The decomposition mechanism of trimethylphosphite on Ni(1 1 1)

The chemistry of trimethylphosphite ((CH3O)3P) adsorbed on the Ni(1 1 1) surface has been studied in order to gain insight into the initial steps in the decomposition of alkyl and aryl phosphates commonly used as vapor phase lubricants. The primary products of trimethylphosphite decomposition on the Ni(1 1 1) surface are H2 and CO which desorb at 355 and 400 K with kinetics that are similar to those observed for methoxy (CH3O(ad)) decomposition. In addition a CO desorption feature appears at 620 K consistent with recombination of C and O atoms that must be formed by dissociation of the C–O bonds in some fraction of the adsorbed trimethylphosphite. Other minority species that are observed desorbing from the surface include trimethylphosphite itself, methanol, and formaldehyde. This suggests that the major pathway for decomposition is one in which the P–O bonds in trimethylphosphite are cleaved initially to yield the methoxy species. Of the methoxy groups in trimethylphosphite one third undergo C–O dissociation, either as methoxy groups on the Ni(1 1 1) surface or while still bonded to phosphorus. Following heating to temperatures in excess of 700 K the Ni(1 1 1) surface is left clean of all adsorbed species other than phosphorus atoms. The use of trimethylphosphite serves as a simple, clean method for controlled deposition of phosphorus onto the Ni(1 1 1) surface.