State-to-State Dynamics Study On The F/Cl+H₂/HD?V=1? Reactions

One of the most intriguing aspects of reaction dynamics is to study mechanism of chemical reactions with reagent in a certain quantum state. Development of laser technique brings a new era to us, which can not only help to detect the product but also control the reagent in a specific quantum state.Hydrogen is the most abundant element in the universe. Although chemical reactions involving hydrogen had attracted much attention, most of these studies were focused on the ground state due to technical difficulty of H2 molecules vibrational excitation. It is challenging to carry out the experimental study of reaction dynamics involving vibrationally excited H2 molecules.In this thesis, I participated in developing a single-longitudinal mode and high power nanosecond laser system. Combined this laser system with the high resolution time-of-flight Rydberg tagging apparatus, more than 13% population transfer from v=0 to 1 of H2 was demonstrated with the scheme of stimulated Raman Pumping in the crossed molecular beam experiment. These results provided an opportunity to study reaction dynamics involving vibrationally excited hydrogen molecules.Reaction resonances were firstly found in the state-to-state dynamics study of Cl+HD(v=1, j=0)?DCl+H reaction. The reaction of Cl+HD has always appeared to proceed via a direct abstraction mechanism, with no clear signature of reaction resonances. In this study, oscillatory structures were detected at the backward direction from the collision energies of 1.9 to 4.9 kcal/mol. The structures attributed to reaction resonances are related to the states trapped in the peculiar H-DCl(v'=2) vibrationally adiabatic potential well by the calculations. We anticipate that similar resonance phenomena may occur in a broad range of chemical reactions involving vibrationally excited molecules.At the collision energy of 0.52 kcal/mol, the forward scattering peak of the HF(v'=2) product, which was attributed to Feshbach resonances in the F+H2(v=0, j=0) reaction, disappeared in the crossed molecular beam study of the F+H2(v=1,j=0)?HF+H. Quantum dynamics calculations reveal that the reaction occurs via likely a direct abstraction mechanism, not via long-lived reactive resonances from the collision energies of 0.4 to 2.0 kcal/mol. The reaction will have no chance to occur via these resonance states trapped in the peculiar H-HF(v'=4) vibrationally adiabatic potential well for the vibrationally excited reaction.