Techniques of microwave-pulse flash-spectroscopy

Abstract

Various designs were investigated for the production of homogeneous discharge in gases, with single pulses of microwave radiation. The objective was to produce discharge in long columns of gas (∼1 m) for electronic absorption spectroscopy, at moderately high pressures of ∼1/3 atm, without causing any significant change of gas temperature. A pulser was constructed to operate the English Electric magnetrons M561 and M578 on single shot to cover the range 20-800 kW and 0.5-10 µs. One suitable design was realized. A quartz reaction vessel, 5 mm diam. and 0.5 m long, was located centrally inside waveguide 10. The experimental gas was subject to a single traversal of a microwave pulse, most of the energy of which was absorbed in a terminating matched load. Thereby an unattenuated discharge could be produced with up to at least 300 Torr of He. Application of the method is illustrated with the formation and relaxation of C₂X³Π_u in CO + He mixtures, the relaxation of NO X²Π(ν= 1, 2, 3) in pulsed NO + He, and relaxation of He₂a³∑⁺_u in pure He.

A second possible design was suggested in which discharge would occur simultaneously in 8 cylindrical cavities, each 10 cm long. The method was successfully operated with 2 cavities. Full details of the designs are given.