Spectral shift of autoionizing high-n Rydberg states of $\mathrm{CH_3 I}$ in dense argon: a photoionization study

Photoionization spectra of pure CH3I and of CH3I doped into varying densities of Ar (up to 10.5 × 1020 cm−3 are reported. The photoionization spectrum of pure CH3I closely reproduces the absorption spectrum of the autoionizing nd′ and ns′ Rydberg states converging to the 2E12 ionization limit. Moreoever, it displays the members of the nd′ series terminating on the v′ = 1 vibrational level of the same limit. The Rydberg states shift to lower energies with increasing argon density. The shift rate for principal quantum number n > 10 is in good agreement with the values obtained from absorption studies