The interaction of ions with nonpolar neutrals: The collision broadening of ion cyclotron resonance lines of ions in hydrogen and methane

Abstract

The motion of ions in an ion cyclotron resonance cell is considered, and measurements of ion cyclotron resonance linewidths are described. The connection between cyclotron resonance linewidths and kinetic parameters is developed. Mobilities and collision frequencies of CH₅⁺, C₂H₅⁺, C₃H₇⁺, C₄H₉⁺, and Na⁺ in methane and H⁺, H₃⁺, H₃0⁺, CH₅⁺, C₂H₅⁺, C₃H₇⁺, and Na⁺ in hydrogen are determined from the linewidth measurements. Resulting mobilities of H⁺, H₃⁺, and Na⁺ in H₂ are found to agree well with drift tube measurements, in contrast to previous cyclotron resonance linewidth determinations. The mobilities are interpreted in terms of three model ion molecule interaction potentials. The mobilities are found to be in general consistent with both a three term 12–6–4 potential and an acentric potential but not with the simple polarization potential. Potential parameters consistent with binding energies from the literature and the present mobility measurements are reported for H₃⁺–H₂, CH₅⁺–CH₄, and C₂H₅⁺–CH₄.