Adsorbed films of methyl halides on magnesium oxide and boron nitride
Adsorption isotherm techniques and x-ray powder diffraction were used to study adsorbed films of three methyl halides (CH3R, R=Cl, Br, I) on magnesium oxide (MgO) and boron nitride (BN). The aim of these studies was to gain a better understanding of the behavior of polar molecules under the influence of substrates with different surface geometry. Volumetric adsorption isotherms were used to determine the adsorption areas of the substrate, the molecular areas of the adsorbate and some thermodynamic quantities of the adsorbed system such as the isosteric heat of adsorption and the 2D compressibility. In addition, layering transitions and the wetting behavior near the triple point were investigated for CH3Cl on MgO and BN and for CH3Br and CH3I on MgO. X-ray powder diffraction was used to determine the structural properties of monolayers of methyl halides adsorbed on both substrates. The use of an image plate detector system was employed for the first time in studies of adsorbed films. Temperature and coverage dependent measurements were undertaken to investigate the monolayer structures of CH3Cl, CH3Br and CH3I on MgO and BN.