The photolysis of stable simple molecules by means of solar ultraviolet photons is known to be the first step in the chemistry of planetary atmospheres. The transient species produced in this way can react and form more complex molecules that are normally present in trace amounts. Trying to tackle the problem associated with the massive organic system that allegedly preceded the emergence of life on Earth according to the abiotic origin of life theory, we consider here the possibility that prebiotic chemistry on Earth started in its upper atmosphere. A proof-of-concept of this scenario can be provided by investigating the atmospheric chemistry of other planets and moons. In particular, if one searches for good test cases in our Solar System, the atmosphere of Titan stands out for its rich organic chemistry. In this chapter, our comprehension of the chemistry leading to N-rich organic molecules and macromolecules as made possible by resorting to a multidisciplinary approach based on photochemical models and dedicated laboratory experiments will be illustrated. The focus will be on neutral bimolecular reactions leading to nitriles, imines and other organic N-bearing molecules which can react further in the upper atmosphere of Titan up to the formation of macromolecules. Nitriles, imines and N-containing macromolecules are known as possible precursors of amino acids and nucleobases once they come into contact with water.

How could life emerge on an originally inorganic Earth? This is the main question faced in the field of prebiotic chemistry. In order to solve this issue, two main, and not incompatible, hypotheses have been made. An endogenous synthesis one, based on the theory that building blocks of life were synthesized in the atmosphere of the early Earth and/or in primitive oceans, and an exogenous delivery one, according to which those building blocks were synthesized in space and then brought to Earth by comets and asteroids. In this contribution, based on state-of-the-art quantum chemistry computations, both hypotheses will be considered. First, possible gas-phase formation routes in the interstellar medium for two molecules of prebiotic interest will be investigated: glycolaldehyde (HOCH2CHO), the simplest sugar-related molecule, able to ease the formation of more complex sugars and formamide (H2NCHO), a possible precursor that might be able to link the appearances of metabolism and genetics. And then, thanks to a synergy between experimental and theoretical chemistry, a potential way of forming mercaptoacetaldehyde (HSCH2CHO), a possible prebiotic precursor of cysteine, will be explored in the peculiar conditions of the early Earths ocean.

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. Advantage has been taken of a flash pyrolysis experimental set-up with mass spectrometric detection, in which the brief residence time of the pyrolyzing mixture inside a short, resistively heated SiC tube allows the identification of the primary products of the decomposing species, limiting secondary processes. Dedicated electronic structure calculations of the relevant potential energy surface have also been performed and RRKM estimates of the rate coefficients and product branching ratios up to 2,000 K are provided. Both electronic structure and RRKM calculations are in line with previous determinations. According to the present study, the H2O elimination channel leading to 1-butene is more important than previously believed. In addition to that, we provide experimental evidence that butanal formation by H2 elimination is not a primary decomposition route. Finally, we have experimental evidence of a small yield of the CH3 elimination channel.

A. Rimola, N. Balucani, C. Ceccarelli D. Skouteris, P. Ugliengo 1 Departament de Química, Universitat Autònoma de Ba rcelona, Bellaterra, 08193, Spain. 2 Dipartimento di Chimica, Biologia e Biotecnologie, Università di Perugia, Perugia, 06123, Italy 3 Univ. Grenoble Alpes, CNRS, Institut de Planétologi e et d’Astrophysique de Grenoble (IPAG), Grenoble, 38000, France . 4 Scuola Normale Superiore, Pisa, 56126, Italy 5 Dipartimento di Chimica and Nanostructured Interfa ces and Surfaces (NIS), Università degli Studi di Torino, Torino, 10125, Italy. albert.rimola@uab.cat

Context. Modern versions of the Miller-Urey experiment claim that formamide (NH2CHO) could be the starting point for the formation of metabolic and genetic macromolecules. Intriguingly, formamide is indeed observed in regions forming solar-type stars and in external galaxies.Aims. How NH2CHO is formed has been a puzzle for decades: our goal is to contribute to the hotly debated question of whether formamide is mostly formed via gas-phase or grain surface chemistry.Methods. We used the NOrthern Extended Millimeter Array (NOEMA) interferometer to image NH2CHO towards the L1157-B1 blue-shifted shock, a well-known interstellar laboratory, to study how the components of dust mantles and cores released into the gas phase triggers the formation of formamide.Results. We report the first spatially resolved image (size similar to 9 '', similar to 2300 AU) of formamide emission in a shocked region around a Sun-like protostar: the line profiles are blueshifted and have a FWHM similar or equal to 5 km s(-1). A column density of N-NH2CHO = 8 x 10(12) cm 1 and an abundance, with respect to H-nuclei, of 4 x 10(9) are derived. We show a spatial segregation of formamide with respect to other organic species. Our observations, coupled with a chemical modelling analysis, indicate that the formamide observed in L1157-B1 is formed by a gas-phase chemical process and not on grain surfaces as previously suggested.Conclusions. The Seeds of Life in Space (SOLIS) interferometric observations of formamide provide direct evidence that this potentially crucial brick of life is efficiently formed in the gas phase around Sun-like protostars.

We present a method for calculating partition functions taking into account anharmonic contributions for systems involving both small-amplitude vibrations and hindered rotations. The Wang-Landau scheme is used in the first case, while two alternative schemes are used for hindered rotation based on imaginary time propagation and fitting of the exact energy levels as a function of quantum number. These two schemes are shown to be complementary in their ranges of applicability (in terms of the torsional rotational constant and the relevant potential). Partition functions for four different molecules are calculated and compared to simpler ones obtained using a harmonic model.

We present a calculation of the torsional potential of the three metallocenes of the iron group, that is, ferrocene, ruthenocene, and osmocene, calculated with the GAUSSIAN program suite. Both a variational method (through computation of the exact energy levels) and our Chebyshev imaginary time propagation method are used to calculate the hindered rotation partition function, demonstrating the efficiency of the Chebyshev scheme. The transition from a semirigid through a hindered rotor to the free rotor regime is demonstrated, and the effect of the hindered rotation (as opposed to a harmonic) treatment on the thermodynamics of metallocenes is demonstrated.

New insights into the formation of interstellar formamide, a species of great relevance in prebiotic chemistry, are provided by electronic structure and kinetic calculations for the reaction NH2 + H2CO -> NH2CHO + H. Contrarily to what previously suggested, this reaction is essentially barrierless and can, therefore, occur under the low temperature conditions of interstellar objects thus providing a facile formation route of formamide. The rate coefficient parameters for the reaction channel leading to NH2CHO + H have been calculated to be A = 2.6x10^{-12} cm^3 s^{-1}, beta = -2.1 and gamma = 26.9 K in the range of temperatures 10-300 K. Including these new kinetic data in a refined astrochemical model, we show that the proposed mechanism can well reproduce the abundances of formamide observed in two very different interstellar objects: the cold envelope of the Sun-like protostar IRAS16293-2422 and the molecular shock L1157-B2. Therefore, the major conclusion of this Letter is that there is no need to invoke grain-surface chemistry to explain the presence of formamide provided that its precursors, NH2 and H2CO, are available in the gas-phase.

We consider three inviscid, incompressible, irrotational fluids that are contained between the rigid walls y=−h1 and y=h+H and that are separated by two free interfaces η1 and η2. A generalized nonlocal spectral (NSP) formulation is developed, from which asymptotic reductions of stratified fluids are obtained, including coupled nonlinear generalized Boussinesq equations and (1+1)-dimensional shallow water equations. A numerical investigation of the (1+1)-dimensional case shows the existence of solitary wave solutions which have been investigated for different values of the characteristic parameters.

We report the main features of a new general implementation of the Gaussian Multi-Configuration Time-Dependent Hartree model. The code allows effective computations of time-dependent phenomena, including calculation of vibronic spectra (in one or more electronic states), relative state populations, etc. Moreover, by expressing the Dirac-Frenkel variational principle in terms of an effective Hamiltonian, we are able to provide a new reliable estimate of the representation error. After validating the code on simple one-dimensional systems, we analyze the harmonic and anharmonic vibrational spectra of water and glycine showing that reliable and converged energy levels can be obtained with reasonable computing resources. The data obtained on water and glycine are compared with results of previous calculations using the vibrational second-order perturbation theory method. Additional features and perspectives are also shortly discussed.

The development of an innovative computational strategy suited to provide an accurate quantum evaluation of the detailed properties of the N + N-2 exchange reaction has been undertaken by carrying out an extended theoretical study of such reaction. To this end exact and approximate quantum calculations (based on both time-independent and time-dependent techniques) of state-specific and state-to-state probabilities of the title reaction have been performed by considering values of the total angular momentum quantum number up to 20, values of total energy up to 2.3 eV and by making a combined use of both high throughput and high performance computing platforms. The comparison of the results obtained from calculations performed by taking into account the full Coriolis coupling of the allowed helicity states with those obtained when neglecting the Coriolis coupling or even a model energy shift treatment has allowed us to find out when a workflow managing the distribution of the jobs can replace exact treatments with approximate ones and for what type of properties this is possible.

The potential energy surface of the systems N(2D) + CH4 , C2 H4 , and C2 H6 have been investigated at B3LYP/aug-cc-pVTZ//CCSD(T)/aug-cc-pVTZ level in order to assist the interpretation of available experimental information very relevant for its implication for the chemical models of the atmosphere of Titan, and possibly of objects where both N2 and small hydrocarbons like methane are present, such as Triton and Pluto.

The computational core of the time dependent (TD) wavepacket program RWAVEPR has been implemented on a NVIDIA GPU of the GTX class. The TD program is a quantum wavepacket code that integrates the time-dependent Schrödinger equation for the generic atom-diatom reaction. In particular, the work has focused on the propagation procedure of the program, represented by the miham and lowpass routines, by implementing a fine grain model of parallelism on the GPU. Various features of the NVIDIA GPU have been exploited and different models of parallelism have been implemented and tested. Elapsed times and speed-ups for an atom-diatom chemical reaction have been calculated on the GPU and compared with the related CPU ones.

A multiconfiguration time-dependent Hartree method based on non-orthogonal coordinates has been developed. The method has been applied to the calculations of the properties of atomic and molecular systems beyond the Born–Oppenheimer approximation, treating electrons and nuclei on a similar footing. Example calculations have been performed on the confined H2+ ion, treated as a genuine three-particle system. With only two orbitals per degree of freedom to begin with, the confinement energy levels as well as the origin of the genuinely bound H2+ energy levels have been generated. The initial time evolution of the time-dependent orbitals is also shown.

An analysis of the O-3 DMBE potential energy surface is performed using unconventional contour maps. In this way alternative paths leading to the same products (microscopic branching) are singled out. The detailed J = 0 quantum probabilities and related mode selectivity and energy disposal obtained through an extensive computational campaign on the EGEE production Grid are interpreted in terms of the mentioned alternative reactive paths. (C) 2009 Wiley Periodicals, Inc. Int J Quantum Chem 110: 358-367, 2010

The dynamics of the H-displacement channels in the reaction N(2D) + C2H6 have been investigated by the crossed molecular beam technique with mass spectrometric detection and time-of-flight analysis at two different collision energies (18.0 and 31.4 kJ mol(-1)). From the derived center-of-mass product angular and translational energy distributions the reaction micromechanisms and the product energy partitioning have been obtained. The interpretation of the scattering results is assisted by new ab initio electronic structure calculations of stationary points and product energetics for the C2H6N ground state doublet potential energy surface. C-C bond breaking and NH production channels have been theoretically characterized and the statistical branching ratio derived at the temperatures relevant for the atmosphere of Titan. Methanimine plus CH3 and ethanimine plus H are the main reaction channels. Implications for the atmospheric chemistry of Titan are discussed.

The reaction between sulfur atoms in the first electronically excited state, S((1)D), and ethene (C(2)H(4)) has been investigated in a complementary fashion in (a) crossed-beam dynamic experiments with mass spectrometric detection and time-of-flight (TOF) analysis at two collision energies (37.0 and 45.0 kJ mol(-1)), (b) low temperature kinetics experiments ranging from 298 K down to 23 K, and (c) electronic structure calculations of stationary points and product energetics on the C(2)H(4)S singlet and triplet potential energy surfaces. The rate coefficients for total loss of S((1)D) are found to be very large (ca. 4 x 10(-10) cm(3) molecule(-1) s(-1)) down to very low temperatures indicating that the overall reaction is barrierless. From laboratory angular and TOF distributions at different product masses, three competing reaction channels leading to H + CH(2)CHS (thiovinoxy), H(2) + CH(2)CS (thioketene), and CH(3) + HCS (thioformyl) have been unambiguously identified and their dynamics characterized. Product branching ratios have also been estimated. Interpretation of the experimental results on the reaction kinetics and dynamics is assisted by high-level theoretical calculations on the C(2)H(4)S singlet potential energy surface. RRKM (Rice-Ramsperger-Kassel-Marcus) estimates of the product branching ratios using the newly developed singlet potential energy surface have also been performed and compared with the experimental determinations.