Measurement of the rate constant for NO–O chemiluminescence using a calibrated piston source of light

A calibrated piston source of light, which provides a uniform disc of luminosity, has been used to study NO–O chemiluminesence produced in a cylindrical volume. The source was moved along the axis of the cylinder, with the luminous disc simulating cross-sectional layers of chemiluminescent gas. Direct comparison was thus made between the light collected from the calibrated source and from the volume of chemiluminescent gas, without the need for geometrical analysis of light paths. This comparison allowed the absolute photon output of the chemiluminescence to be measured as a function of wavelength. From these measurements the rate constant for the reaction NO+O→NO2+hν has been determined over the wavelength range between 0.54 and 1.27 μm.