Rotational constants

{
  "id": "MLC-T-CHM-010421",
  "term": "Rotational constants",
  "field": "Chemistry",
  "definition": "The constants A, B and C that set the spacing of a molecule's rotational energy levels, each equal to a fixed factor, h divided by 8π²c, over one of the three principal moments of inertia. Because each is inversely related to a moment of inertia, a heavier or more extended molecule has smaller constants. They are obtained from microwave and rotational Raman spectra, and from them bond lengths and angles are derived.",
  "subject": "Physical and Biophysical Chemistry",
  "see_also": [
    "Planck constant",
    "principal moments of inertia",
    "term"
  ],
  "references": [
    "Green Book, 2nd ed., p. 23 (https://goldbook.iupac.org/files/pdf/green_book_2ed.pdf)"
  ],
  "url": "https://mlchart.com/terminology/chemistry/rotational-constants/"
}