130,556 research outputs found
CHAPTER 3: Gas-phase Prebiotic Chemistry Driven by Ultraviolet Photolysis of Simple Molecules
No full textThe 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
Non-Born-Oppenheimer MCTDH calculations on the confined H2+ molecular ion
No full textA 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 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 energy levels have been generated. The initial time evolution of the time-dependent orbitals is also shown
Microscopic Branching Processes: The O + O-2 Reaction and Its Relaxed Potential Representations
No full textAn analysis of the O3DMBE 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 = O 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. © 2009 Wiley Periodicals, Inc
A program for performing exact quantum dynamics calculations using cylindrical polar coordinates : a nanotube application
No full textA program that uses the time-dependent wavepacket method to study the motion of structureless particles in a force field of quasi-cylindrical symmetry is presented here. The program utilises cylindrical polar coordinates to express the wavepacket, which is subsequently propagated using a Chebyshev expansion of the Schrödinger propagator. Time-dependent exit flux as well as energy-dependent S matrix elements can be obtained for all states of the particle (describing its angular momentum component along the nanotube axis and the excitation of the radial degree of freedom in the cylinder). The program has been used to study the motion of an H atom across a carbon nanotube
AN INNOVATIVE COMPUTATIONAL COMPARISON OF EXACT AND CENTRIFUGAL SUDDEN QUANTUM PROPERTIES OF THE N+N2 REACTION
No full textA new Gaussian MCTDH program: implementation and validation on the levels of the water and glycine molecules
No full textWe 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.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. © 2014 AIP Publishing LLC
The O + O2 reaction : quantum detailed probabilities and thermal rate coefficients
No full textThe detailed quantum probabilities of the O + O2 reactive system have been computed at zero total angular momentum using the time-independent quantum program ABC thanks to the restructuring of the code and its implementation on the EGEE production Grid. Their main features are discussed and out of them J-shifting thermal rate coefficients have been computed to compare with the experiment and quasiclassical trajectory results over a wide range of temperatures. © 2009 Springer-Verlag
On a Coupled System of Shallow Water Equations Admitting Travelling Wave Solutions
No full textWe consider three inviscid, incompressible, irrotational fluids that are contained between the rigid walls y = −h and y = h +H
and that are separated by two free interfaces. 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
Quantum stereodynamics for the two product channels of the F+HD reaction from complete scattering matrix in the stereodirected representation
No full textFor the two exit arrangements of the F + HD reaction, the full scattering matrix is obtained by exact quantum dynamics on an accurate potential energy Surface. The S matrix is expressed in the stereodirected representation, for the first time, for all channels of a triatomic reaction. We analyze a collision energy where the dominant reaction mechanism is direct and a total angular momentum J = 0. It is found that the introduction of steric quantum numbers (correlated in the vector model to the angles measuring directions of approaching reactants and of separating products) provides a sharp description of stereodynamical features for both exit channels
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