  Detailed high pressure Resonance Raman ($RR$) Spectroscopy and X-ray
diffraction ($XRD$) studies are carried out on 3-4 layered $MoSe_2$ obtained by
liquid exfoliation. Analysis of ambient $XRD$ pattern and $RR$ spectra indicate
the presence of a triclinic phase along with its parent hexagonal phase.
Pressure evolution of prominent Raman modes and their full width at half
maximum ($FWHM$) show slope changes at about 13 GPa and 33 GPa, respectively.
Slope change in the linear behavior of reduced pressure ($H$) with respect to
Eulerian strain ($f_E$) is observed at about 13 GPa. A minimum in the $FWHM$
values of $E_{2g}^1$ and $A_{2u}^2$ modes at the same pressure indicate to an
electronic topological transition ($ETT$). Above 33 GPa the sample completely
gets converted to the triclinic structure, which indicates the importance of
strain in structural as well as electronic properties of two dimensional
materials.
