Knowledge Bank

The methoxy radical is produced in the troposphere as a chemical intermediate in the breakdown of methane by the hydroxyl radical. It reacts with molecular oxygen to form formaldehyde as a stable product. Various buffer gases, namely helium, argon and nitrogen, were used as carriers to transport the methylnitrite precursor to the photolysis zone. Following excimer laser-induced photodissociation of the precursor, the methoxy radical was excited with a frequency-doubled Nd: YAG-pumped dye laser. Laser-induced fluorescence (LIF) signals were closely monitored under different conditions of temperature $(22-150\circ C)$ and oxygen pressures (0-40 torr). Temporal histories of the methoxy fluorescence decay were obtained by recording the LIF signal intensity as a function of increasing time delay between the photolysis and probe laser pulses. Stern-Volmer plots of the inverse first-order decay constant $(\tau 1)$ versus oxygen pressure at different temperatures allowed determination of the rate constants for the reaction of methoxy with oxygen and the derivation of an appropriate Arrhenius expression over the temperature range $22-150\circ$C. Helium as buffer gas was able to quench the fluorescence from the methoxy radical more rapidly then either nitrogen or argon.