  It is shown that the Weyl semimetal TaAs can have a significant polar vector
contribution to its optical activity. This is quantified by ab initio
calculations of the resonant x-ray diffraction at the Ta L1 edge. For the Bragg
vector (400), this polar vector contribution to the circular intensity
differential between left and right polarized x-rays is predicted to be
comparable to that arising from linear dichroism. Implications this result has
in regards to optical effects predicted for topological Weyl semimetals are
discussed.
