Estudi experimental i teòric de la dinàmica de les reaccions ió-molècula

Resumen

Iso-chloropropane dehydrohalogenation processes by alkali ion collisions (Li, Na and K) have been studied from a theoretical and an experimental point of view. Both methods have detected the following channels:(1): C(3)H(7)Cl + M(8)? [C(3)H(6)M](+) + HCl; (2): C(3)H(7)Cl + M(+)? C(3)H(6) + [HClM(]+); (3) :C(3)H(7)Cl + M(+)? C(3)H(7) + MCl(+), where M represents the alkali ion. The first two reactions are dehydrohalogenations while the third one is a C-Cl bond heterolytic dissociation producing the alkali metal halide and C3H7+. Their reaction dynamics has been studied experimentally by molecular beam techniques while the theoretical research was carried out mainly by an exploration of potential energy surface (PES), a statistic study using direct dynamics as well as a RRKM analysis over the characterized PES. EXPERIMENTAL PART The described processes were studied using an octupolar radiofrequency-guided ion beam apparatus (RF-GIB) built in our lab. The alkali ions and iso-chloropropane in gas phase collide inside of octupolar reaction chamber at low pressures conditions where the reaction products are guided by a set of einzels lenses toward a mass spectrometer identifying the produced fragments. The obtention of the reactive cross section dependence as a function of collision energy for each channel and ion is the objective of this procedure. THEORETICAL PART The characterization of the PES, quasiclassical dynamics and RRKM study for the three alkali ions were performed in the theoretical part. The PES exploration and the possible reaction mechanisms was calculated by quantum chemistry using GAMESS 2008 package at MP2 level. The dynamics simulation was performed by Venus/NWChem, running on the fly classical trajectories. This software solves the classical equations of motion using the potential energy obtained from chemistry calculations, with the aim to calculate reactive cross sections. The visualization of pathways and a vibro-rotational analysis complete the dynamics study. Finally, the RRKM study allows to obtain a Kinetic Monte Carlo simulation. This model gives information about the several steps of the whole mechanism of the system and it complements the provided data by experimentation and the “on the fly” dynamics.