Highlight 1. Consider a linear chain of charged ions with lattice constant a. Also consider that the even numbered ions2na have charge +2e and mass m and odd numbered ions are of charge -2e and mass M. This chain of atoms is subjected to an electric field Ez of a sinusoidal electromagnetic wave of angular frequency propagating along the x-direction: Le., E, Epe(-) a) If the angular frequency as of the EM wave is found in the infrared range, then find out the position of the wave vector of the phonons within the Brilloium zone. Justify your answer. b) Draw a schematice diagram to describe the action of E on the ions and explain your diagram. c) If the propagation term of the field is neglected, write down the equation of motion of the ions under the action of E, with restoring forces limited to nearest neighbors. Determine the dipole moment formed by two consecutive atoms 12+2+2 Er