The Hydrogen Molecular Ion: The Simplest, but the Most Fundamental System for Understanding Chemical Bonds

Abstract

The simplest molecule among all is the hydrogen molecular ion H. The ion can be obtained by ionizing H₂ molecules through electron bombardment, for example. In the presence of neutral H₂ molecules, the ion is subjected to a fast chemical reaction, H ⁺₂ + H₂ → H ⁺₃ + H. If this reaction is suspended by some means, the thermodynamically stable H₂ ion can be observed spectroscopically. Through such observation, the ion is found to be stable by as much as 269 kJ mol⁻¹ = 2.79 eV, relative to the dissociation limit of H + H⁺.