  The multiple scattering-based theory of Gaspari and Gyorffy for the
electron-ion matrix element in close packed metals is applied to Im-3m H3S,
which has been predicted by Duan {\it et al.} and Bernstein {\it et al} to be
the stable phase at this stoichiometry around 190 GPa, thus is the leading
candidate to be the phase observed to superconduct at 190K by Drozdov, Eremets,
and Troyan. The nearly perfect separation of vibrational modes into those of S
and of H character provides a simplification that enables identification of
contributions of the two atoms separately. The picture that arises is basically
that of superconducting atomic H stabilized by strong covalent mixing with S 3p
and "3d" character. The reported isotope shift is much larger than the
theoretical one,suggesting there is large anharmonicity in the H vibrations.
Given the relative unimportance of sulfur, hydrides of lighter atoms at
similarly high pressures may also lead to high temperature superconductivity.
