Laser flash photolysis studies of some oxygen(D[1,2]) and OH(X(2)Pi) reactions of atmospheric interest.

摘要

A major focus of the research described in this dissertation is investigation of the gas phase atmospheric chemistry of hydrogen cyanide, HCN. The atmospheric chemistry of HCN was studied by investigating its reactions with the ground state OH radical, OH(X2Π), and with the electronically excited oxygen atom, O(1D₂). In addition, a number of other O(1D₂) reactions of atmospheric importance have also been studied.; A laser flash photolysis-laser induced fluorescence (LFP-LIF) technique was employed to study the kinetics and mechanism of the reaction of OH with HCN (RI) as a function of temperature and pressure over the ranges 268–371 K and 10–600 Torr, respectively. The LFP-LIF experiments involved time-resolved detection of OH by pulsed laser-induced fluorescence spectroscopy following laser flash photolysis of H₂O₂/HCN/N₂, H ₂O₂/HCN/O₂/N₂, and H₂O ₂/HCN/O₂ mixtures. The rate coefficient for R1 is found to be considerably slower than previously thought, a result that is consistent with the observed independence of the stratospheric HCN mixing ratio on altitude. The rate coefficient for R1 increases with increasing temperature and with increasing pressure. The values for the room temperature low pressure limiting rate coefficient (k₀) and the high pressure limiting rate coefficient (k_∞) are estimated to be 4.0 × 10−33 cm6molecule−2s−1 and 9.5 × 10−15 cm3 molecule −1s−1, respectively. The observed pressure dependence of R1 is typical of an addition reaction, while the observed temperature dependence suggests that addition is not a barrierless process.