ABSOLUTE FLUORESCENCE CROSS-SECTIONS AND QUANTUM YIELDS IN $NO_{2}$

Abstract

In this work we have measured fluorescence cross-section and quantum yields in the laser induced fluorescence of $NO_{2}$. A low pressure sample of $NO_{2}$ (typically 5 to 50 $\mu$) was excited by either the second harmonic of a Nd: YAG laser (532.1 nm. 0.35 nm bandwidth) or a dye laser operating in the 430-450 nm range (approx. .003 nm bandwidth). Fluorescence was observed spectrally resolved by a monochromator and time resolved by a boxcar integrator. Time resolution allowed measurement from collision-free through collisional-quenching regimes. Relatives calibration of the detection system was performed using a standard lamp Raman scattering from $N_{2}$ and $O_{2}$ served as absolute intensity standards so that absolute cross-sections for scattering into a fixed fluorescence band width were obtained in both the collision-free and collision-dominated regimes. Absolute fluorescence cross-sections have thus been measured into the 000 through 002 vibrational band of the fluorescence spectrum. Quantum yields into fixed fluorescence band-widths have been determined from these data and measured absorption cross-sections. In addition the time evolution of the fluorescence and dependence upon self-quenching and quenching in $N_{2}$ and $O_{2}$ have been explored.