MOLECULAR-ORIENTATION AND SURFACE-MORPHOLOGY IN METHYL-IODIDE FILMS GROWN ON MGO(100) PROBED BY PHOTODISSOCIATION

Photofragments produced following 257 nm irradiation of physisorbed me thyl iodide films on MgO(100) have been-studied using resonantly enhan ced multiphoton ionization coupled with time-of-flight mass spectromet ry. The observed signal is associated with photofragment production fr om methyl iodide chromophores present in the near surface region. Data on the morphology of the evolving film, obtained by monitoring the va riation in photofragment intensity with adsorbate coverage, are consis tent with an overlayer that grows by a stochastic process. The depende nce of the velocity distribution of methyl photofragments on ejection angle and polarization of the photolysis beam indicates that the film is composed primarily of an antiparallel arrangement of methyl iodide molecules whose C-I bonds are aligned close to the surface normal.