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 3.8×10 14 molecules/cm 2 for both wires and ribbons. Initial values of average sticking probabilities are 0.2 2 for the wire and 0.2 0 for the ribbon at room temperature, and average sticking probabilities abruptly decrease at about 1.7×10 14 molecules/cm 2 . 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 B 1 , B 2 and B 3 are made clear by the multiplex state theory using the above average values. In the B 1 -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 B 2 -state are 0.3 7 and 6 .0 eV. The B 3 -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 B 3 -state.