Reactions of short-lived species in a flowing afterglow
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
A steady-state flowing afterglow method has been used to measure rate coefficients for a number of positive ion-molecule reactions. A description of the technique and the method of data analysis is given. Rate coefficients for proton transfer from H₃⁺ to neutral species XCN have been found to be in good agreement with those predicted by the ADO (or AQO) theory for X= H, CH₃ , Cl, and CN. For X= Br, I, the experimental rate coefficients were lower than predicted by the ADO theory by 37% and 48% respectively. Rate coefficients have been measured for a number of reactions relating to the formation and destruction of sulphur-containing molecules and of hydrogen cyanide in interstellar gas clouds. These new laboratory measurements produce no major changes in mechanisms proposed by other authors for the chemistry of these molecules in interstellar clouds. A large rate coefficient has been measured for the endothermic charge-transfer reaction between S⁺ and H₂S, and this is thought to indicate that significant amount of excited S⁺ are present in the afterglow when S⁺ formed by the reaction of He⁺ with sulphur-containing molecules.