physical chemistry question.

Q. The rotational spectrum of HF has lines 4190m1 apart. Calculate moment of inertia and bond length in HF. Q. Which of the following molecules can have pure rotational spectrum? CO2,Br2,N2,NO,N2O,CH4,NH3,H2O,H2O2 Q. Which diatomic molecules should have the closely spaces rotational levels? H2,N2,O2,I2