The quantized @[email protected] of a molecule in its electronic ground or @[email protected] can be approximated with sufficient accuracy for analytical purposes by: \[E_{\text{int}}=E_{\text{el}}+E_{\text{vib}}+E_{\text{rot}}\] where \(E_{\mathrm{el}}\) is the electronic, \(E_{\mathrm{vib}}\) the vibrational and \(E_{\mathrm{rot}}\) the rotational energy, respectively.