https://doi.org/10.1351/goldbook.08248
The appearance of peaks at incorrect frequencies in a mathematically-processed spectrum due to insufficient density of datapoints in the time-domain spectrum or from peaks outside of the sampled frequency range.This process can be simulated by folding a spectrum that shows the correct wavenumbers back onto itself at \(\tilde{\nu}_{\rm{M}}\) and its multiples.
Notes:
- Folding is a consequence of undersampling in spectroscopy.
- In vibrational spectroscopy, when a spectrum is sampled correctly only up to a wavenumber \(\tilde{\nu}_{\rm{M}}\), radiation of wavenumber \(\tilde{\nu} \gt \tilde{\nu}_{\rm{M}}\) appears to have a wavenumber between 0 and \(\tilde{\nu}_{\rm{M}}\), per the table below:
See also: Nyquist criterion
| Range of wavenumber _013501_ | _026251_ |
|---|---|
| [_013335_, 2_013335_] | 2_013335_ - _013501_ |
| [2_013335_, 3_013335_] | _013501_ - 2_013335_ |
| [3_013335_, 4_013335_] | 4_013335_ - _013501_ |
| [4_013335_, 5_013335_] | _013501_ - 4_013335_ |