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By Klaus P. Huber and Gerhard H. Herzberg. NIST Chemistry WebBook compilation of diatomic constants.

Cited row: ground $X{}^1{\Sigma }^{+}$ state of hydrogen iodide, ${\omega }_e=2309.014\mathrm{c}{\mathrm{m}}^{-1}$ and ${\omega }_e{x}_e=39.6435\mathrm{c}{\mathrm{m}}^{-1}$. Higher anharmonic coefficients are also tabulated, so the two-constant Morse oscillator extrapolation should not be confused with a measurement of the actual dissociation threshold.

The molecule with the larger inferred dissociation energy is assigned the stronger hydrogen–halogen bond: $\mathrm{A}=\mathrm{HBr}$ and $\mathrm{B}=\mathrm{HI}$. Moving from bromine to the larger iodine atom generally lengthens the bond and reduces effective overlap with the compact hydrogen $1s$ orbital, so hydrogen iodide is more weakly bound. Independently, the tabulated ground-state harmonic constants near $2649\mathrm{c}{\mathrm{m}}^{-1}$ for hydrogen bromide and $2309\mathrm{c}{\mathrm{m}}^{-1}$ for hydrogen iodide agree with the inferred assignment.^[ref][ref] The ordering is the identification criterion; the low-level Morse oscillator extrapolations above should not be presented as measured dissociation energies.