Kinetic studies of group VI metastable atoms and molecules

• Main Author: McElroy, William John
• Published: University of Edinburgh 1979
• Subjects: 541.39
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.666189

Kinetic processes involving the low-lying metastable electronically excited states of the group VI atoms, oxygen and sulphur, and diatomics, 02, S2 and SO have been investigated. Singlet molecular oxygen, 02(1Ag) was generated by the reaction of hydrogen peroxide with sodium hypochlorite and its subsequent decay monitored by the 'dimol' emission at A = 633 run. A simple experimental arrangement is described for determining the rate constants for quenching of 02(1Ag) by 02(3? g) and H20. it was shown that conditions were readily obtainable under which the decay of 02(1Ag) in the bubbles was controlled by quenching in the gas phase, and where gas-surface interactions were negligible. Singlet sulphur monoxide, SO( 1A), was produced by the reaction of 0(21 D2) atoms with OCS. The initially rapid removal of ozone in this system was accounted for by the reaction of S0(IA) with 03. Rate constants for the reactions of both SO(1A) and S0(3? ) with 03 were obtained by computer modelling. Photolysis of OCS (A > 200 nm) yields S(31D2) atoms, which react on almost every collision with carbonyl sulphide to produce singlet molecular sulphur, S2(1Ag). Both S2(1Ag) and S2(3?g ) were observed in absorption using kinetic spectroscopy. A rate constant for quenching of S2(lAg) by OCS was obtained from the formation kinetics of ground state sulphur, S2(3?g ). This process is discussed qualitatively in terms of electronic to vibrational energy transfer. Photolysis of 03,(Au.v. < 310 nm) was employed as a source of O(21D2)atoms. The primary and secondary reactions which follow ozone photolysis were investigated. Ozone was monitored by kinetic absorption spectrophotometry at A = 253.7 mm. Computer modelling studies were carried out and these provided a better understanding of the processes involved, and in particular, with regard to the reaction of 0(21D2) atoms with ozone. The reactions of 0(21 D2) atoms with several chlorofluoromethanes in the presence of ozone were studied. Schemes are presented to account for the observed removal of ozone obtained for CF3C1 and CF 2C12.