Discuss the vibration frequency of a diatomic molecule

Question

The mass to use in the expression for the vibration frequency of a diatomic molecule is the effective mass μ =m_Am_B/(m_A+m_B), where m_A and m_B are the masses of the individual atoms. The following data on the infrared absorption wave numbers (in cm^-1) of molecules is taken from Spectra of diatomic molecules, G. Herzberg, van No strand (1950):

 H³⁵Cl         H⁸¹Br           HI               CO            NO
2990         2650           2310           2170          1904

Determine the force constants of the bonds and arrange them in order of increasing the stiffness.