HYDROGEN-INDUCED MISSING-ROW RECONSTRUCTION OF FE(211)

We present quantitative structure determinations by tow energy electro n diffraction of both the clean Fe(211) phase and a drastic (1 x 2) re construction induced by hydrogen under thermal activation. For the cle an surface we find a registry shift between the first two atomic layer s and an oscillatory multilayer relaxation in agreement with earlier w ork. The reconstructed (1 X 2) phase is shown to be of the missing row type, whereby every second close packed atomic row is removed. The Pe ndry R-factors, R = 0.16 and 0.19 for the clean and reconstructed surf ace respectively, are convincingly low. Additionally, the missing row reconstruction accounts quantitatively for the observed brightness of extra diffraction spots. The removal of atomic rows entails considerab le movements of second and third layer iron atoms, i.e. pairing and bu ckling.