Absolute Collisional Excitation Cross Section Measurements Using Crossed Molecular Beams

Andrew Freedman

Jan 1983 · Air Force Geophysics Laboratory, Air Force Systems Command, United States Air Force

About this ebook

The measurement of absolute excitation cross-sections of the asymmetric stretch mode (001) of H20 and C02 for collisions with atomic oxygen is important in understanding the signatures of high-altitude rocket plumes. Experiments are performed in a crossed molecular beam apparatus in which a CVF detector measures the collisionally-induced infrared fluorescent signal. Calibration and testing of the atomic oxygen source was completed. It was installed into the crossed beam apparatus and vacuum tested in preparation for performing the excitation cross-section measurements. Upper limits have been established for the excitation cross sections for the systems 0 + C02 and Ar + C02. The values determined are 0.03A squared for 0 + C02 at 3.85 km/sec and 0.003 A squared for Ar + C02 at 2.27 km/sec. Monte Carlo trajectory analysis of the data provides accurate correction factors to the raw data that account for kinematic and experimental constraints inherent in these measurements. It further shows that measurements near threshold cannot be used to determine the functional energy dependence of the cross section. Further modifications and improvements in the experimental approaches to improve sensitivity will be discussed.