  We present an investigation of the lattice dynamics of the
charge-density-wave compound 2H-NbSe2. We analyze the precise nature of the
wave vector dependent electron-phonon coupling (EPC) and derive the bare
dispersion of the charge-density-wave (CDW) soft phonon mode using inelastic
x-ray scattering combined with ab-initio calculations. Experimentally, phonon
modes along the {\Gamma} - M line, i.e. q = (h, 0, 0) with 0 <= h <= 0.5, with
the same longitudinal symmetry ({\Sigma}1) as the CDW soft mode were
investigated up to 32 meV. In agreement with our calculations we observe
significant EPC in the optic modes at h <= 0.2. We analyze the EPC in the optic
as well as acoustic modes and show that the q dependences stem from scattering
processes between two bands at the Fermi surface both having Nb 4d character.
Finally, we demonstrate that the soft mode dispersion at T = 33 K (= {T_{CDW}})
can be well described on the basis of a strongly q dependent EPC matrix element
and an acoustic-like bare phonon dispersion in agreement with observations near
room temperature.
