New studies reveal fingerprints of reaction mechanisms for the liberation of methane on copper

Several common chemical processes, such as corrosion and heterogenous catalysis, occur at gas-surface interfaces. Because many such reactions proceed through multiple pathways, interest continues to grow in the dynamics of these surface reactions. Since it is difficult to distinguish these pathways experimentally, theoretical first-principles studies provide valuable insights and understanding. This approach has revealed new information about Eley-Rideal (ER) type processes, a common reaction process that forms molecules at the gas-surface interface.

Using direct dynamics studies of a prototypical ER process on a copper surface, Zhou et al. demonstrated the possibility to identify microscopic fingerprints of reaction mechanisms based on reaction product state distributions. As their article in The Journal of Chemical Physics describes, the authors examined the umbrella vibrational modes of methane molecules that have been liberated from a copper (111) surface by hydrogen attacking them while adsorbed. Analyzing the differences in product distributions for these vibrational mode measurements allowed them to determine which mechanisms were at play.

According to the results, when deuterium attacked adsorbed deuterated methyl (CD₃) groups, two mechanisms led to free deuterated methane (CD₄) molecules. Following direct Eley-Rideal processes, if the deuterium atom struck the methyl group on top, the methyl’s umbrellalike shape would invert. Alternatively, if a “hot” deuterium atom first bounced on the copper surface and struck the methyl group from below, the methyl group would become deuterated without an inversion occurring. The authors hope next to confirm their theoretical findings experimentally.

Source: “Communication: Fingerprints of reaction mechanisms in product distributions: Eley-Rideal-type reactions between D and CD₃/Cu(111),” by Linsen Zhou, Bin Jiang, Maite Alducin, and Hua Guo, Journal of Chemical Physics (2018). The article can be accessed at https://doi.org/10.1063/1.5039749 .