inertial defect 

https://doi.org/10.1351/goldbook.I03028
Difference of principal moments of inertia Δ=IC−IA−IB. For planar molecules it is close to zero and for non-planar molecules it is negative.
Source:
Green Book, 2nd ed., p. 23 [Terms] [Book]
Citation: 'inertial defect' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.I03028 RIS BibTex EndNote
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Last revised: February 24, 2014