What absorbs at 3540 cm⁻¹ in an FTIR spectrum?
A band near 3540 cm⁻¹ can point to several functional groups. Below are the most likely assignments, ranked by how much published evidence supports each — every one traceable to literature (DOI) and cross-validated against our 130,000+ reference spectra and knowledge graph.
Backed by 8 cited sources
Quick answer
A band near 3540 cm⁻¹ is usually interpreted by checking which functional groups repeatedly co-occur there in the literature, then confirming at least one or two additional peaks in the same sample. This page ranks those assignments by accumulated evidence rather than by a single fixed textbook rule.
Possible functional-group assignments
| Functional group | Supporting facts | Cited sources | Top confidence |
|---|---|---|---|
| Hydroxyl (O-H) | 11 | 10 | 1.0 |
| Hydrogen bond | 2 | 2 | 1.0 |
| Water (H2O) | 2 | 2 | 1.0 |
| Phosphate (PO4) | 1 | 1 | 1.0 |
| Carbonate | 1 | 1 | 1.0 |
| Alkyl C-H | 1 | 1 | 1.0 |
Ranking reflects accumulated literature evidence, not a single fixed rule. Always confirm against your sample context.
Possible materials
| Material | Supporting peaks | Overlapping groups | Cited sources |
|---|---|---|---|
| Polystyrene | 3540, 1020, 1600 | Hydroxyl (O-H) | 1 |
| apatite | 3540, 3053, 1640 | Phosphate (PO4), Hydroxyl (O-H), Water (H2O) | 1 |
| bamboo | 3540, 1737, 1731 | Hydroxyl (O-H) | 1 |
Materials are shown only when the same literature pool supports this band and at least one additional characteristic peak.
Spectrum logic
This band becomes meaningful only when read with its neighboring peaks. In practice, analysts first look at the assignments above, then check whether the same sample also shows other peaks expected for the same structural motif. A lone band near 3540 cm⁻¹ is usually not enough for material identification by itself.
Real-world usage
This type of query is common in polymer identification, unknown plastic screening, QC troubleshooting, recycled-material verification, and literature-backed peak assignment review.
Common mistakes
- Treating one isolated band as proof of a material without checking at least one or two supporting peaks.
- Ignoring overlap: multiple functional groups can contribute near the same wavenumber.
- Skipping validation when additives, blends, oxidation, or contamination may distort the spectrum.
Verification advice
When ambiguity remains, validate the hypothesis with DSC, GC-MS, or TGA, especially for blends, degraded samples, and filled polymers.
Literature behind these assignments
-
Hydroxyl (O-H) confidence 1.0
“2) for E⊥c the wavenumber 3540 (OH peak), which is zero when and maximal when total ~1⁄5 Cerro is of that for HAM.”
Clark 等 - 2016 - Quantification of CO2 concentration in apatite DOI: 10.2138/am-2016-5661 -
Hydroxyl (O-H) confidence 1.0
“LLM confirmed rule peak-group candidate”
Della Ventura 等 - 2019 - X-ray Structure Refinement and Vibrational Spectro DOI: 10.3390/cryst9060297 -
Hydroxyl (O-H) confidence 1.0
“The presence of water of crystallization was referenced from absorptions at 3539.8, 3487.1 cm-1 and 3166.7 , which are due to intermolecular and weakly H bonded OH.”
Growth and characterization of calcium hydrogen phosphate dihydrate crystals from single diffusion gel technique DOI: 10.1002/crat.200900700 -
Alkyl C-H confidence 1.0
“ison to FTIR results taken from the outside wall section, no significant disparity between cm-1, treated and untreated specimens was observed at peak 3540 which was associated to Materials2022,15,1544 9of16 C-H functional group as per the a”
Investigating the Effect of Smoke Treatment on Hygroscopic Characteristics of Bamboo by FTIR and Raman Spectroscopy DOI: 10.3390/ma15041544 -
Water (H2O) confidence 1.0
“The water stretching bands of (cid:24)3540 cm-1, cm-1, a liquidlike amorphous phase at and Na 2SO have a remarkable blue shift relative to MgSO and 4 4 (cid:24)3620 cm-1, monomeric water molecules at in which the two”
Wei 等 - 2005 - Observation of the first hydration layer of isolat DOI: 10.1021/jp0453865 -
Hydroxyl (O-H) confidence 1.0
“very weak bands at 3540 and 3450 These bands were also present in photodegraded PS and, according to Mailhot and Gardette [8,9], are due to alcohols and prior to oxidation [14].”
Botelho 等 - 2004 - Enhancement of the thermooxidative degradability o DOI: 10.1016/j.polymdegradstab.2004.05.022 -
Hydroxyl (O-H) confidence 1.0
“The OH stretching band of PVPh extended from 3100 cm-1, cm-1 cm-1, corresponding to the signals of the free OH units at 3540 cm-1 and of the selfto 3600 to 3600 corresponding to the signals of the free OH units at 3540 and of the”
Du 等 - 2022 - Intraand Intermolecular Hydrogen Bonding in Misc DOI: 10.3390/ijms23137018 -
Hydroxyl (O-H) confidence 1.0
“cm-1 paint layers with an OH band at 3540 and the broad X-radiographs taken in 1993 revealed that Munch had”
A non-invasive screening study of varnishes applied to three paintings by Edvard Munch using portable diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) DOI: 10.1186/s40494-019-0327-1
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