  The functional form of Coulomb interactions in the transition metal
dichalcogenides and other van der Waals solids is critical to many of their
unique properties, e.g. strongly-correlated electron states, superconductivity
and emergent ferromagnetism. This paper presents measurements of key excitonic
energy levels in MoSe2/WSe2 heterostructures. These measurements are obtained
from resonance Raman experiments on specific Raman peaks only observed at
excited states of the excitons. This data is used to validate a model of the
Coulomb potential in these structures which predicts the exciton energies to
within ~5 meV / 2.5%. This model is used to determine the effect of
heterostructure formation on the single-particle band gaps of the layers and
will have a wide applicability in designing the next generation of more complex
transition metal dichalcogenide structures.
