  We have performed polarized and temperature-dependent Raman scattering
measurements on extremely large magnetoresitance compounds TaAs$_2$ and
NbAs$_2$. In both crystals, all the Raman active modes, including six A$_g$
modes and three B$_g$ modes, are clearly observed and well assigned with the
combination of symmetry analysis and first-principles calculations. The
well-resolved periodic intensity modulations of the observed modes with
rotating crystal orientations, verify the symmetry of each assigned mode and
are fitted to experimentally determine the elements of Raman tensor matrixes.
The broadening of two A$_g$ modes seen in both compounds allows us to estimate
electron-phonon coupling constant, which suggests a relatively small
electron-phonon coupling in the semimetals TaAs$_2$ and NbAs$_2$. The present
study provides the fundamental lattice dynamics information on TaAs$_2$ and
NbAs$_2$ and may shed light on the understanding of their extraordinary large
magnetoresistance.
