Electron-ion recombination measurements in a flowing afterglow plasma.

摘要

The dissociative recombination of molecular ions with electrons involves the capture of a slow electron by an ion to form an intermediate complex which subsequently dissociates into neutral products. The objective of this work was to measure the recombination coefficients for several ions of interest in planetary ionospheres and in the interstellar medium, to identify some of the neutral products and to measure absolute yields for specific products.; The measurements were performed in a Flowing Afterglow Langmuir Probe-Laser Induced Fluorescence (FALP-LIF) apparatus, which consists of a plasma flow tube with Langmuir probe, mass spectrometer, emission spectroscopy and Laser Induced Fluorescence (LIF) diagnostics. The initial period of work involved building of and extensive testing of the apparatus. The first set of experiments involved measurements of the recombination coefficient for several ions. A novel method of data analysis was employed, and although we were able to confirm previous observations of Adams and Smith that the electron density decay of {dollar}rm Hsb3sp+/Dsb3sp+{dollar} plasmas does not obey the simple recombination law, we found no evidence for persistence of vibrational excitation in the ions invoked by these authors to explain their experimental observations. Instead, we proposed that a three-body process, and not dissociative recombination, was responsible for the experimental observations. For other ions our measurements were in good agreement with previous results, and we found no other examples of "abnormal" recombination.; Spatially resolved emission spectroscopy was used for the identification of electronically excited products for several ions. A recombination-dominated afterglow is a rather complicated system, and for that reason spatially resolved LIF measurements in conjunction with computer modeling of the afterglow were used for measuring absolute yields for the production of ground state OH in v = 0,1 by the dissociative recombination of {dollar}rm Hsb3Osp+, HCOsb2sp+, HNsb2Osp+,{dollar} and HCO{dollar}sp+{dollar} ions. The OH(v = 0) yields were in good agreement with a previous measurement of Herd and Adams while for OH(v = 1) we found serious discrepancies which we attributed to the contribution of extraneous reaction not accounted for in the experiment of the above mentioned authors.