The standard dissociation energy at zero kelvin

Values of Do calculated from spectroscopic measurements are listed in the sixth column of Table 4.1. The difference between the Do values of the isotopomers H2 and is 

Naturally occurring hydrogen gas contains about 99.96% H2 and about 0.04% 

The difference between the zero point energies of isotopomers of the other molecules in the table is much smaller than between the hydrogen isotopomers. Thus the difference between the zero point energies of Li Li and Li2 is less than 0.1 kJ mol unless accuracies greater than 0.1 kJ mol are required, we may disregard isotope effects on dissociation energies for molecules that do not contain hydrogen. 

Closer examination by the tools of statistical thermodynamics shows that the absolute value of the difference ( RT — always will be less than RT or about 1.2 kJ mol at 298 K in practice, the difference between the dissociation energies at zero and 298 K is usually smaller than their combined experimental uncertainties. 

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