Abstract
The measurement of infrared chemiluminescence of the nascent CO2 molecules desorbed in molecular-beam surface reactions has been made to study the dynamics of HCOOH decomposition and HCOOH oxidation on metal surfaces (Pt, Ni). The formation of CO2 in CO oxidation is a bimolecular process (i.e., the LH type reaction between CO(ad) and O(ad)), and vibrationally and rotationally excited CO2 molecules are desorbed from the metal surfaces. In contrast, the CO2 molecules produced by HCOOH decomposition on Pt(or Ni) are not so much excited as those by CO oxidation. The CO2 is formed via decomposition of HC00(ad) (a unimolecular process) with the internal energy distributions as being in equilibrium with the surface temperature. The CO2 formed by HCOOH oxidation (HCOOH+O2 reaction) on the Ni surface is not excited, indicating that the dynamics of the CO2 formation is similar to that of the HCOOH decomposition. On the Pt surface, however, the CO2 is excited substantially, that is, the vibrational and rotational states of the CO2 formed by the HCOOH+O2 reaction are quite similar to those of the CO2 formed by CO oxidation. This finding suggests that the final step of the CO2 formation in the HCOOH oxidation on Pt comprises the bimolecular reaction between CO(ad) and O(ad). The difference in the internal energy distributions of the nascent CO2 can provide us with new information on the dynamics of catalytic reactions.
