  We address the question of the reliability of the Born-Oppenheimer (BO)
approximation for a mass-imbalanced resonant three-body system embedded in
noninteger dimensions. We address this question within the problem of a system
of currently experimental interest, namely $^7$Li$-^{87}$Rb$_2$. We compare the
Efimov scale parameter as well as the wave functions obtained using the BO
approximation with those obtained using the Bethe-Peierls boundary condition.
