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The binding states and condensation kinetics of CO 2 and its decomposition products CO and O 2 on (100) W are examined by flash desorption mass spectrometry. Carbon dioxide desorbs almost entirely as CO and oxygen at all coverages. At saturation there are three major states of CO. These correspond to the high temperature states of CO alone although all peaks are shifted and amounts are altered slightly. Carbon monoxide exhibits four major binding states. All of these obey first order desorption kinetics as expected except the most tightly bound state which obeys second order kinetics. Desorption from a bimolecular complex is postulated to explain these results. Initial sticking coefficients of CO 2 , CO, and O 2 at 300°K are 0.85, 0.49, and 1.0 respectively. Coverage dependences indicate precursor intermediates for the states occupied at low coverages. The initial sticking coefficient of CO 2 varies rather slowly with substrate temperature, falling to 0.3 at 1200°K.

The binding states and condensation and desorption kinetics of nitrogen on (100) W are studied using flash desorption mass spectrometry. At moderate exposures there exist three states, a tightly bound β2 state and two weakly bound molecular y states ; the saturation densities for each state are 2.5 × 1014 molecules cm−2. Very high nitrogen exposure at low temperatures produces in addition to these states a tightly bound (Ed = 49 kcal mole−1) β1 state which desorbs with first order kinetics and at 300 °K has a sticking coefficient of less than 10−3. Desorption kinetics for the β2 state at high coverages can be explained quantitatively only by assuming a coverage dependent activation energy or pre-exponential factor; the latter is predicted if desorption is limited by surface diffusion controlled recombination of atoms. The binding states and atomic configurations are shown to be reasonable on the basis of the electronic structures of the adsorbate and the substrate ; this predicts the existence of a structure for the β2 state in which alternate sites are occupied and agrees with the measured stoichiometry. The sticking coefficient into the β2 state is measured as a function of coverage and substrate temperature in the interval 195 °K < T < 1035 °K. Condensation appears to proceed via a weakly chemisorbed precursor. Quantitative agreement with the data is obtained using a model in which the sticking coefficient and desorption kinetics of the precursor state are completely independent of the occupation of the β2 state.

The binding states and condensation kinetics of CO 2 and its decomposition products CO and O 2 on (100) W are examined by flash desorption mass spectrometry. Carbon dioxide desorbs almost entirely as CO and oxygen at all coverages. At saturation there are three major states of CO. These correspond to the high temperature states of CO alone although all peaks are shifted and amounts are altered slightly. Carbon monoxide exhibits four major binding states. All of these obey first order desorption kinetics as expected except the most tightly bound state which obeys second order kinetics. Desorption from a bimolecular complex is postulated to explain these results. Initial sticking coefficients of CO 2 , CO, and O 2 at 300°K are 0.85, 0.49, and 1.0 respectively. Coverage dependences indicate precursor intermediates for the states occupied at low coverages. The initial sticking coefficient of CO 2 varies rather slowly with substrate temperature, falling to 0.3 at 1200°K.