Field ionization of C2H5I in supercritical argon near the critical point

Field ionization of C2H5I doped into argon is presented as a function of argon number density along the argon critical isotherm. These data exhibit a decrease in the argon-induced shift of the C2H5I ionization energy near the critical point similar to that observed in recent field ionization measurements of CH3I/Ar. We show that this decrease is due to the interaction between argon and the quasi-free electron arising from dopant field ionization and is, therefore, independent of the dopant. The energy of the quasi-free electron is calculated in a local Wigner-Seitz model containing no adjustable parameters to within ±0.2% of experiment. (letter to the editor)