  We report ab initio calculations of the dielectric function of six mono- and
bilayer molybdenum dichalcogenides based in a Bethe Salpether
equation+G$_0$W$_0$ ansatz, focussing on the excitonic transitions dominating
the absorption spectrum up to an excitation energy of 3\,eV. Our calculations
suggest that switching chalcogen atoms and the strength of interlayer
interactions should affect the detailed composition of the high 'C' peaks in
experimental optical spectra of molybdenum dichalcogenides and cause a
significant spin-orbit-splitting of the contributing excitonic transitions in
monolayer MoSe$_2$ and MoTe$_2$. This can be explained through changes in the
electronic dispersion around the Fermi energy along the chalcogen series
S$\rightarrow$Se$\rightarrow$Te that move the van-Hove singularities in the
density of states of the two-dimensional materials along the
\textit{$\Gamma$}-\textit{K} line in the Brillouin zone. Further, we confirm
the distinct interlayer character of the '\textsl{C}' peak transition in
few-layer MoS$_2$ that was predicted before from experimental data and show
that a similar behaviour can be expected for MoSe$_2$ and MoTe$_2$ as well.
