Kinetic investigations of selected alkaline-earth atoms by time-resolved spectroscopic methods including laser-induced atomic fluorescence and molecular chemiluminescence

• Main Author: Adams, J. W.
• Published: University of Cambridge 1996
• Subjects: 543.5
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.595351

This thesis is concerned with the kinetic investigation of gaseous alkaline-earth atoms in specific electronic states by time-resolved spectroscopic methods. The first part of the thesis is directed towards a study of the collisional behaviour of ground state atoms, in particular, Sr[5s<SUP>2</SUP>(<SUP>1</SUP>S<SUB>0</SUB>)], generated by pulsed irradiation and monitored by time-resolved atomic resonance absorption spectroscopy. In broader terms, it was also envisaged that this would provide a framework for considering and comparing the behaviour of this atom in both ground and excited state reactions, especially that of Sr[5s5p(<SUP>3</SUP>P<SUB>J</SUB>)], described later in the thesis, in order to investigate the relationship between collisional behaviour and electronic structure. Whilst this method did not yield data for Sr[5s<SUP>2</SUP>(<SUP>1</SUP>S<SUB>0</SUB>)], the investigation did provide a structure for considering alkaline-earth atom chemistry in general. The second part of the thesis describes the study of the collisional behaviour of the electronically excited strontium atom, Sr[5s5p(<SUP>3</SUP>P<SUB>J</SUB>)], generated by pulsed laser excitation at elevated temperatures. The reactions of this optically metastable atomic state with the molecules CH<SUB>3</SUB>Cl, CF<SUB>3</SUB>Cl, CH<SUB>3</SUB>Br and CF<SUB>3</SUB>Br were studied by both time-resolved atomic emission from Sr[5s5p(<SUP>3</SUP>P<SUB>1</SUB>)] → Sr[5s<SUP>2</SUP>(<SUP>1</SUP>S<SUB>0</SUB>)] and time-resolved molecular chemiluminescence from SrX(A<SUP>2</SUP>Π<SUB>1/2,3/2,</SUB> B<SUP>2</SUP>Σ<SUP>+</SUP> - X<SUP>2</SUP>Σ<SUP>+</SUP>), following halogen atom (X = Cl, Br) abstraction. Quantitative characterisation of the time-dependencies of the atomic and molecular emissions indicated direct halogen abstraction by Sr(5<SUP>3</SUP>P<SUB>J</SUB>). Branching ratios into these specific molecular electronic states were derived by computerised integration of the intensities of the atomic and molecular decay profiles and were shown to be statistical in nature.