ELECTRIC-FIELD IONIZATION OF HIGH RYDBERG STATES AND VERTICAL IONIZATION-POTENTIAL OF AN IMPURITY IN DENSE FLUID ARGON

We present experimental results of field ionization of high Rydberg st ates of an impurity doped into a dense medium. The experiments allowed us to determine the change of the vertical ionization potential of CH 3I in fluid argon up to the critical density. The lowering of the vert ical ionization potential as a function of the argon number density (r ho) is explained quantitatively on the basis of the energy of the lowe st extended state of an excess electron (V0) in argon and on the sudde n polarization energy resulting from the interaction between the dopan t ion and the medium. Our results for V0(rho) are compared with severa l recent theoretical calculations.