Force constant — UPSC CSE 1998 Physics PYQ

Calculate the force constant for the coupling between H and Cl, given that the fundamental frequency of H^1 Cl^{35} molecule is 8.7 \times 10^{13}\text{ Hz}. Assuming the force constant of H^2 Cl^{35} to be the same as that of H^1 Cl^{35}, calculate the vibration frequency of H^2 Cl^{35}