Rate coefficients for excitation of the b 1Σ+g state of O2 by low energy electrons have been measured using a drift tube technique. The time dependence of the absolute intensity of the 762 nm band emission was measured for O2 densities between 1016 and 2×1018 molecules/cm3. When corrected for electron attachment, ionization, and metastable diffusion, the number of b 1Σ+g molecules produced per centimeter of electron drift and per O2 molecule calculated from the 762 nm emission varied from 1.3×10−18 cm2 at E/N=5×10−17V cm2 to 2.1×10−16 cm2 at E/N=2×10−15V cm2. These values of electric field to oxygen density ratio E/N correspond to mean electron energies of 0.75 and 6 eV, respectively. Measured decay constants for the 762 nm radiation yield a value for the product of the diffusion coefficient and the O2 density of (5.0±0.3) ×108 cm−1 sec−1 and a quenching coefficient for the b 1Σ+g state of (3.9±0.2) ×10−17 cm3 sec−1. Comparison of measured excitation coefficients with values calculated using a recommended set of electron collision cross sections for O2 show that the cross sections for direct excitation of the b 1Σ+g state are accurate near threshold and suggest that essentially all of the O2 molecules excited to levels at and above 1.63 eV result in the formation of molecules in the b 1Σ+g state.

The electron ionization coefficients for Ar, Kr, and Xe have been measured in the low E/N region [(0.5–4) ×10−16 V cm2] using a drift-tube apparatus. At low field values, the ionization coefficient was found to be anomalously large, a fact attributed to surface photoelectron emission from radiating metastables. This contribution also explains the discrepancy between earlier measurements and recent calculations based on the transport equation. The measurements were analyzed on the basis of two contributions to the ionization rate and calculations of the transport equation, yielding a revised set of inelastic cross sections which differ from earlier ones primarily in the inclusion of shape resonances.

Two techniques are described for synthesizing nanometer-sized TiB 2 particles by gas-phase combustion reactions of sodium vapor with TiCl 4 and BCl 3 : a low-pressure, low-temperature burner and a high-temperature flow reactor. Both methods produce TiB 2 particles that are less than 15 nm in diameter. The combustion by-product, NaCl, is efficiently removed from the TiB 2 by water washing or vacuum sublimation. Material collected from the low-temperature burner and annealed at 1000 ± C consists of loosely agglomerated particles 20 to 100 nm in size. Washed material from the high-temperature flow reactor consists of necked agglomerates of 3 to 15 nm particles. A thermodynamic analysis of the Ti͞B͞Cl͞Na system indicates that near 100% yields of TiB 2 are possible with appropriate reactant concentrations, pressures, and temperatures.TiCl 4 1 2BCl 3 1 10Na°! TiB 2 1 10NaCl . (1) Calcote and Felder 9,10 have recently proposed producing metals and nonoxide ceramics from reactions of 948