The effect of the individual adsorbed states of CO on the work function of polycrystalline tungsten has been examined. The β2 and β3 states are adsorbed simultaneously and together increase the work function φ by 0.33 V at 300°K. At this temperature, the α state begins to fill before the completion of the β1 state, but the total effect of the three β states on φ is estimated as +0.6 V. At 700°K, where the α state is absent, addition of the β1 state to a surface previously filled with β2 and β3 gives a composite layer of lower mean dipole moment, corresponding to a work function increase of 6.3 × 10-16 V/mol. cm2, compared with 14.9 × 10-16 V/mol cm 2 for the β2 + β3 states. It is proposed that the β1 state is involved in a clustering process. The α state changes the work function by approximately -0.1 V (-2.8 × 10-16 V/mol cm2) and at high ambient pressures can compete for β1 sites, thereby reducing the observed maximum work function change. Initial sticking probabilities of unity are observed at 300°K. Reasons for the discrepancy with earlier work are discussed and a mechanism for the filling of the various adsorbed states is proposed. As the adsorption temperature increases the initial sticking probability falls, showing marked decreases at temperatures where the α and β1 states become depopulated.
All Science Journal Classification (ASJC) codes
- Physics and Astronomy(all)
- Physical and Theoretical Chemistry