1 Photoionization studies of C 2 H 5 I and C 6 H 6 perturbed by Ar and SF

We present photoionization spectra of C2H5I and C6H6 doped into Ar and SF6, and photoabsorption spectra of C2H5I doped into Ar. The observation of subthreshold photoionization in C2H5I/SF6 and C6H6/SF6 is discussed in terms of dopant (D)/perturber (P) interactions involving the excited state processes of D + P 6 D + P and D + P 6 [DP] + e, where D is a discrete Rydberg state of the dopant. The density-dependent energy shifts of high-n Rydberg states observed in the subthreshold photoionization spectra are used to obtain the zero-kinetic-energy electron scattering length for SF6. Similarly, the zero-kinetic-energy electron scattering length of Ar obtained from the density-dependent energy shifts of C2H5I Rydberg states is presented. (Electron scattering lengths obtained here for SF6 and Ar accord with values previously obtained using the density-dependent energy shifts of high-n Rydberg states of CH3I doped into these two perturber gases.)