08248
folding
IUPAC Gold Book - folding
10.1351/goldbook.08248
08248
current
synonym: aliasing
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1
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.
- 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:
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Nyquist criterion
https://goldbook.iupac.org/terms/view/08275
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undersampling
https://goldbook.iupac.org/terms/view/08297
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vibrational spectroscopy
https://goldbook.iupac.org/terms/view/08708
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wavenumber
https://goldbook.iupac.org/terms/view/08301
- PAC, 2021, 93, 647. 'Glossary of methods and terms used in analytical spectroscopy (IUPAC Recommendations 2019)' on page 659 (https://doi.org/10.1515/pac-2019-0203)
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Citation: 'folding' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. 10.1351/goldbook.08248
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2026-06-30T21:41:42+00:00