The Design And Setting Up Of The Universal Crossed Beam Apparatus And The Photodissociation Study Of OCS In VUV Region

The study of elementary reactions is very important to chemistry.Crossed molecular beam method is a powerful way to study the dynamics of elementary reactions.It is meaningful to the studies of atmospheric chemistry,astrochemistry and combustion chemistry.The author designed a universal crossed molecular beam apparatus during the master study.The apparatus employs mass spectrometry with photoionization.The detection has very high sensitivity.The apparatus has two rotatable source chambers,a scattering chamber and a mass spectrometer chamber.It can achieve large angular range detection using the mass spectrometer.After some modifications,it can also be equipped with ion optics.The background noise can be significantly decreased with a multi-stage differential pumping setup.The mass spectrometer chamber can be cooled by liquid nitrogen and cold.In this way,very good vacuum condition can be achieved.The author took part in all the manufacturing processes,from drawing to leak testing.By efficiently communicating with engineers,the chamber was successfully manufactured and very well match the request of the experiment.Heating treatment was conducted to reduce hydrogen and decrease the background.At the same time,the concentricity of the two rotatable source chambers is very high,so the area of the beam crossed can be well defined.By the testing,the main chamber can reach high vacuum,and the mass spectrometer chamber can reach ultra-high vacuum after heating and cooling by the liquid nitrogen.Besides setting up the apparatus,the author also studied the photodissociation dynamics of OCS in vacuum ultraviolet region.OCS is an important greenhouse gas.It is also a significant precursor in sulfur cycles.It plays an important role in atmospheric chemistry.So we investigated photodissociation dynamics of OCS in 126-129nm regions combining a tunable vacuum ultraviolet source.We get the ion images of S(³P_J=2,1,0),S?¹D₂? and S?¹S₀?.Then we get the total kinetic energy distributions,branching ratios and angular distributions of the products.The results suggest that the S(³P_J=2,1,0)+CO?A³??product channel is formed through the dissociation process after the excitation to the?3¹?⁺?excited state.Strong nonadiabatic coupling also plays an important role in the formation of other three channels.