Hydrogen iodide dipole moment

The disparity between the MO coefficients, a and 6, indicates ionic character in every instance the dipole moment of hydrogen chloride is 1.03 D. Infra-red absorption spectra indicate a bond length of 1.26 A, so that, were the molecule completely ionic [i,e, H+Ch), the value of // would be 1.26 X 4.80 = 6.05 D. In fact, the bonding is mainly covalent in the free molecule. If the degree of polarity is measured by 1.03/6.05 == 0.169, it could be said that the bond in HCl is about 83% covalent. On this basis hydrogen iodide would be 95% covalent, the corresponding polarity being 0.05. 

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