The abstraction of chemisorbed deuterium (D) on Si(100) by atomic hydr
ogen (H(at)) is studied in real time. The surface H and D coverages ar
e measured by mass analyzing the recoiled H+ and D+ ion signals during
the abstraction reaction. We find that H(at) efficiently removes adso
rbed D on Si(100) with a low activation energy of 0.8+/-0.6 kcal/mol a
nd a reaction probability that is 0.36 times the H(at) adsorption rate
on clean Si(100).