Measurements and analyses have been made of electron impact ionization and of current growth in pulsed, low-current, prebreakdown discharges in parallel-plane geometry in N2 at very high electric field to gas density ratios E/n and low products of the gas density n and electrode separation d. The E/n range and nd ranges were 1<E/n<52 kTd, where 1 Td=10−21 V m2 , and 6×1018 <nd<3×1020 m−2 (or 0.02<pd<1 Torr cm, where p is pressure) and were below breakdown values. Measurements were made of the transported charge on the time scales of electron transit, ion transit, and metastable decay. Measurements were also made of the growth of steady-state discharge currents as a function of discharge voltage. The contributions of avalanches resulting from ion- and metastable-induced secondary electrons were determined from the ratio of electron-excited N+2 391.4-nm emission integrated over all avalanches to the integrated emission during the laser-initiated electron pulse. Calculations based on ionization by electrons only show good agreement with the measured charge transported during the electron avalanche and with the current multiplication. Analysis of 391.4-nm emission data and of charge transported at E/n≥10 kTd and voltages near breakdown using the assumption of electron impact ionization leads to large apparent secondary electron yields at the cathode which increase significantly with nd. At E/n≥10 kTd, and for the voltages of our experiments, fast N2 produced in charge transfer collisions of N+2 with N2 appears to provide most of the secondary electrons. The apparently small contribution of ionization of N2 by N2, N+2 , N, and N+ is consistent with our assumption that each of these ionization cross sections is equal to that for N2-N2 collisions and so are much smaller than for Ar+ -Ar or Ar-Ar collisions.

A spontaneous Raman imaging system (SRIS) has been developed that can monitor chemical oxygen-iodine laser (COIL) singlet oxygen generator (SOG) performance in real time. This system permits one to monitor directly the SOG performance by measuring O(2)(a(1)D) and O(2)(X(3)?) simultaneously with a single intensified CCD array at the exit of an imaging monochromator. We present the results from tests conducted on a 0.25-mol SOG using a prototype Raman system. Performance and validation of a highly sensitive SRIS that was designed and built specifically for SOG diagnostics are discussed. Detection and possible interferences of other species relevant to COIL devices such as I(2) and Cl(2) are investigated.

This work reports the measurements of rate coefficients for excitation transfer reactions of metastable He(2 3S) atoms, produced in 0.3–4 atm of helium, with various reactants presenting a wide range of characteristics. In all cases studied, three-body reaction channels were identified with most probable values of rate coefficients lying in the range from 0.2 to 6.7×10−31 cm6 s−1, for Ne and N2O, respectively. These are generally more than one order of magnitude smaller than previously reported. The interpretation of this discrepancy in terms of a more reactive intermediate He2(Σ*) complex in dynamic equilibrium with the He(2 3S) population seems to be confirmed, and is analyzed in some detail.

Electronically excited iodine atoms [I(*)((2)P(1/2))] are created when ICI is injected into a stream of chemically produced NCl(a(1)Delta). Using an optical double-resonance technique, we observed a population inversion between the 5(2)P(1/2) and 5(2)P(3/2) states of atomic iodine.