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A detailed quantum chemical investigation of a new reaction mechanism possibly leading to the formation of cyanoketene (NC–CH═C═O) in the interstellar medium (ISM) was carried out. Different reaction channels have been found by the AutoMeKin program, and the structures and harmonic force fields of the key stationary points have been characterized at the density functional theory level employing last-generation double-hybrid functionals. Finally, single-point computations at those geometries by state-of-the-art composite wave function methods provided accurate energies for the evaluation of thermochemical and kinetic parameters in the framework of an Ab Initio Transition State Theory based Master Equation (AITSTME) strategy. Our results indicate that the barrier-less association reaction of the formyl radical (HCO•) to the cyanocarbene radical (HCCN) can lead to the formation of cyanoketene under the harsh conditions of the ISM. Canonical rate constants computed for temperatures up to 600 K show that the most abundant product is indeed cyanoketene. The formation of other, even more stable, species involves higher activation energies and/or less favorable multi-step processes. Furthermore, to aid the search of cyanoketene, still undetected in the ISM, its rotational spectrum was recorded up to 530 GHz. The refined set of spectroscopic constants obtained in this way allows for spectral predictions from the microwave to the terahertz region, particularly for the bright b-type transitions, which can be targeted for the identification of cyanoketene in spectral line surveys. Despite cyanoketene was already sought without success in a variety of astronomical sources, we suggest to look for it in those sources where HCO or HCCN have already been detected, namely, W3, NGC2024, W51, K3-50, IRC + 2016, and TMC-1.

The scaled roto-diffusion tensor that includes dissipative and energetic properties of a molecule introduced here describes molecular local and global flexibility allowing a rigorous hierarchical selection of the relevant dynamics.

Cyanoacetaldehyde (NC-CH2CH=O) is considered, together with guanidine and urea, as a precursor of the pyrimidine bases cytosine and uracil. Although it has not yet been detected in the interstellar medium (ISM), several hypotheses have been put forward about its synthesis in solution and in the gas phase. In this paper, we present a gas-phase model of the barrierless reaction between formyl (HCO) and cyanomethyl (CH2CN) radicals leading to cyanoacetaldehyde and focus on its evolution through isomerization and dissociation pathways. The potential-energy surface for all reactions has been explored by DFT calculations employing double-hybrid functionals and further refined through the "Cheap" composite scheme. Our results indicate that the direct association of the two reacting radicals (HCO and CH2CN) is strongly exothermic and thus thermodynamically favored under the harsh conditions of the ISM. Microcanonical rate constants computed with the help of the StarRate program for energies up to 6 kJ mol(-)(1) above the dissociation limit show that the most abundant products are the two conformers of cyanoacetaldehyde (nitrile and carbonyl groups in a cis or trans configuration) which, despite having comparable stability, are obtained with a cis/trans ratio of 0.35:0.65. The formation of other products with relative abundances not exceeding 10% is also discussed.

THE ''LIfe in Space'' project was funded in the wake of the Italian Space Agency's proposal for the development of a network of institutions and laboratories conceived to implement Italian participation in space astrobiology experiments. Of primary concern for this project is the study of the origin of life in the Universe, a focus that will promote investigation into prebiotic chemistry in various possible scenarios, whether in polar or nonpolar solvents (e.g., Titan's environment). Such results will link with study of the effects of simulated space conditions on possible chemical bio- signatures. The limits of life as we know it will be investigated in ground-based experiments with microorganisms that have already demonstrated their resistance to extreme environments on Earth and to real or simulated space conditions. The potential survival of microorganisms will also be examined with up-to-date molecular methods. The ability of some microorganisms to produce atmospheric and surface biosignatures when exposed to simulated conditions will be tested and compared with the possible existence of bio- signatures on potentially habitable exoplanets. Furthermore, the search for potentially habitable exoplanets, with space- based observational methods, will be optimized by way of dedicated climate models with the capacity to predict the detectability of atmospheric biosignatures for a broad range of planetary conditions. The project embraces the four most important topics in astrobiological research, as listed below, along with relevant contributions from the participating Italian institutions. Origins and evolution of organic compounds of biological significance in space (comets, asteroids, rocky planets, and moons); Prebiotic syntheses, origin of life, and early life; The limits of life and biological habitability: origin, evolution and adaptation of life in extreme environments on Earth and in space; Biomarkers for life detection in the Solar System and on exoplanets.

Chemical bonding in a set of six cuprous complexes with simple nitriles (CN-, HNC, HCN, CH3NC, and CH3CN) is investigated by means of a recently devised analysis scheme framed in density-functional theory and quantitatively singling out concurrent charge flows such as σ donation and π backdonation. The results of our analysis are comparatively assessed against qualitative models for charge redistribution based on the popular concepts of octet rule and resonance structures, and the relative importance of different charge-flow channels relating to σ donation, π back-donation, polarization, and hyperconjugation is discussed on a quantitative basis.

An integrated environment for the analysis of chemical bonding based on immersive virtual reality is presented. Using a multiscreen stereoscopic projection system, researchers are cast into the world of atoms and molecules, where they can visualize at a human scale the electron charge rearrangement (computed via state-of-the-art quantum-chemical methods) occurring on bond formation throughout the molecular region. Thanks to specifically designed features, such a virtual laboratory couples the immediacy of an immersive experience with a powerful, recently developed method yielding quantitative, spatially detailed pictures of the several charge flows involved in the formation of a chemical bond. By means of two case studies on organometallic complexes, we show how familiar concepts in coordination chemistry, such as donation and back-donation charge flows, can be effectively identified and quantified to predict experimental observables. © 2018 Wiley Periodicals, Inc.

A gas-phase nitrogen-nitrogen noncovalent interaction has been unveiled in the nitroethane-trimethylamine complex in an environment free from solvent and matrix effects using rotational spectroscopy in supersonic expansion. Different quantum chemical models (NOCV/CD and NBO) agree in indicating that this interaction largely prevails over the C-H⋅⋅⋅O and C-H⋅⋅⋅N hydrogen bonds. Furthermore, a SAPT analysis shows that electrostatic and dispersion interactions play a comparable role in stabilizing the complex. The conformational landscape exploration and stationary points characterization have been performed using state-of-the-art quantum-chemical computations providing significant insights on structure determination.

Through an analysis of eighty tetrahedral and square-planar metal carbonyls of general formula [M(CO)(L0)(L)2] including newly synthesized chlorocarbonyl rhodium complexes with chelating atropoisomeric diphosphanes, we show how coordination geometry can switch the carbonyl stretching frequency into a selective probe of the r-donor and p-acceptor abilities of the ligands. We thus provide a framework whereby the r-donation and p-backdonation constituents of the Dewar–Chatt–Duncanson model can be quantitatively predicted through spectroscopic data on coordinated CO moieties and vice versa.

The relation between spectroscopic observables and the detailed metal-ligand bonding features in chelation complexes is addressed using both experimental and state-of-the-art theoretical and computational methods. We synthesized and characterized a set of six nickel dicarbonyl complexes of general formula [Ni(CO)2(PP)], where PP is an atropoisomeric chelating diphosphine ligand. The analysis of the obtained experimental data and the basicity and oxidative potentials of the free ligands suggests a close relation between the donor ability of the chelating ligand and the carbonyl stretching frequencies observed in the complexes. We then use theory to unravel the detailed mechanisms of chelation-bond formation in terms of partial charge flows between the molecular orbitals of the fragments. By extending the promising, recently published natural orbitals for chemical valence/charge displacement (NOCV/CD) analysis scheme we provide a thorough, quantitative description of the several charge fluxes following the metal-ligand bond formation and demonstrate that the carbonyl stretching frequencies in the considered complexes selectively respond to the σ-donation charge flow from the phosphorus lone pairs of the ligands, with the frequency shift being in quantitative correlation with the extent of the ligand-to-metal charge transfer.

Thermal rate coefficients for the astrochemical reaction C + CH

Foundations and structure of the building blocks of GEMS, the ab initio molecular simulator designed for implementation on the EGEE computing Grid, are analyzed. The impact of the computational characteristics of the codes composing its blocks (the calculation of the ab initio potential energy values, the integration of the dynamics equations of the nuclear motion, and the statistical averaging of microscopic information to evaluate the relevant observable properties) on their Grid implementation when using rigorous ab initio quantum methods are discussed. The requests prompted by this approach for new computational developments are also examined by considering the present implementation of the simulator that is specialized in atom diatom reactive exchange processes. © 2010 Springer Science+Business Media B.V.

The chemistry of superheavy elements (Z ≥ 104) is actively investigated in atom-at-a-time experiments of volatility through adsorption on gold surfaces. In this context, common guidelines for interpretation based on group trends in the periodic table should be used cautiously, because relativistic effects play a central role and may cause predictions to fall short. In this paper, we present an all-electron four-component Dirac-Kohn-Sham comparative study of the interaction of gold with Cn (Z = 112), Fl (Z = 114), and Uuo (Z = 118) versus their lighter homologues of the 6th period, Hg, Pb, and Rn plus the noble gas Xe. Calculations were carried out for Au-E (E = Hg, Cn, Pb, Fl, Xe, Rn, Uuo), Au7- and Au20-E (E = Hg, Cn, Pb, Fl, Rn) complexes, where Au7 (planar) and Au20 (pyramidal) are experimentally determined clusters having structures of increasing complexity. Results are analysed both in terms of the energetics of the complexes and of the electron charge rearrangement accompanying their formation. In line with the available experimental data, Cn and more markedly Fl are found to be less reactive than their lighter homologues. On the contrary, Uuo is found to be more reactive than Rn and Xe. Cn forms the weakest bond with the gold atom, compared to Fl and Uuo. The reactivity of Fl decreases with increasing gold-fragment size more rapidly than that of Cn and, as a consequence, the order of the reactivity of these two elements is inverted upon reaching the Au20-cluster adduct. Density difference maps between adducts and fragments reveal similarities in the behaviour of Cn and Xe, and in that of Uuo and the more reactive species Hg and Pb. These findings are given a quantitative ground via charge-displacement analysis.

Golden fullerenes have recently been identified by photoelectron spectra by Bulusu et al. [S. Bulusu, X. Li, L.-S. Wang, X. C. Zeng, PNAS 2006, 103, 8326–8330]. These unique triangulations of a sphere are related to fullerene duals having exactly 12 vertices of degree five, and the icosahedral hollow gold cages previously postulated are related to the Goldberg–Coxeter transforms of C20starting from a triangulated surface (hexagonal lattice, dual of a graphene sheet). This also relates topologically the (chiral) gold nanowires observed to the (chiral) carbon nanotubes. In fact, the Mackay icosahedra well known in gold cluster chemistry are related topologically to the dual halma transforms of the smallest possible fullerene C20. The basic building block here is the (111) fcc sheet of bulk gold which is dual to graphene. Because of this interesting one-to-one relationship through Euler's polyhedral formula, there are as many golden fullerene isomers as there are fullerene isomers, with the number of isomers Nisoincreasing polynomially as (Formula presented.)). For the recently observed (Formula presented.), (Formula presented.), and (Formula presented.) we present simulated photoelectron spectra including all isomers. We also predict the photoelectron spectrum of (Formula presented.) . The stability of the golden fullerenes is discussed in relation with the more compact structures for the neutral and negatively charged Au12to Au20and Au32clusters. As for the compact gold clusters we observe a clear trend in stability of the hollow gold cages towards the (111) fcc sheet. The high stability of the (111) fcc sheet of gold compared to the bulk 3D structure explains the unusual stability of these hollow gold cages.