OCS Photodissociation Dynamics And F+CH₄?v₃=2?Reaction By Time Sliced Velocity Map Ion Imaging Method

The molecular scattering process can generally be divided into collisions and semi-collision processes(such as photolysis reactions)between atoms and molecules.Microscopic reaction kinetics is to study the dynamic properties in a single collision,such as the energy exchange between particles,the formation mechanism and lifetime of reaction complexes,as well as the velocity and angular distribution of scattering products.In this thesis,the photodissociation dynamics of carbonyl sulfide(OCS)has been investigated using the high sensitivity time-sliced velocity map ion imaging technique combined with the tunable vacuum ultraviolet(VUV)laser light.In addition,we investigated the photodissociation dynamics of the D-atom channel from DNCO photolysis using the H-atom Rydberg tagging time-of-flight technique.Besides,using the infrared laser generated by the optical parametric oscillator/optical parametric amplifier(OPO/OPA),we carried out study on the state-to-state scattering dynamics of elementary chemical reactions F+CH4?HF+CH3 in detail.OCS plays an important role in the Earth's global atmospheric sulfur cycle.Atomic sulfur released from the photolysis of OCS in the stratosphere could react to form sulfate,making OCS the dominant non-volcanic source of stratospheric sulfate aerosols(SSAs).SSAs destroy stratospheric ozone and influence Earth's radiative balance.We use the molecular beam apparatus with a time-sliced ion imaging detector to study the photodissociation dynamics of OCS in the 140-160 nm region.Images of atomic sulphur ion products(S+)were obtained directly,from which two product channels:S(1SJ=0)+CO(X1?g+)and S(3PJ-2,1,0)+CO(X1?g+)were identified.Besides,detailed and rich information about the dissociation dynamics such as speed distributions and vibrational resolved angular distributions as well as branching ratios between different vibrational states were reported.With the analysis of the experimental results,we conclude that the S(1SJ=0)+CO(X1?g+)channel is dominated by the 1?+-1?+ parallel transition process.Meanwhile,two possible triplet dissociation mechanisms should give rise to the formation of S(3PJ=2,1,0)+CO(X1?g+)products mainly involving three states,i.e.13A'/13A"(3?)and 23A"(3?-).The results are beneficial for the understanding of the photodissociation dynamics of OCS in the VUV region.HNCO and its isotopic variants play an important role in combustion and atmospheric chemistry.In addition,the photodissociation of HNCO can serve as a benchmark for more complex systems.The investigation on the photodissociation of deuterated isocyanic acid(DNCO)will be an important complement to the research on the dynamics of this system.In this work,photodissociation dynamics of the D-atom channel from DNCO photolysis between 133-137 nm was studied using the H-atom Rydberg tagging time-of-flight technique.The D-atom elimination channel was detected and the corresponding product translational energy distributions and angular distributions have been determined.Besides,three product channels and at least four dissociation pathways have been characterized.A chemical reaction is usually driven by energy or increasing temperature.The effect of energy in different degrees of freedom,such as translational energy,vibrational excitation,rotational excitation etc.,in driving a chemical reaction is different and the dynamics of the reaction is also dependent on the types of the driving energy.The influence of vibration excitation of reactants on chemical reactions has always been a subject of great concern.In this thesis,by using crossed-beam and time-sliced velocity map imaging techniques,we investigate important elementary chemical reaction F+CH4(v3=0,2)?HF+CH3 to explore how the vibrational excitation of reagents affects the chemical reactivity and the reaction dynamics.The production of CH3(122/322)was observed for the first time in the cross-beam experiment,which enriched the vibrational spectra of methyl radicals.The effects of CH4(v3=2)over-frequency vibrational excitation on products with different vibrational states were revealed.Combined with theoretical calculations,the assignments of the products and the specific path and mode of energy transfer during the reaction process of CH4(v3=2)over-frequency vibrational excitation were clarified.