Adsorption and reaction of CH3COOH and CD3COOD on the MgO(100) surface: A Fourier transform infrared and temperature programmed desorption study

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Abstract
The adsorption of acetic acid (CH3COOH and CD3COOD) on the (100) surface of a MgO single crystal has been studied using primarily Fourier transform infrared transmission absorption spectroscopy and temperature programmed desorption(TPD). Acetic acid dissociates upon adsorption on this surface, even at 120 K, forming an adsorbed acetate (CH3COO) species. Upon heating in TPD, some of the acetate recombines with surface hydrogen and desorbs as acetic acid but most undergoes a disproportionation reaction to form acetic acid and ketene (CH2CO) products which desorb. The IR intensities of the vibrational modes of chemisorbed acetate over the temperature range of 425–720 K show a strong polarization dependence on the incident IR light indicating an oriented, monodentate adsorbed species. Consideration of the vibrational frequencies of this species reveals new insight concerning the structure and bonding of the acetate radical on the MgO(100) surface and supports our proposal of a novel bimolecular surface reaction between two adsorbed acetate radicals to form ketene and water.