Calorimetric Studies on Chemisorption of Nitrogen on Tantalum

Behaviors of chemisorption of wires and ribbons are studied with Roberts' type adsorption calorimeter. The total saturation coverages are 3.8×1014 molecules/cm2 for both wires and ribbons. Initial values of average sticking probabilities are 0.22 for the wire and 0.20 for the ribbon at room temperature, and average sticking probabilities abruptly decrease at about 1.7×1014 molecules/cm2. Average calorimetric heats also vary with the increase of coverage as 6.7, 6.0 and 5.2 eV for the wire, and 7.3 and 5.4 eV for the ribbon. Properties of the chemisorption states of B1, B2 and B3 are made clear by the multiplex state theory using the above average values. In the B1-state, the sticking probability is very small such as 0.01 and the heat of chemisorption is also small such as 5.3 eV. These values for the B2-state are 0.37 and 6.0 eV. The B3-state has the largest values of 0.5 and 7.3 eV. The heat of chemisorption of 6.1 eV calorimetrically obtained on an evaporated film is identical with that of the B3-state.