Reconstructive phase transitions and effective -adsorbate interactions: H/Mo(100) and H/W(100).

Low Energy Electron Diffraction and Infrared Absorption measurements on H/Mo(100) and H/W(100) indicate that, at very low H coverage (0.04) = theta = 0.3), the effective H-H interactions are very different, leading to island formation on Mo(100) and to a uniform H layer on W(100). This observation suggests that adsorbate induced changes in the substrate lattice are responsible for an additional effective long-range H-H attraction on Mo (100).