Investigations On The Reaction Dynamics Of The Atomic Oxygen Radical Anion (O~-) With Several Small Organic Molecules

The reactions between atomic oxygen radical anion (O) and molecules play important roles in many fields, such as ionospheric chemistry, combustion chemistry, synthesis of novel anions, chemical ionization mass spectrometry (CIMS), catalysis, and so on. For example, the concentrations of the O3-, OH-, NO3-, and CO3- in the ionosphere are related to the reactions involving O-; from the perspective for the synthesis of organic reactive intermediates, the halogen substituted carbene anion can be produced from the reactions of O- with corresponding halogen substituted methane, while the vinylidene anion (CH2=C-) can be prepared through the reaction between O-and ethylene. Moreover, studying the reactions between O- (H2O)n and molecules will give insights into exploring the mechanisms of the liquid phase chemical reactions.The reactions of O with molecules have been extensively investigated with flowing afterglow (FA), selected ion flow tube (SIFT), crossed beams apparatus, etc. The rate coefficients and branching ratios can be measured by employing the FA and SIFT apparatus, while the differential cross sections, energy distributions, and angular distributions for the products should be obtained through using the crossed beams technique. On the contrary, only a few of theoretical and computational studies have been performed on the reactions of O-with molecules.In this dissertation, we mainly utilize various theoretical and computational methods to investigate the reaction mechanisms and dynamics between O and small organic molecules. Methyl fluoride (CH3F), acetonitrile (CH3CN), and ethylene (C2H4) are chosen as our objects. In addition, we also have designed a novel anionic beam source, which will be used to study the anion-molecule reaction dynamics in the future. The key findings of this dissertation are summarized as follows.1. The static and dynamic reaction pathways involved in the reaction between O-and CH3F have been investigated. A special attention has been paid to the bimolecular nucleophilic substitution (SN2) reaction channel, that the intrinsic reaction coordinate (IRC) calculation, one-dimensional relaxed potential energy scan, and Born-Oppenheimer molecular dynamics (BOMD) simulations at the B3LYP/6-31+G(d,p) level of theory have been performed, respectively. As described in the classical reaction mechanism, the Sn2 transition state of [O…CH3…F]-links to F-+CH3O as products. However, the forward IRC calculation for this SN2 barrier surprisingly leads to an unexpected ion-dipole intermediate complex of HF…CHbO-The one-dimensional relaxed potential energy scan from this SN2 barrier along the elongation of the C…F distance with other coordinates optimized also shows the final products of HF and CH2O-. The BOMD simulations initiated at this SN2 barrier on the exit-channel potential energy surface (PES) reveal different dynamic reaction processes from the static reaction pathways. Two major dynamic reaction pathways are presented, one leads to HF+CH2O-, and the other corresponds to the SN2 reaction products of F and CH3O. The HF+CH2O- product channel seems to be more dominant than the SN2 pathway which produces F-+CH3O. Nevertheless, the CH2O- has not been observed in previous experiments as an anionic product. The potential factor for the vanishing of the CH2O- in experiments probably originates from the electron detachment process due to the negative electron affinity (EA) of CH2O. Furthermore, according to our BOMD simulations, the H abstraction channel is more dominant than the H2O production channel.2. The potential energy profile for the reaction between O- and CH3CN has been mapped at the G3MP2B3 level of theory. Geometries of the reactants, products, intermediate complexes and transition states involved in this reaction have been optimized at the B3LYP/6-31+G(d,p) level, and then the accuracy of their energies has been improved using the G3MP2B3 method. The potential energy profile is confirmed with the IPC calculations. Based on our calculations, the H2O+HCCN-production channel is the main one, while the CN-+CH3O production channel is very hard to occur. These two conclusions are consistent with previous experiments.3. The potential energy profile for the reaction of O-with C2H4 has been calculated at the G3MP2B3 level of theory, and thus, the static reaction pathways are obtained combined with IRC calculations. The dynamic reaction pathways after passing the [O…H…CH=CH2]- barrier for this reaction have also been investigated with BOMD simulations. The BOMD simulations initiated at this barrier on the exit-channel PES reveal several different types of dynamic reaction pathways leading to various anionic products. In particular, as the energy added on the transition vector of the [O…H…CH=CH2]-transition state increases remarkably, the OH-+CH2=CH production channel becomes dominant instead of the CH2=CHO-+H. As a result, unlike the static IRC profile, animated images are displayed and more extensive reaction mechanisms are illuminated for this reaction from the perspective of the dynamic reaction pathways.4. A new type of anionic beam source has been designed using the 12CaO·7Al2O3 (C12A7) material with effusive gas flow. Especially, an ion lens is utilized to improve the efficiency of the anion collection. For instance, the sulfur anion (S-) is prepared by using our anionic beam source. We expect that this anionic beam source will be applied to study the anion-molecule reaction dynamics and photoelectron spectroscopy of novel anions in the future.