We have studied the effects of oxygen atoms on the vibrational relaxation of shock-heated N2 over the temperature range from 1200 to 3000 °K, using the CO tracer technique. The measured relaxation times pτN2–O vary from 0.8 to 2 atm · μsec in this range with an uncertainty of ± 50%, in excellent agreement with existing high-temperature shock tube and low-temperature flow tube results. The weak temperature dependence of all these results is in marked contrast to theoretical predictions. Some limited measurements of the relaxation of CO by oxygen atoms yield values of pτCO–O of approximately 0.04 atm · μsec, in good agreement with other recent measurements. This rate is approximately 25 times as fast as the N2–O rate and, coincidentally, is approximately the same as that for the relaxation of O2 by O atoms. The greater rapidity of the CO–O and O2–O relaxation, compared with that of N2–O, may be the result of atom-exchange processes in the former cases.

Strong microwave absorption was observed when a 10 GHz source illuminated an underdense collisional plasma that had a density gradient scale length several wavelengths long. Significant reductions in angular scattering and cross-polarized components were also observed. These experiments confirm that absorption was the dominant process. The plasma was created by the photoionization of tetrakisdimethylaminoethylene molecules seeded into atmospheric pressure helium. Sparkboard arrays provided the intense vacuum ultraviolet ionizing radiation. Plasma density profiles were measured using transverse scans of 9.7 GHz probe microwaves and were found to approximate an Epstein profile. The absorption at 10 GHz by this plasma was as large as 28 dB in direct backscattering and 15–20 dB when orthogonally polarized microwaves were launched and detected. The peak absorption scales with sparkboard energy in a way that suggests that electron-ion recombination is the dominant electron-loss mechanism at high plasma densities.

The performance of Xe*2 as a 172-nm fluorescence or laser source when pumped by a low-current, long-pulse electron beam was determined. The fluorescence efficiency of Xe*2 is near the theoretical limit of ∼50% at modest pressures over a range of pump rates up to 106 W/cm. The laser efficiency is limited to values <1% by a very strong medium absorption that is probably due to Xe*2 photoionization. Laser performance is further degraded by early pulse termination that appears related to mirror degradation. An improved kinetics and extraction code was developed to model the performance of the Xe*2 system. A key component of the model is a more detailed treatment of the interactions between secondary electrons and excited atomic and molecular xenon states. Rates for these processes were derived as described herein. With this model, good absolute agreement was obtained between experiments and calculated parameters at pressures as low as 0.5 atm.