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In infrared (IR) spectroscopy, peaks appear negative due to the way the instrument measures absorbance. The IR spectrum is typically plotted as transmittance (percentage of light transmitted) versus wavenumber or frequency. When a sample absorbs IR radiation, less light reaches the detector, resulting in a decrease in transmittance, which is reflected as a negative peak on the spectrum. Essentially, the negative peaks indicate specific frequencies at which the sample has absorbed energy.

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2d ago

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Force constant in IR spectroscopy?

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Use an IR spectrophotometer, then check the peaks. :)


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un- in- ir- non- anti- counter- contra-