Electron transmission through layers of H2O and Xe in the ultrahigh vacuum photoreduction of CH3Cl on Ni(111)

The photoreduction of CH3Cl was used to detect the transmission of electrons through layers of H2O and Xe on Ni(111) under ultrahigh vacuum (UHV) conditions. At a laser wavelength of 248 nm with H2O spacers, the electron intensity exhibited a nearly exponential decay to zero signal with the 1/e point at about 2 monolayers. At 193 nm with H2O spacers, the signal decayed with the 1/e point at about 4 monolayers to a constant value due to the direct photofragmentation of the CH3 Cl possible at this wavelength. At 248 nm with Xe spacers, the signal decayed by a factor of 4 in the first 2 monolayers, after which the signal was nearly constant and nonzero for at least 64 monolayers, indicating a long electron mean free path. CH3Br is shown to behave similarly with H2 O spacers at 248 nm.