Ultraviolet Photodissociation And Ultrafast Dynamics Of Halogen-containing Compounds

Molecular photodissociation is the most important and fundamental process in photochemistry and is also the most common phenomenon in the atmosphere.The dissociated products of halogen-containing compounds have potential effect on ozone depletion.Insight into the photodissociation dynamics of halogen-containing compounds has great significance in atmospheric chemistry and environmental protection.Photodissociation dynamics of halogen-containing compounds of n-C₅H₁₁Br,1,3 C₃H₆BrCl and C₃H₅OCl in the UV region have been investigated using ion velocity imaging coupled with resonance-enhanced multiphoton ionization techniques.Due to the excitation of repulsive potential energy surfaces by UV laser,C-Br bond fission in n-C₅H₁₁Br was a simple direct fast dissociation process.While,for 1,3-C₃H₆BrCl,it showed more complex dissociation channels due to the existence of Cl atom.The C-Br bond has undergone a direct breakage.Secondary dissociation of C₃H₆Cl radicals happened,which was induced by another UV photon absorption and lead to C-Cl bond fission.In the case of C₃H₅OCl,after absorption of a UV photon,a¹(n,Ï€^*) type electronic transition localized on the C=O chromophore can be ignited.This state interacted with ¹(n_Cl,σ_C-Cl^*) configuration localized on the C-Cl bond via avoided crossing and induced the prompt fission of C-Cl bond.The generated C₃H₅O radicals underwent a secondary dissociation producing CO fragments.The CO images displayed an isotropic spatial distribution.A stepwise dissociation has been displayed in the ultraviolet dissociation of C₃H₅OCl.The predissociation dynamics of B Rydberg state of methyl iodide has been studied with femtosecond pump-probe technique coupled with time-of-flight mass spectroscopy at pump pulse of 400 nm and a probe pulse of 800 nm.The lifetime of B Rydberg state was determined to be about 1.57 ps,which is very consistent with the previous work.The results were interpreted as a multiphoton dissociative ionization processes.Our work provides further information about the Rydberg states of methyl iodide.