-COFs) with diamine-based linkers have been designed and investigated for CO2/N2 gaseous mixture adsorption and separation via a systematic theoretical study by combining density functional theory (DFT) calculations and force field-based molecular dynamics (MD) simulations. We explored the adsorption sites and adsorption energies of CO2/N2 on 2D-COFs. The gas uptake capacity, adsorption isotherms, permeability, and selectivity were simulated based on an improved formulation of force fields for mixture separation in post-combustion conditions.

Molecular Dynamics of CH/N Mixtures on a Flexible Graphene Layer: Adsorption and Selectivity Case Study.

We theoretically investigate graphene layers, proposing them as membranes of subnanometer size suitable for CH/N separation and gas uptake. The observed potential energy surfaces, representing the intermolecular interactions within the CH/N gaseous mixtures and between these and the graphene layers, have been formulated by adopting the so-called Improved Lennard-Jones (ILJ) potential, which is far more accurate than the traditional Lennard-Jones potential. Previously derived ILJ force fields are used to perform extensive molecular dynamics simulations on graphene's ability to separate and adsorb the CH/N mixture.

An Experimental and Theoretical Investigation of 1-Butanol Pyrolysis.

Bioalcohols are a promising family of biofuels. Among them, 1-butanol has a strong potential as a substitute for petrol. In this manuscript, we report on a theoretical and experimental characterization of 1-butanol thermal decomposition, a very important process in the 1-butanol combustion at high temperatures.

Tuning the magnetic properties of beryllium chains.

In this work we explore the effect of confining beryllium chains inside carbon nanotubes. Linear Ben systems are characterized by two states originating from the presence of edge orbitals localized at the chain extremities. The two spins occupying these orbitals are, in the gas phase, antiferromagnetically coupled, with the magnetic coupling J decaying exponentially as a function of increasing length of the chain.

Modeling the Interaction of Carbon Monoxide with Flexible Graphene: From Coupled Cluster Calculations to Molecular-Dynamics Simulations.

The interaction of CO with graphene was studied at different theoretical levels. Quantum-mechanical calculations on finite graphene models with the use of coronene for coupled cluster calculations and circumcoronene for B97D calculations showed that there was no preferential site for adsorption and that the most important factor was the orientation of CO relative to graphene. The parallel orientation was preferred, with binding energies around 9 kJ mol at the CCSD(T) and B97D levels, which was in good agreement with experimental findings.

N⁻₃ azide anion confined inside finite-size carbon nanotubes.

In this work, the confinement of an N[Formula: see text] azide anion inside finite-size single-wall zigzag and armchair carbon nanotubes of different diameters has been studied by wave function and density functional theory. Unrelaxed and relaxed interaction energies have been computed, resulting in a favorable interaction between the guest and host system. In particular, the largest interaction has been observed for the confinement in an armchair (5,5) carbon nanotube, for which a natural population analysis as well as an investigation based on the molecular electrostatic potential has been carried out.

Increasing Radical Character of Large [n]cyclacenes Unveiled by Wave Function Theory.

We have investigated the radicality and the vertical singlet-triplet energy gap of [n]cyclacenes (cyclic polyacenes) as a function of the system size for n even, from 6 to 22. The calculations are performed using the complete active space self-consistent field method and second-order n-electron valence perturbation theory. We present a systematic way for the selection of the active space in order to have a balanced description of the wave function as the size of the system increases.

An innovative synergistic grid approach to the computational study of protein aggregation mechanisms.

Thanks to the advances in grid technologies, we are able to propose here an evolution of our molecular simulator that, when moving to larger systems, instead of reducing the granularity of the dynamical treatment (as is often done in molecular dynamics studies of such systems) exploits the extra power of the grid approach to the end of preserving the detailed nature of theatomistic formulation of the interaction. Key steps of such evolution are: (1) the assemblage of the interaction based on a composition of the ab initio intramolecular data and a portable parameterization of the intermolecular potential linking ab initio evaluation of intramolecular potentials and the partitioning of molecular polarizability; (2) the exploitation of an efficient coordinated porting and running of molecular dynamics codes on the European grid distributed computing infrastructure. As a prototype case study, the N-methylacetamide dimer in vacuo has been considered and the formation of possible conformers is analyzed.

Modeling of energy transfer from vibrationally excited CO2 molecules: cross sections and probabilities for kinetic modeling of atmospheres, flows, and plasmas.

We present extended applications of an established theoretical and computational machinery suitable for the study of the dynamics of CO2+CO2 collisions, focusing on vibrational energy exchange, considered over a wide range of energies and rotational temperatures. Calculations are based on quasi-classical trajectories on a potential energy function (a critical component of dynamics simulations), tailored to accurately describe the intermolecular interactions, modeled by the recently proposed bond-bond semiempirical formulation that allows the colliding molecules to be stretchable, rather than frozen at their equilibrium geometry. In a previous work, the same potential energy surface has been used to show that modifications in the geometry (and in physical properties such as polarizability and charge distribution) of the colliding partners affect the intermolecular interaction and determine the features of the energy exchange, to a large extent driven by long-range forces.

A high-level ab initio study of the N2 + N2 reaction channel.

A new six-dimensional (6D) global potential energy surface (PES) is proposed for the full range description of the interaction of the N2(1Σg+)+N2(1Σg+) system governing collisional processes, including N atom exchange. The related potential energy values were determined using high-level ab initio methods. The calculations were performed at a coupled-cluster with single and double and perturbative triple excitations level of theory in order to have a first full range picture of the PES.

An extension of the grid empowered molecular simulator to quantum reactive scattering.

Within the activities of the D37 COST Action, we have further developed the quantum dynamics framework of the grid empowered molecular simulator (GEMS) implemented on the segment of the European grid available to the COMPCHEM (computational chemistry) virtual organization. GEMS does now include in a full ab initio approach, the evaluation of the detailed quantum (both time dependent and time independent) dynamics of small systems starting from the calculation of the electronic structure properties as well as the direct calculation of thermalized properties. Illustrative, full dimensional applications of the extended simulator to the H + H(2) , N + N(2) , and O + O(2) systems are presented.