Adsorption and geometry of 1,4-dioxane on Cu(1 0 0)

The 1,4-dioxane adsorption and geometry on Cu(1 0 0) as functions of coverage and temperature have been studied by temperature-programmed reaction/desorption and reflection-absorption infrared spectroscopy. 1,4-dioxane is adsorbed reversibly on the surface with monolayer desorption at 212 K and multilayer desorption at ∼ 165 K at 4 L exposure. Below ∼ 1.5 L exposure, i.e. 0.6 monolayer coverage, 1,4-dioxane molecules are adsorbed with the ring approximately parallel to the surface. C-H⋯Cu interaction is evidenced by the C-H vibrational mode softening of 2811 cm^-1. Increasing 1,4-dioxane exposure leads to tilted geometry for some of the adsorbed molecules: ∼ 50% at a monolayer coverage at 110 K. However, the monolayer structure is not closely packed at 110 K, most of the tilted molecules change to flat-lying geometry as the surface temperature is increased to 165 K just prior to the onset of molecular desorption.