Photoionization spectra of CH3I and C2H5I perturbed by CF4 and c-C4F8: electron scattering in halocarbon gases

Photoionization spectra of CH3I and C2H5I doped into perturber halocarbon g ases CF4 (up to a perturber number density of 6.1x10(20) cm(-3)) and c-C4F8 (up to a perturber number density of 2.42x10(19) cm(-3)) disclosed a redsh ift of the dopant autoionizing features that depends linearly on the pertur ber number density. In the case of CF4, which is transparent in the spectra l region of interest, this redshift was verified from the dopant photoabsor ption features as well. From the perturber-induced energy shifts of the dop ant Rydberg states and ionization energies, the zero-kinetic-energy electro n scattering lengths for CF4 and C-C4F8 were found to be -0.180 +/-0.003 nm and -0.618 +/-0.012 nm, respectively. To the best of our knowledge, these are the first measurements of zero-kinetic-energy electron scattering lengt hs for both CF4 and C-C4F8. From these zero-kinetic-energy electron scatter ing lengths, we find that the zero-kinetic-energy electron scattering cross sections are sigma = 4.1 +/-0.2x10(-15) cm(2) and 4.8 +/-0.2x10(-14) cm(2) for CF4 and c-C4F8, respectively.