July 01, 2022, 07:41:16 PM
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Topic: IR Transmission Spectra has an area of no absorbance  (Read 271 times)

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Offline ArchBubbles

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IR Transmission Spectra has an area of no absorbance
« on: June 07, 2022, 02:08:58 PM »
Hi, I synthesised 3-Aminoacetophenone when I had a look at the IR spectra there's an area at 1700cm-1 where it has no absorbance. I've had a look at SDBS spectra and it doesn't appear in theirs. Is this due to some impurities?

Online Babcock_Hall

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Re: IR Transmission Spectra has an area of no absorbance
« Reply #1 on: June 07, 2022, 03:50:22 PM »
Do you mean that there is a region near 1700 wavenumbers that has no absorbance or no transmittance?  Have you assigned most of the signals in the IR spectrum?
EDT
I think that the region where the absorbance is apparently zero is probably an artifact of how the data were processed.
« Last Edit: June 07, 2022, 04:00:45 PM by Babcock_Hall »

Offline mjc123

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Re: IR Transmission Spectra has an area of no absorbance
« Reply #2 on: June 07, 2022, 06:15:37 PM »
This is called the Christiansen effect and is often observed in spectra of coarse powders. It is typically manifested as an asymmetry of peak shape, with an apparent peak in transmission (above the baseline) on the high frequency side of an absorption band. If you grind your sample more finely, you should see more normal-shaped peaks.

Offline ArchBubbles

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Re: IR Transmission Spectra has an area of no absorbance
« Reply #3 on: June 08, 2022, 01:29:48 PM »
Had a look at what you both suggested, never even knew it was a thing. I wish my uni actually told me about this stuff. Thanks for your help

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