What absorbs at 400 cm⁻¹ in an FTIR spectrum?
A band near 400 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 400 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 |
|---|---|---|---|
| Metal oxygen | 21 | 19 | 1.0 |
| Hydroxyl (O-H) | 15 | 15 | 1.0 |
| Amide | 14 | 14 | 1.0 |
| N h | 12 | 12 | 1.0 |
| Alkyl C-H | 10 | 10 | 1.0 |
| Silicon (Si) | 9 | 8 | 1.0 |
| Methacrylate | 8 | 8 | 1.0 |
| Acetate | 8 | 8 | 1.0 |
| Secondary amine | 8 | 8 | 1.0 |
| N-O bond | 7 | 7 | 1.0 |
| Carboxyl (COOH) | 7 | 5 | 1.0 |
| Silicon-oxygen (Si-O) | 6 | 6 | 1.0 |
| Carbonyl (C=O) | 5 | 5 | 1.0 |
| Water (H2O) | 5 | 5 | 1.0 |
| Methoxy (OCH3) | 5 | 5 | 1.0 |
| C-O single bond | 5 | 5 | 1.0 |
| C n single bond | 4 | 4 | 1.0 |
| Amine primary | 4 | 4 | 1.0 |
| Ammonium | 4 | 4 | 1.0 |
| Ketone | 3 | 3 | 1.0 |
| Ester | 3 | 3 | 1.0 |
| C c single bond | 3 | 3 | 1.0 |
| Methyl | 3 | 3 | 1.0 |
| C=n | 3 | 3 | 1.0 |
| Siloxane (Si-O-Si) | 3 | 3 | 1.0 |
| Carbohydrate | 2 | 2 | 1.0 |
| Phosphate (PO4) | 2 | 2 | 1.0 |
| Metal oxo | 2 | 2 | 1.0 |
| Silanol (Si-OH) | 2 | 2 | 1.0 |
| Silicon silicon | 2 | 2 | 1.0 |
| Nitrogen heterocycle | 1 | 1 | 1.0 |
| Metal hydroxyl | 1 | 1 | 1.0 |
| Ring structure | 1 | 1 | 1.0 |
| Alkene (C=C) | 1 | 1 | 1.0 |
| Aromatic ring | 1 | 1 | 1.0 |
| Protein | 1 | 1 | 1.0 |
| Urethane | 1 | 1 | 1.0 |
| Lignin | 1 | 1 | 1.0 |
| Phosphorus | 1 | 1 | 1.0 |
| Carbon dioxide | 1 | 1 | 1.0 |
| Imide | 1 | 1 | 1.0 |
| Hydrogen bond | 1 | 1 | 1.0 |
| Carbonate | 1 | 1 | 1.0 |
| Silicon nitrogen | 1 | 0 | 1.0 |
| Nitride | 1 | 0 | 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 |
|---|---|---|---|
| graphene oxide | 400, 1150, 3400 | Hydroxyl (O-H) | 1 |
| CeO2 | 400, 1554, 1630 | Hydroxyl (O-H), Metal oxygen | 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 400 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
-
confidence 1.0
“The formation of iron oxide NPs was confirmed with these distinctive peaks in the region between [400 and cm-1 600] where these extended peaks corresponded to iron oxide magnetite Fe 3O 4-NPs [30].”
Effect of Ferric Chloride Concentration on the Type of Magnetite (Fe3O4) Nanoparticles Biosynthesized by Aqueous Leaves Extract of Artemisia and Assessment of Their Antioxidant Activities DOI: 10.1007/s10876-020-01868-7 -
Water (H2O) confidence 1.0
“Secondly, the absorp1700-1600cm-1 tion band in region is attributed to the bend vibration of hygroscopic, adsorbed, bound water or structural 400cm-1 OH.”
Cai 等 - 2007 - A Fourier transform infrared spectroscopic study o DOI: 10.1016/j.saa.2006.02.053 -
Metal oxygen confidence 1.0
“The presence of peak at enceofresidualorganicsinthesample.Asignificantspectroscopic 460cm-1 band at 840, 654, 600 and corresponds to Al-O vibrationwhereasbandat400cm-1 correspondstoCe-Ovibration.The 400cm-1 band at 460 [16] and [17] which a”
Chandradass 等 - 2009 - Effect of different fuels on the alumina-ceria com DOI: 10.1016/j.jallcom.2008.12.119 -
Carbonyl (C=O) confidence 1.0
“in the high frequency region with the most characteristic carbonyl vibrations haveusedthelast400nsofeachreplicatosample328geometriesto highlighted.”
Chenchiliyan 等 - 2023 - Ground-state heterogeneity and vibrational energy DOI: 10.1063/5.0135268 -
Silicon (Si) confidence 1.0
“The weak absorption in the near infrared region (~400 cm-1) of three compounds is ascribed to Si-Si bonds.”
Synthesis, characterization and properties of diamidodisilanes and azocyclosilane DOI: 10.1360/982004-590 -
N-O bond confidence 1.0
“Of the success of the functionalization is further Sample O/C Ratio N/O Ratio revealed by the appearance of a new peak at 400 eV (N1s) (Figure 5a), which is further confirmed by”
Daud 等 - 2017 - Functionalizing Graphene Oxide with Alkylamine by DOI: 10.3390/nano7060135 -
Hydroxyl (O-H) confidence 1.0
“Figure 4 compares, as an example, the O-H stretching bands well-defined composition of the sample under study, the main band measured at 400 °C on the studied sample both in situ and after cm-1 M(1)Fe2+M(1)Fe2+M(3)Fe2+-OH at 3678 is assigne”
Deprotonation of Fe-dominant amphiboles: Single-crystal HT-FTIR spectroscopic studies of synthetic potassic-ferro-richterite DOI: 10.2138/am-2017-5859 -
C c single bond confidence 1.0
“The 400 band assigned to C-C-C bending shows a blue shift during heating, suggesting an increase in conformational disorder, cm-1 band assigned to CH twisting shows a red shift owing to an increase in whereas the 1330 2 the interchain dista”
Hiejima 等 - 2017 - Investigation of the Molecular Mechanisms of Melti DOI: 10.24517/00050382
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