Un estudio teórico de las reacciones elementales: C + FH --- CF + H y O + FH --- OF + H

[spa] En el presente trabajo se realiza un estudio teórico de las reacciones del tipo átomo-molécula diatómica en las que interviene la molécula de fluoruro de hidrógeno, y los átomos de carbono y oxígeno. Comprende las dos partes esenciales que constituyen el estudio teórico de un proceso químico elemental, es decir, la caracterización del sistema en cuanto hace referencia a su comportamiento estático (superficies de potencial) y la obtención de resultados dinámicos. Con el fin de hacer factible la resolución del problema dinámico segun la Mecánica Cuántica, se ha abordado el estudio de las mencionadas reacciones en la aproximación monodimensional en la cual se mantiene fija la orientación del movimiento relativo de las dos especies reccionantes

Dehydrohalogenation and dehydration reactions of i‑C3H7Br and i‑C3H7OH by sodium ions studied by guided ion beam techniques and quantum chemical methods

Dehydrohalogenation and dehydration reactions of gas-phase i-C3H7Br and i-C3H7OH molecules induced by collision with Na+, all participants being in their electronic ground state, were studied experimentally in our laboratory using a radiofrequency-guided ion beam apparatus and covering the 0.10-10.00 eV center of mass (CM) energy range. In Na+ + i-C3H7Br collisions the formation of [C3H6-Na]+ and [HBr-Na]+ by dehydrohalogenation was observed and quantified, as well as that of the ion-molecule adduct [Na-i-C3H7Br]+ together with its decomposition products C3H7+ and NaBr. In Na+ + i-C3H7OH collisions the dehydration product [H2O-Na]+ was also found, while [C3H6-Na]+ was hardly detected. Moreover, the [Na-i-C3H7OH]+ adduct formation as well as its decomposition into C3H7+ and NaOH were also quantified. For all these processes, absolute reaction cross sections were measured as a function of the CM collision energy. From measured excitation functions, rate constants for the formation of [C3H6-Na]+, [HBr-Na]+, and [H2O-Na]+ at 303 K were obtained. Complementing the experiments, exhaustive ab initio structure calculations at the MP2 level of theory were performed, giving information on the most relevant features of the potential energy surfaces (PESs) where the dehydrohalogenation, dehydration, and decomposition reactions take place adiabatically for both collision systems. On these PESs different stationary points associated with potential energy minima and transition state barriers were characterized, and their connectivity was ensured using the intrinsic-reaction-coordinate method. The main topology features of the ab initio calculated PESs allowed a qualitative interpretation of the experimental data also exposing the role of the sodium ion as a catalyst in elimination reaction

Experimental and ab initio studies of the reactive processes in gas phase i-C3H7Br and i-C3H7OH collisions with potassium ions

Collisions between potassium ions and neutral i-C3H7Br and i-C3H7OH, all in their electronic ground state, have been studied in the 0.10 10.00 eV center of mass (CM) collision energy range, using the radiofrequency-guided ion beam technique. In K+ + i-C3H7Br collisions KHBr+ formation was observed and quantified, while the analogous KH2O+ formation in K+ + i-C3H7OH was hardly detected. Moreover, formation of the ion-molecule adducts and their decomposition leading to C3H7 + and either KBr or KOH, respectively, have been observed. For all these processes, absolute crosssections were measured as a function of the CM collision energy. Ab initio structure calculations at the MP2 level have given information about the potential energy surfaces (PESs) involved. In these, different stationary points have been characterized using the reaction coordinate method, their connectivity being ensured by using the intrinsic-reaction-coordinate method. From the measured excitation function for KHBr+ formation the corresponding thermal rate constant at 303 K has been calculated. The topology of the calculated PESs allows an interpretation of the main features of the reaction dynamics of both systems, and in particular evidence the important role played by the potential energy wells in controlling the reactivity for the different reaction channels

The reactivity of cyclopropyl cyanide in titan's atmosphere: a possible pre-biotic mechanism

Cyclopropyl cyanide and other simple nitriles detected in Titan's atmosphere could be precursors leading to the formation of organic macromolecules in the atmosphere of Saturn's largest satellite. Proposing a thermodynamically possible mechanism that explains their formation and supports experimental results represents a difficult challenge. Experiments done in the Atomic and Molecular Physics Laboratory at the University of Trento (AMPL) have studied the ion-molecule reaction between cyclopropyl cyanide and its protonated form, with reaction products being characterized by mass spectrometry. In addition to the expected ion-molecule adduct stabilized by non-covalent long-range interactions, in this work we prove that another distinct species having the same mass to charge ratio (m/z) of 135 is also produced. Moreover, from a previous study of the neutral cyclopropyl cyanide potential energy surface (PES) which shows a partial biradical character it has been possible to characterize the formation through the bimolecular reaction of a new covalent cyclic organic molecule. Calculations have been carried out at the ab initio Møller-Plesset (MP2) level of theory, ensuring the connectivity of the stationary points by using the intrinsic reaction coordinate (IRC) procedure. In order to characterize the reaction transition state, multireference calculations were done using a complete active space involving six electrons and six molecular orbitals [CAS (6 e, 6 m.o.)]. This study opens the possibility of exploring the formation of new organic molecules by gaseous phase ion-molecule interaction schemes, with such molecules having relevance in interstellar space and in astrobiology (and may be involved in prebiotic molecular evolution)

Theoretical characterization of transition state dynamical resonances in heavy-light-heavy reactions

The resonant reactivity of three elementary Heavy-Light-Heavy reactions is presented and discussed. Collinear reactivity, in which a vibrational adiabatic model is constructed, is used for a detailed analysis of resonance phenomena, which appear as a direct consequence of transition state metastable states in the strong interaction region of the potential energy surface. Their influence on the detailed mechanism of the elementary process is also discussed. The shape of the resonant peak, and the phase and the Argand plot of the S-matrix are used for a further characterization.Three-dimensional approximate calculations are used to test the evolution of the energy dependent structure present in detailed quantities when sums and integrations over all partial waves contributing to reaction are taken into account to obtain the usual averaged global quantities such as integral state-to-state cross sections

The role of Li+ ions in the gas phase dehydrohalogenation and dehydration reactions of i-C3H7Br and i-C3H7OH molecules studied by radiofrequency-guided ion beams techniques and ab initio methods

Gas phase reactive collisions between lithium ions and i-C3H7X (X = Br, OH) molecules have been studied under single collision conditions in the center of mass (CM) 0.01-10.00 eV energy range using a radiofrequency-guided ion beam apparatus. Mass spectrometry analysis of the products did show the presence of [C3H6-Li]+, [HX-Li]+, C3H7+, and C2H3+ as well as of the [Li-i-C3H7Br]+ adduct while [Li-i-C3H7OH]+ was hardly detected. For all these reactive processes, the corresponding cross sections have been measured in absolute units as a function of the CM collision energy. Quantum chemistry ab initio calculations done at the second orderM¨oller Plesset level have provided relevant information on the topology of the potential energy surfaces (PESs) where a reaction takes place allowing the characterization of the stationary points on the respective PESs along their reaction pathways. The connectivity of the different stationary points localized on the PESs was ensured by using the intrinsic reaction coordinate (IRC) method, confirming the adiabatic character of the reactions. The main topology features of the reactive PESs, in the absence of dynamical calculations, were used to interpret at the qualitative level the behavior of the experimental excitations functions, evidencing the role played by the potential energy barriers on the experimental dynamics of the reactions. Reaction rate constants at 303.2 K for different reactions have been calculated from measured excitation functions

Un estudio teórico de las reacciones elementales : C + FH --- CF + H y O + FH --- OF + H

En el presente trabajo se realiza un estudio teórico de las reacciones del tipo átomo-molécula diatómica en las que interviene la molécula de fluoruro de hidrógeno, y los átomos de carbono y oxígeno. Comprende las dos partes esenciales que constituyen el estudio teórico de un proceso químico elemental, es decir, la caracterización del sistema en cuanto hace referencia a su comportamiento estático (superficies de potencial) y la obtención de resultados dinámicos. Con el fin de hacer factible la resolución del problema dinámico segun la Mecánica Cuántica, se ha abordado el estudio de las mencionadas reacciones en la aproximación monodimensional en la cual se mantiene fija la orientación del movimiento relativo de las dos especies reccionantes

Un estudio teórico de las reacciones elementales : C + FH --- CF + H y O + FH --- OF + H

En el presente trabajo se realiza un estudio teórico de las reacciones del tipo átomo-molécula diatómica en las que interviene la molécula de fluoruro de hidrógeno, y los átomos de carbono y oxígeno. Comprende las dos partes esenciales que constituyen el estudio teórico de un proceso químico elemental, es decir, la caracterización del sistema en cuanto hace referencia a su comportamiento estático (superficies de potencial) y la obtención de resultados dinámicos. Con el fin de hacer factible la resolución del problema dinámico segun la Mecánica Cuántica, se ha abordado el estudio de las mencionadas reacciones en la aproximación monodimensional en la cual se mantiene fija la orientación del movimiento relativo de las dos especies reccionantes

The prediction of chemical reactivity from first principles: Collision and reaction dynamics

Aquest treball fa una revisió de mesures experimentals i càlculs teòrics sobre la dinàmica de col·lisions i reaccions moleculars. Els experiments se centren en col·lisions, a energies intermèdies, que involucren sistemes del tipus ió-àtom i iómolècula, per les quals es mesuren seccions eficaces totals, estat a estat, així com aquelles que discerneixen les diferents contribucions del moment angular d'espín. Els resultats obtinguts s'interpreten satisfactòriament en termes d'acoblaments no adiabàtics entre els diferents estats electrònics dels sistemes col·lisionants. Els càlculs teòrics utilitzen la metodologia quasiclàssica, així com metodologies mecanoquàntiques recentment desenvolupades, tant aproximades com exactes. S'han obtingut resultats totalment convergits per sistemes tipus, mentre que s'han analitzat, de manera detallada i extensiva, les característiques dinàmiques de sistemes triatòmic, tetraatòmic i pentaatòmic

Electròlisi i transport d'ions

Electròlisi d'una dissolució d'àcid sulfúric en una cel·la de Hittorf i anàlisi dels processos de transport i balanços de matèria dels ions en dissolució.Ajut PMID convocatòria 2010 per a l'edició i elaboració de material audiovisua