https://doi.org/10.1351/goldbook.08641
Line width of a molecular spectral band that arises from the probability of spontaneous emission in the absence of radiation fields and interaction with other molecules or entities.
Notes:
- The natural linewidth, measured as the full width half maximum equals \(1/(2\pi c_{0} \Delta t)\), where \(\Delta t\) is the natural lifetime of the excited state.
- If the excited state \(n\) can only emit spontaneously to a single lower state \(m\) the natural linewidth is \(\pu{1.86E-38}\ \tilde{\nu}_{mn}^3 \langle m|\boldsymbol{\mu}|n \rangle^{2}\), when the transition wavenumber \(\tilde{\nu}_{mn}\) is in \(\pu{cm-1}\) and the dipole moment \(\mu\) is in Debye (\(\pu{1D \approx 3.335E-30 C m}\)). In the infrared, typical natural linewidths are approximately \(\pu{E-7 cm-1}\).