Density effects on high-n molecular Rydberg states: CH3I in argon.

Abstract

Absorption spectra of the high-n molecular Rydberg states of ${\mathrm{CH}}_{3}$I, perturbed by varying number densities of argon (up to \ensuremath{\sim}11\ifmmode\times\else\texttimes\fi{}${10}^{20}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$), are reported. Red shifts, which increase with increasing argon number density, are observed for both discrete and autoionizing states. These red shifts vary linearly with the perturber number density for principal quantum numbers n\ensuremath{\ge}10. We explain these results quantitatively on the basis of the electron scattering length in argon, as well as the polarization of the medium by ${\mathrm{CH}}_{3}$${\mathrm{I}}^{+}$.