SURFACE PHOTOCHEMICAL DETERMINATION OF THE MEAN FREE-PATH OF SUBVACUUM ELECTRONS IN ADSORBATE FILMS

Dissociative electron attachment (DEA) of adsorbates was used to detect photoexcited substrate electrons with energies below the vacuum level. When adsorbate layers of variable thickness were deposited on a Pt(111) surface and capped with a topmost, DEA active, detector layer Of CH3Br the mean free path of substrate derived electrons could be measured. The averaged electron scattering cross section through solid Xe at 25 K was sigma(s) = 4.7(-0)+0.7 angstrom2 for electrons of energy -0.6 less-than-or-equal-to E(v) less-than-or-equal-to-0.27 eV with respect to the vacuum level. The cross section in solid CH3Br at 25 K was sigma(s) greater-than-or-equal-to 4.7 angstrom2 averaged over an approximately 0.4 eV FWHM range of electron energies centred at E(v) = -0.7 eV.