ISOTHERMAL RAMPED FIELD-DESORPTION OF BENZENE FROM TUNGSTEN

A new ramped field-desorption technique has been used to investigate the binding of molecular benzene on clean (field-evaporated) tungsten surfaces at 78 K as a function of electric field strength. The resulting spectra, analogous to total pressure thermal desorption spectra, show a physisorbed structure below 0. 36 V/A which increases continuously in area with increasing benzene coverage, a peak at 0. 36 V/A which grows until a saturation coverage is reached (and is thought to represent a physically adsorbed transition layer between chemisorbed and multiple layer physisorbed benzene at the surface), and a series of poorly resolved chemisorbed peaks whose detailed shape depends on the local morphology of the surface region being examined. The crystallographic behavior of the physisorbed and chemisorbed layers on the surface has been visually determined with angstrom resolution.