π-bonded dimers, preferential pairing, and first-order desorption kinetics of hydrogen on Si(100)–(2×1).

Evidence is presented that π-bonding is present in the surface dimers on clean Si(100)–(2×1) and, as a consequence, that hydrogen atoms preferentially pair on surface dimer atoms even at low coverage. We propose a simple lattice gas model in order to calculate the equilibrium distribution of doubly- and singly-occupied dimers as a function of coverage and temperature, and show that even a very conservative estimate of the enthalpy difference between hydrogen on doubly- and singly-occupied dimers can explain the observed first-order desorption kinetics. [ABSTRACT FROM AUTHOR]