Molecular beam studies on the laser-enhanced reaction of chlorine with a copper surface at 1064 nm

Abstract

The laser-enhanced chemical reaction of Cl 2 with a Cu surface has been investigated using time-resolved mass spectrometry. Mass and time-of-flight (TOF) distributions of the reaction products are measured while a polycrystalline Cu surface is exposed concurrently to a CW supersonic molecular beam of Cl 2 at different translational energies and pulsed laser radiation at 1064 nm. The major neutral desorption products observed in the TOF spectra are Cu 3Cl 3 and CuCl. These TOF spectra can be simulated by Maxwell-Boltzmann distributions. The desorption yields of Cu 3Cl 3 and CuCl have been determined as a function of laser fluence and the translational energy of the incident Cl 2. Both laser fluence and translational energy of the Cl 2 markedly enhance the reaction of Cl 2 with the Cu surface. The mass distribution of the products of the “dark” thermal reaction of Cu-Cl 2 has also been measured by modulated molecular beam mass spectrometry. Cu 3Cl is the dominant product in the thermal reaction with Cu 3Cl 3 and CuCl present in lesser amounts. A possible mechanism for the laser-enhanced reaction of Cu-Cl 2 mainly consists of the dissociative chemisorption of Cl 2 on the Cu surface, diffusion of chlorine into the Cu bulk, and laser stimulated thermal desorption.