H. W. Ellis

Ion identity and transport properties in CO2 over a wide pressure range

We have investigated in drift tube mass spectrometers the identity and the transport properties of ions formed in CO2 gas at pressures ranging from 10−4 to 762 torr. Under bombardment by low energy (20–100 eV) electrons in the ion source, the primary positive ion is predominantly CO+2, with traces of C+, O+, and CO+. The predominant ion becomes O+2 at pressures above 100 μ (0.1 torr), and clustering of CO2 molecules to the O2+ occurs even at pressures below 1 torr. Break‐up of the clusters also occurs, the ion identity changing many times in the drift region. The zero‐field reduced mobility of the O+2⋅ (CO2)n charge carrier is a function of pressure, and varies from (1.30±0.03) cm2/V⋅sec at 0.2 torr to (1.18±0.03) cm2/V⋅sec at 1 torr. The sole negative ion produced directly by the electron bombardment is O−, which clusters to form the stable ion CO−3, whose reduced mobility is (1.27±0.06) cm2/V⋅sec for E/N ?60 Td at all pressures below 1 torr. At much higher pressures and under somewhat different conditio...

The Li+–He interaction potential

New measurements of the mobility of Li+ ions in He gas at 300°K are reported for a wide range of E/N, the ratio of the electric field strength to the gas number density. These data are used in conjunction with kinetic theory to test various Li+–He interaction potentials over a wide range of separation distance. It is shown that the ab initio potential of Hariharan and Staemmler gives mobility values in excellent agreement with experiment at low and moderate E/N, but that significant discrepancies exist at high E/N. The mobility data are also directly inverted to give the Li+–He interaction potential. This directly determined potential is in excellent agreement with the ab initio at intermediate and long range, but differs significantly in the short‐range region. In the latter region, however, it is in agreement with the potential obtained by analysis of beam‐scattering experiments.

Mobility of Cl− ions in Xe gas and the Cl−–Xe interaction potential

The mobility of Cl− ions in Xe gas at 300 °K has been measured in a drift tube mass spectrometer for a wide range of values of the ionic energy parameter E/N (the ratio of the electric field strength to the neutral gas number density). A Cl−–Xe interaction potential is assumed and a kinetic theory appropriate for the ion motion is used to derive the mobility from the potential. Then an iterative technique is used to modify the potential so as to fit the predicted mobility to the experimental data. This interaction potential is directly determined by the experimental data for a range of internuclear separation distances from about 4 to about 10 a.u. At distances greater than 10 a.u., the potential is the induced dipole polarization potential.

Longitudinal diffusion coefficients of Li+ and Na+ ions in He, Ne, and Ar: Experimental test of the generalized Einstein relation

We have measured, with a drift tube mass spectrometer, the longitudinal diffusion coefficients of Li+ and Na+ ions in He, Ne, and Ar at a gas temperature of 300 °K. The measurements were made as a function of the energy parameter E/N, where E is the electrostatic drift field strength and N is the gas number density in the drift tube. The range of the steady‐state, average ionic energy thereby covered extended from close to the thermal value up to 10.1 eV in the case of Li+ in He and a few eV less in the other ion–atom combinations. The experimental data are compared with the results of computations based on three different equations: the original Wannier equation derived for the polarization attraction model, our modification of this equation, and the generalized Einstein relation discussed in the paper immediately preceding this paper [Larry A. Viehland and E. A. Mason, J. Chem. Phys. 63, 2913 (1975)]. The latter relation is superior to the other two in the present application and gives excellent agreeme...

Test of the Li+–He interaction potential

The mobility of Li+ ions in He has been measured at a gas temperature of 300 °K over a wide range of E/N, where E is the electric field intensity and N is the gas number density. A new theory of ion mobility is used to calculate from these data the standard Ω integral ?(1,1) of kinetic theory for Li+ in He over a range of effective gas temperature extending from 300 to 28 700 °K. The ab initio quantum mechanical interaction potential for the Li+–He system computed by Catlow et al. is also used to calculate ?(1,1) as a function of Teff. A comparison of the two sets of data serves as a test of the Catlow potential. The test is extended to still higher effective temperatures (up to 60 000 °K) by comparison with values of ?(1,1) computed from the short‐range repulsive potential derived from Li+ beam scattering experiments in helium. The Catlow potential reproduces the general features of the dependence of the ’’experimental’’ Ω integral on Teff over the entire range of the test. However, significant discrepan...

Mobility of Cl− ions in Ne, Ar, and Kra)

Using the Georgia Tech drift tube spectrometer, measurements were made at 300°K of the mobilities of 35Cl− in Ne, Ar, and Kr as a function of electric field and gas number density. (AIP)

Mobilities and longitudinal diffusion coefficients for Cs+ ions in He and Ne gas

Ion mobilities and longitudinal diffusion coefficients of Cs+ are measured in He and Ne gas using the drift tube mass spectrometer.(AIP)

Longitudinal diffusion coefficients and the generalized Einstein relation for Cl− ions in Ne, Ar, Kr, and Xe

Longitudinal diffusion coefficients have been measured for Cl− ions drifting in Ne, Ar, Kr and Xe gases under the influence of a uniform constant electric field. The measurements were made at gas temperature 300 °K and pressure below o.5 Torr. (AIP)

Temperature dependent mobilities: O2+ and NO+ in N2

The zero field mobilities of O2+ and NO+ in N are reported over a temperature range of 305°‐640°K. The measurements were performed in the pressure range 30–42 Torr. (AIP)