Determine the force constants of the bonds

Question

The mass to use in the expression 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 for the vibration frequency of a diatomic molecule. The following data on the infrared absorption wave numbers of molecules are taken from the 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 stiffness.