We report the first experimental observation of negative ${\mathrm{H}}^{\mathrm{-}}$ ions photodesorbed from a cesiated W(100) surface. The kinetic energy of ${\mathrm{H}}^{\mathrm{-}}$ ions is centered at 1 eV. The relatively flat spectral response of the ${\mathrm{H}}^{\mathrm{-}}$ yield in the 30–100-eV photon energy range suggests that the electronic excitations responsible for ${\mathrm{H}}^{\mathrm{-}}$ desorption involve bonding-to-antibonding level transitions and resonant tunneling within the adsorbate-substrate complex. Cesiation of the W(100) surface was found to be essential for ${\mathrm{H}}^{\mathrm{-}}$ desorption.

• Received 26 May 1988

DOI:https://doi.org/10.1103/PhysRevB.38.8002