Electron mobilities have been measured in low density helium and nitrogen gases as reference standards in the ongoing study of effects of molecular shape and density on electron transport in fluids. Wider temperature ranges were used than heretofore. Electron mobilities in helium gas at temperatures T=11–466 K and densities n=4.9–7.3 (1025 molec/m3) are consistent with previously reported scattering cross sections. The value of σm at 10−23 J (10−4 eV) is 4.9×10−20 m2, corresponding to a scattering length of 6.2×10−11 m. Density normalized mobilities nμ in nitrogen gas at T=66–460 K and n=0.9–6.7 (1025 molec/m3) decrease with increasing density. Values of nμ extrapolated to low field strengths and zero density gave values which were used to estimate momentum transfer cross sections. Further study of electron scattering by nitrogen at energies <3×10−21 J (20 meV) is desired.

Ionizing radiation passing through a fluid produces an ion–electron pair by knocking an electron off a molecule. The electron possesses excess energy, which it loses in collisions with molecules as it moves away from the ion. These are stochastic processes. The distance travelled during thermalization determines the probability that the electron ultimately escapes the Coulombic field of the ion to form freely diffusing ions. Free-ion yields were measured in X-irradiated sulfur hexafluoride at 5.7 ≤ d(kg m−3) ≤ 1860, corresponding to the vapor and liquid at 202.8 ≤ T(K) ≤ 324.1. (The critical fluid has dc = 730 kg m−3 and Tc = 318.7 K). The electric field dependence of the yield was best fitted using an electron thermalization distance distribution function F(y) that was Gaussian with a power tail. The most probable thermalization distance bGP was estimated at each density. The density-normalized electron-thermalizing ability of the fluid decreased with increasing gas density and was independent of density in the liquid phase. The dependence is different from those observed in hydrocarbons and might reflect a density effect on the energy dependence of the electron-attachment reaction.

The free ion yield in x-irradiated liquid nitrogen at zero applied field strength increases from G0fl=0.0034 ion pairs/100 eV at 77.1 K to 0.043 at 123.7 K, while the density-normalized thermalization distance of the secondary electrons increases from bEPd=4.4×10−6 to 5.6×10−6 kg/m2. The ratio of the GEfi values at 123.7 and 77.1 K decreases from 13 at E=0 to 3.1 at E=5.2 MV/m. Yields calculated from the extended Onsager model agree with the measured values only when the electron thermalization distance distribution is assumed to be exponential with an added power tail (YEP): F(y)=YE, 0<(y−y0)<3.5bEP; F(y)=YE+0.74b2EP/(y−y0)3, (y−y0)>3.5bEP; where YE=b−1EP exp[(y0−y)/bEP], y>y0. The electron thermalization process in liquid nitrogen appears to be truncated by electron capture to form an anion.

Electron mobilities in low density helium and nitrogen gases: Momentum transfer cross sections at very low energies Quenching cross sections for electronic energy transfer reactions between metastable argon atoms and noble gases and small molecules

. Can. J. Chem. 66, 1304Chem. 66, (1988. Electron thermalization in X irradiated liquid CO is truncated by electron capture to form an anion, as it is in liquid N2. The thermalization distance distribution in these two liquids is a modified exponential, rather than the modified Gaussian obtained in liquid hydrocarbons where electron capture does not occur. The density normalized distance parameter bEpd in CO was constant, 2.8 x kg/m2, at densities 2.7 2 d/dc > 2.0, but increased somewhat at lower densities, reaching 3.3 X lop6 kg/m2 at d/dc = 1.4. The thermalization distances in CO are about two thirds those in N2 at the same density. Electrons are captured more readily by CO than by N2.G. RAMANAN et GORDON R. FREEMAN. Can. J. Chem. 66, 1304 (1988. Comme il a Ct C observC anterieurement dans le Nz liquide, la thermalisation des Clectrons dans le CO liquide irradiC par des rayons-X est tronquCe par une capture dYClectron qui forme un anion. Dans ces deux liquides, la distribution de la distance de thermalisation est une exponentielle modifiee plut6t que la distribution de Gauss modifiCe observke dans les hydrocarbures liquides dans lesquels la capture d'Clectron ne se produit pas. Dans le CO, a des densites 2,7 2 d/dc > 2,0, le paramktre de distance normalis6 pour la densitC, bEpd, est constant 1 2,8 X kg/m2; toutefois, 1 des densitCs plus faibles, cette valeur augmente pour atteindre 3,3 x lop6 kg/m2 a d/dc = 1,4. A la m&me densitC, la distance de thermalisation dans le CO est environ les deux tiers de celle dans le N2. I1 se produit une capture plus rapide des Clectrons dans le CO que dans le N2.[Traduit par la revue] Introduction The distribution of electron thermalization distances in X irradiated liquid nitrogen has been found to be non Gaussian (I), which is different from those in hydrocarbons (2). The distribution is mainly a one-dimensional exponential, attributed to truncation of the electron thermalization process by electron capture (3). Carbon monoxide is isoelectronic with nitrogen, and both form transient anions with low energy electrons, carbon monoxide at 0.27 aJ (1.7 eV) and nitrogen at 0.37 aJ (2.3 eV) (4). We therefore chose carbon monoxide for a comparative study.The rotational constants for CO and N2 are B = 3.9 x lopz3 J and 3.6 x lopz3 J, respectively, and the vibrational quanta are also similar, respectively 4.4 x lop2' and 4.3 x J (5). The electric moments are more different: dipole 3.7 X C m (6) and zero; quadrupole 6.0 X C m2 (7) and 5.1 x C m2 (8) for CO and N2, respectively. Thus rotational and vibrational excitation by low energy electrons are more efficient for CO (4b, 9) than for N2 (10) in the gas phase, and presumably also in the liquid phase. One might therefore expect shorter thermalization distances in liquid carbon monoxide than in liquid nitrogen at the same density. Experimental MaterialsMatheson Research Grade CO (99.99%) with sub ppm levels of oxygen, methane, ethane, and hydrogen, and other impurities like carbon dioxide (<5 pprn), nitrogen (-35 pprn), propane (-35 pp...