What absorbs at 405 cm⁻¹ in an FTIR spectrum?

Quick answer

A band near 405 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

Ranking reflects accumulated literature evidence, not a single fixed rule. Always confirm against your sample context.

Possible materials

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 405 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

• N-O bond confidence 1.0

  “This N-O bond is also proved by XPS on deconvolution peaks detected at 404.8 and 531.5 eV in N 1s and O 1s, respectively.”

  Azami 等 - 2017 - Formation of predominant interstitial N-TiO2 using DOI: 10.5004/dwt.2017.21496
• Hydroxyl (O-H) confidence 1.0

  “Evolution of the OH-stretching region (sample 405) as a and/or ◦Cto390 ◦C ◦C.”

  Della Ventura 等 - 2008 - The P2(1)mC2m phase transition in synthetic am DOI: 10.1127/0935-1221/2008/0020-1836
• Metal sulfur confidence 1.0

  “LLM confirmed rule peak-group candidate”

  60MeV Ni ion induced modifications in nano-CdS/polystyrene composite films DOI: 10.1016/j.radphyschem.2013.06.022
• N-O bond confidence 1.0

  “5 we have reinvestigate the infrared spectrum of the gaseous assigned to Mn C O bending vibrations and band observed at 425cm-1 sample of these compounds which are known to be pure, so that 416, 418, belong to Mn C axial stretching vibratio”

  Mahmood 等 - 2006 - Comparative vapour phase FTIR spectra and vibratio DOI: 10.1016/j.saa.2005.11.024
• Metal sulfur confidence 1.0

  “And peak of the Cd-S bond at 405 was observed, which further testified the generation of CdS nanoparticles.”

  Wang 等 - 2007 - Synthesis and characterization of CdSPVA nanocomp DOI: 10.1016/j.apsusc.2007.04.020
• Silicon-oxygen (Si-O) confidence 1.0

  “Analysis In sample MY33, the occurrence of hematite, Fe 2O 3, with the Raman bands at 227, cm-1 294, 411, 612 and 681 [49] (Figure 7a), vermillion with the Raman signals at 253, cm-1 285 and 341 [50] (Figure 7b), quartz (SiO 2) with the ban”

  Amadori 等 - 2021 - Organic Matter and Pigments in the Wall Paintings DOI: 10.3390/app112311441
• confidence 1.0

  “The larger intensity peak at 400.76 eV results from the two outer nitrogen atoms of the azide functional group, and the smaller peak at 404.8 eV (assigned to azides) is characteristic of the electron poor middle nitrogen [20,21].”

  Awada 和 Daneault - 2015 - Chemical Modification of Poly(Vinyl Alcohol) in Wa DOI: 10.3390/app5040840
• confidence 1.0

  “Peak at 404.8 eV of N 1s represented as surface functional group shows the bonded between nitrogen and adsorbed nitrogen species which is the nitrogen species TiO 2.”

  Azami 等 - 2017 - N-doped TiO2 Synthesised via Microwave Induced Pho DOI: 10.17576/jsm-2017-4608-17