HIGH RYDBERG STATES OF METHYL-IODIDE PERTURBED BY NITROGEN - A MUTUAL CANCELLATION OF SHIFT TERMS

The dependence of the positions of both prethreshold and autoionizing high Rydberg states of CH3I on the density rho of the perturber N2 was measured at room temperature, using synchrotron radiation. Up to rho = 2.2 x 10(20) cm-3 no pressure shift was observed, showing that the scattering shift by the valence electron is compensated by the polarization shift due to the core. From the results, the value A = (1.9 +/- 0.3) x 10(-9) cm was found for the scattering length, in good accord with previous pressure shift and swarm results. The wide range of useful applications of the photocurrent excitation spectra to the study of perturbed transitions is stressed.