Theoretical Studies Of Reaction Dynamics On XH₂O^-and Construction Of A Crossed Beam Apparatus With Multi-channel Rydberg-tagging Time-of-flight Detection

Molecular reaction dynamics is the frontier of chemistry to study the chemical reactions at atomic level.In Born-Oppenheimer framework,we can construct the po-tential energy surface?PES?of the target system by fitting a large number of electronic structure calculations and then classical and quantum dynamics calculation are applied to acquire the information of reaction,such as integral or differential reaction cross section,resonance and vibration spectrum,etc.Experimentally,the experimental tech-niques represented by the crossed molecular beam enable us to accurately measure a chemical reaction and obtain the experimental information such as the scattering angle distribution and the translational energy distribution of the products.The subject of the thesis is about theoretical and experimental reaction dynamics.In theoretical part,we construct the PESs of the following anion systems:F?H₂O?^-,OH₃^-,F?H₂O?^-ICH₃,and focus on the dynamics of systems.The fundamental invari-ents neural network?FI-NN?is the optimal choice for the construction of PES at present,where the fundamental invarients are used to describe the molecular structure with ex-change symmetry and the neural network is used to fit a large number of electronic structure data.The equilibrium geometries of anions are similiar to the corresponding neutral tran-sition states,so the photodetachment of anion can be used to detect the PES near the neural transition states.For F?H₂O?^-system?we constructed the accurate PES based on CCSD?T?method,and simulated the anion photoelectron spectrum of the system using time-dependent quantum wavepacket method.Our results verified the previous experimental and theoretical work of the system.The Feshbach resonances in pho-todetachment is discussed,and the resonance mechanism of anion photodetachment is proved to be consistent with that of neutral scattering.In addition,we also found the shift of peaks in photoelectron spectrum caused by isotope substitution,which indicated the spectator role of OH bond of FHOH-in photodetachment.OH₃^-is a typical four-atom anion-molecular reaction.We report an accurate full-dimensional PES of OH₃^-.The PES was constructed by fitting 55406 ab inito energies from the CCSD?T?/aug-cc-pVTZ level of theory with FI-NN approach,resulting in an extremely small fitting error of 0.52 meV.Extensive quasiclassical trajectory?QCT?simulations were carried out on the PES to investigate the proton transfer dynamics?OH^-+D₂?D^-+ HOD?.The product D-translational energy distribution and angular distribution were calculated and compared with previous experimental measurements,in which reasonably good agreement has been achieved.The angular distribution at a high collision energy exhibits an exclusively forward scattering peak,indicating the direct stripping mechanism at high energies.With the decrease of collision energy,the reaction shows a predominantly forward scattering feature,with very small sideways and backward scattering amplitudes,revealing combined mechanisms from direct ab-straction with short reaction time and complex-forming process with long reaction time.In the past decades,the bimolecular nucleophilic substitution reaction?S_N2?,rep-resented by X-+CH₃Y?CH₃X+Y-in the gas phase,has been extensively studied and the microsolvation method is an effective way to extend the gas phase research ex-perience to real reactions in liquid phase.In this paper,the full-dimensional PES of the microsolvation system F?H₂O?-+ICH₃ was constructed based on the double-hybrid functional XYGJ-OS.With the fitting techniques of spatial segmentation and energy expansion,the accuracy of the PES is effectively improved.Based on the PES,QCT calculation was carried out on the microsolvation reaction,and the dynamical reasons for the suppressed reactivity and the suppressed product solvated I-were pointed out.In addition,the branching ratio of important channels at 0.3 eV and 1.5 eV collision energy was calculated and the structure information of the long-life complex was revealed.The development of experimental instruments has always promoted the field of chemical dynamics.We report the construction of a crossed molecular beam appratus with a 15-channel hydrogen atom Rydberg time-of-flight spectrum detection.The appa-ratus can achieve the cross angle as small as 15 degree,and thus can be used to study on the cold chemistry of elementary reactions.We have done the initial test of the appara-tus with the photodissociation of CH₄ and the F+H₂ reaction.We used the H fragment angle distribution of CH₄ at 121.6 nm to to calibrate the detectors.In addition,we ap-plied the apparatus for the detection of H radical intermediates in the methane catalytic conversion.For the first time,H radicals were directly detected experimentally,which helps to reveal the mechanism information of methane catalytic conversion.