I. R. Gatland

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...

Tests of alkali ion-inert gas interaction potentials by gaseous ion mobility experiments

Gaseous ion mobilities are mainly dependent on ion–neutral collision energies in the range 0.03–1 eV and, using a recently developed kinetic theory method, can be directly related to ion–neutral interaction potentials. In this paper, experimental mobilities are used to test recent theoretical calculations based on the electron–gas model of the interaction potentials for the twelve combinations of Li+, Na+, K+, and Rb+ with He, Ne, and Ar. The model potentials are quite good, but some systematic discrepancies with experimental mobilities exist. These discrepancies are analyzed in terms of the relation between the mobility and the ion–atom potential.

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, diffusion, and clustering of K+ ions in gases

We have measured, with a drift tube mass spectrometer, the mobilities and longitudinal diffusion coefficients of K+ ions in nitrogen and carbon monoxide at 300°K. The measurements were made over a range of E/N extending from thermal values up to 636 × 10−17 V·cm2. Here E is the drift field intensity and N is the gas number density. The zero‐field reduced mobilities of K+ ions in N2 and CO were determined to be (2.54 ± 0.05) and (2.30 ± 0.04) cm2/V · sec, respectively. The low‐field diffusion coefficients are in excellent agreement with the values calculated by the Einstein equation from the experimental zero‐field mobilities. The experimental diffusion coefficients are compared with the predictions of an equation developed by Wannier on the assumption that the ion‐molecule interaction consists of only the attractive polarization force, of which a constant mean free time between collisions is a consequence. Comparison is also made with a modified version of this equation which contains the ionic drift velo...

Mobilities and longitudinal diffusion coefficients of K+ ions in argon gas

We have used a drift tube mass spectrometer to measure the mobilities and longitudinal diffusion coefficients of mass‐identified K+ ions in argon at 300°K. The range of E / N extended from 1 to 610 × 10−17V · cm2, where E is the electric drift field intensity and N is the number density of the neutral gas. The zero‐field reduced mobility of K+ ions in argon was found to be 2.66 ± 0.05 cm2/V · sec, in close agreement with the value previously reported by Tyndall for ions in argon that were assumed to be K+ but not mass identified. The low‐field diffusion coefficients agree well with the value predicted from the Einstein equation using the experimental zero‐field mobility. Our diffusion data are compared with theoretical predictions of Wannier and of Whealton and Mason, and with experimental data obtained by Skullerud using a drift tube lacking a mass spectrometer.

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.

Ion mobility test of Li+–Ar potentials

Theoretical potentials for the interaction of lithium ions with argon atoms have been developed by Kim and Gordon, and by Gordon and Waldman, using electron gas–Drude model calculations and by Olson and Liu using both SCF and CI calculations. In this paper the ion mobilities are obtained for each of these potentials and are compared with experimental data. The CI potential gives the best agreement with experiment but still differs significantly in the low E/N region. A potential which is directly determined to fit the experimental data only departs from the CI potential for internucleus separation distances larger than 6 a.u. and leaves the potential well (around 4.5 a.u.) almost unchanged.

Measurement of the rate coefficient of the reactions H+ + 2H2 → H3+ + H2 and D+ + 2D2 → D3+ + D2 in a drift tube mass spectrometer

The rate coefficient of the reaction H+ + 2H2 → H3+ + H2 has been measured at a gas temperature of 300 °K and over a pressure range 0.25–0.50 torr. The transport properties and average energy of a given species of ion drifting in a gas in a uniform electric field are determined by E/N, where E is the electric field intensity and N is the gas number density. E/N is expressed in units of the townsend (Td), where 1 Td = 10−17 V · cm2. Our measurements were made over a range 25–50 Td, where the lower value corresponds to an average energy for the reacting H+ ions which is very close to the thermal energy of the H2 molecules at 300 °K. No systematic variation of the rate coefficient was observed over the range of E/N which was covered. The measurements were made with a drift tube mass spectrometer and involved the detailed analysis of the arrival time spectra of the product H3+ ion. The rate coefficient was evaluated to be (3.05 ± 0.15) × 10−29 cm6/sec. The same result was also obtained for the reaction D+ + 2...

Mobility and diffusion of protons and deuterons in helium-a runaway effect

The mobility and diffusion of H+ and D+ ions in He gas are calculated classically, based on an accurate ab initio interaction potential. Comparison with corresponding quantal calculations of the zero-field mobility of H+ in He as a function of temperature shows that quantum effects are negligible above 50K, and are only 3% at 10K. Calculations as a function of electric field strength at fixed gas temperature indicate a runaway effect, in which the ions cannot lose enough momentum by collisions to achieve a steady-state average velocity. The drift-tube measurements of Howorka et al. (1979) are consistent with this interpretation.

Longitudinal diffusion of K+ ions in He, Ne, Ar, H2, NO, O2, CO2, N2, and CO

Longitudinal diffusion coefficients, measured with a drift tube mass spectrometer, are reported for potassium ions in helium, neon, hydrogen, nitric oxide, oxygen, and carbon dioxide for E/N in the range 1−700 Td (E is the electric field strength, N the neutral gas number density, and 1 Td = 10−17 V⋅cm2). These results, together with those previously reported for potassium ions in argon, nitrogen, and carbon monoxide, are compared with the theories of Wannier and of Mason, Whealton, and Viehland, which relate mobilities and diffusion coefficients.