  We present a theory for site dilution in the Valence Bond Crystal Phase of
the Kagome Lattice Heisenberg Model. The presence of an empty site leads to
strong singlet bond across the impurity. It also creates a free spin, which
delocalizes inside the unit cell. Finite concentration of quenched impurities
leads to a Valence Bond Glass phase. This phase has short-range Valence Bond
order, no spin-gap, large spin susceptibilities, linear specific heat due to
two-level systems, as well as singlet and triplet excitations that decompose
into kink-antikink pairs delocalized over a few lattice constants. It provides
a framework for a comprehensive understanding of thermodynamic, neutron, and
Raman measurements in the Herbertsmithite material ZnCu3(OH)6Cl2, including
recently reported H/T and omega/T scaling.
