Thermal and UV photo-induced decomposition of azomethane on Rh(111)

Abstract

The thermal and UV photo-induced decomposition of azomethane, CH₃NNCH₃, was investigated by means of reflection absorption infrared spectroscopy (RAIRS) and temperature-programmed desorption spectroscopy (TPD). The RAIRS data revealed that azomethane adsorbs in the trans-configuration mode on Rh(111) at 90 K. During thermal treatment, azomethane decomposes exclusively by N–N bond scission, yielding H₂, N₂, C₂N₂ and traces of HCN. Upon UV irradiation at 90 K, adsorbed azomethane undergoes tautomerization, forming formaldehyde methylhydrazone, CH₃NHNCH₂. The important features of the post-irradiation TPD spectra are the significant suppression of C₂N₂ and N₂ formation, and the appearance of the new products methylamine (CH₃NH₂) and CH₄. C–N bond scission also occurred in the illuminated chemisorbed layer at 90 K.