Study Of H+HD?H₂+D Reaction And N₂O VUV Photodissociation By Crossed Molecular Beam-Time Sliced Velocity Map Imaging Method

In this thesis,a new high-resolution crossed molecular beam apparatus using time-sliced velocity map ion imaging technique has been constructed,tested and optimized.Through a special design,different types of the source beams can be mounted and the crossing angle can be changed in a wide range of angles.The high-vacuum condition is obtained to decrease the background noise with a multi-stage differential pump structure,and the high-resolution detection system provides an important basis for the studying of state-to-state fundamental reaction dynamics.By using this apparatus,the state-to-state scattering dynamics of H+HD?H2+D reaction has been studied in detail.The oscillatary structures of H2(v=0,j=1,3)around the forward scattering direction are observed experimentally for the first time.Important dynamic imformation of reaction transition state has been obtained by combining with the accurate quantum mechanical calculation.Also,the study of photodissociation dynamics of N2O in vacuum ultraviolet region is carried out.The structures of intermediate states and the couplings between excited electronic states are deduced.Gas-phase chemical reactions are scattering processes of atoms and molecules.Because the fine angular distribution(eg.Oscillation structures)of the product in a specific quantum state contains some quantum interference effects from the scattered partial waves,it plays an important role in studying the quantum effects in chemical reactionos.The H+H2 reaction and its isotopic analogs are the simplest chemical reactions in nature,and have served as the most important benchmark systems in the field of chemical reaction dynamics.Due to the relatively small differential cross section and the limited experimental resolution,whether or not the fine structure on the angular distribution of the product exists in this reaction and how it behaves have not been supported by experimental results for a long period of time.In this thesis,the reaction dynamics of H+HD?H2+D under the collision energy of 1.35 eV are studied by this new crossed molecular beam apparatus.The rotational state resolved differential cross section is obtain by using time-sliced ion velocity map imaging technique with a near-threshold(1 + 1')resonance enhanced multiphoton ionization method.The oscillation structures of H2(v=0,j=1,3)products around the forward scattering direction in the differential cross section are observed.Furthermore,the detailed information on reaction transition states and intermediates corresponding to the forward scattering products are obtained by analyzing the oscillation structures.It is clearly illustrated that the forward scattering signals are mainly derived from the contributions of the partial waves around J=28 with an accurate quantum mechanical calculation.Interesting,the oscillations around the forward scattering direction in H+HD?H2+D reaction share many similarities with the optical corona phenomenon in atmosphere.In addition to molecular scattering process,the photolysis of gas phase molecules is of great significance in atmospheric and combustion chemistry.N2O plays an important role in atmospheric ozone depletion and global warming and the photodissociation process in stratosphere is a main sink of N2O.So,we investigated photodissociation dynamics of N2O in 124?134 nm and 142?149 nm regions combining a tunable vacuum ultraviolet source.Ion images of O(1S0)and O(3PJ=2,1,0)are observed.Then,the total kinetic energy distributions,branching ratios and angular disbributions of products are derived.In 124?134 nm region,the analysis for O(3PJ=2,1,0)+ N2(B3?g)channel reveals that there could be a strong coupling between the singlet D(1?+)and a triplet 3?v state.For the O(1S0)+ N2(X1?g+)and O(3PJ)+ N2(A3?u+)channels,the results show that the photodissociation processes are primarily governed by a parallel dissociation in a linear geometry,while the N2 products in vibrational excited states are very likely formed via a more bent transition state.In 142?149 nm region,O(1S0)+ N2(X1?g+)and O(3PJ = 2,1,0)+ N2(A3?u+)channels are possibly formed via the nonadiabatic couplings between the C(1?)and D(1?+)states or between C(1?)and A(1?-)states,which give rise to high vibrational excited N2 products.The ? values and the rotational profiles of N2 suggest a bent transition state plays an important role in the formation of the high vibrational excited channels.