  We investigate the structure and features of an ultralong-range triatomic
Rydberg molecule formed by a Rb Rydberg atom and a KRb diatomic molecule. In
our numerical description, we perform a realistic treatment of the internal
rotational motion of the diatomic molecule, and take into account the Rb($n,
l\ge 3$) Rydberg degenerate manifold and the energetically closest neighboring
levels with principal quantum numbers $n'>n$ and orbital quantum number
$l\le2$. We focus here on the adiabatic electronic potentials evolving from the
Rb($n, l\ge 3$) and Rb($n=26, l=2$) manifolds. The directional properties of
the KRb diatomic molecule within the Rb-KRb triatomic Rydberg molecule are also
analyzed in detail.
