  Recent scanning tunneling spectroscopy (STM) experiments display images with
star and ellipsoidal like features resulting from unique geometrical
arrangements of a few adsorbed hydrogen atoms on graphite. Based on
first-principles STM simulations, we propose a new model with three hydrogen
atoms adsorbed on the graphene sheet in the shape of an equilateral triangle
with a hexagon ring surrounded inside. The model reproduces the experimentally
observed starlike STM patterns. Additionally, we confirm that an ortho-hydrogen
pair is the configuration corresponding to the ellipsoidal images. These
calculations reveal that when the hydrogen pairs are in the same orientation,
they are energetically more stable.
