Laboratory studies of excited atom reactions
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
Recent interest in electronically excited atoms and molecules has stemmed from a desire to know more about some species found in the upper atmosphere. This thesis reviews studies of two excited atoms O(¹D) and H(²P). Attempts were made to study the reactions of O(¹D) with N₂O and CO₂. The difficulties encountered in this study are discussed. A method of distinguishing luminescence arising from primary reactions of a short lived excited species from other light emitted in the reaction system was used in the study of H(²P). In this method the ground state hydrogen atoms were excited by a Lyman-α lamp. The lamp was operated from the a.c. mains so that its output at 1216Å was modulated at 100 Hz. Consequently the population of the short-lived H(²P) was modulated at 100 Hz and any luminescence arising from allowed transit ions or electronically excited species produced by its reactions was therefore also modulated in phase with the lamp. This luminescence could be distinguished from scattered light from the lamp by its dependence on the simultaneous presence of both ground-state atomic hydrogen and the molecular reactant. Using this method in the following reaction mechanisms we detected: OH(²Σ) from H(²P) plus O², NH(³π) from H(²P) plus N₂, NO and N₂O, CH(²Σ) from H(²P) plus CO and CO₂, and SH(²Σ) from SO₂ plus H(²P). To determine whether there was a relation between the. chemiluminescent reactions and the overall reactions of H(²P), the Stern-Volmer equation was applied to quenchings, by each of the reactants, of 1216Å fluorescence in an atomic H gas. Difficulties encountered owing to trapping of 1216Å radiation in the atomic hydrogen vapour are discussed. From the quenching measurements rate constants and crosssections for the quenching of Lyman-α fluorescence by O₂, N₂, NO, N₂O, CO, CO₂, SO₂, H₂ and Ar were obtained.