Problem 20
For solid \(\mathrm{Ba}\left[\mathrm{CSe}_{3}\right],\) the vibrational wavenumbers and assignments for the \(\left[\mathrm{CSe}_{3}\right]^{2-}\) ion are \(802\left(E^{\prime}, \text { stretch }\right), 420\) \(\left(A_{2}^{\prime \prime}\right), 290\left(A_{1}^{\prime}\right)\) and \(185\left(E^{\prime}, \text { deformation }\right) \mathrm{cm}^{-1}\) (a) Based on these assignments, deduce the shape of the \(\left[\mathrm{CSe}_{3}\right]^{2-}\) ion (b) Draw diagrams to illustrate the modes of vibration of \(\left[\mathrm{CSe}_{3}\right]^{2-}\). (c) Which modes of vibration are IR active?
Problem 21
Deduce the point groups of each of the following molecular species: (a) \(\operatorname{SiF}_{4},(b)\left[\mathrm{CO}_{3}\right]^{2-},(c) \mathrm{CO}_{2}\) \((d) \operatorname{Si} H_{2} C l_{2}\)
