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I have run a sample of Pyrene in Ethanol and got a UV Vis absorbance spectra that starts climbing as it reaches the lower wavelengths. I am using quartz cuvettes and was wondering what could be the cause of this rise at the shorter wavelengths.

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Here is the literature spectra.

enter image description here Here is my measured spectra.

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  • $\begingroup$ Please add more instrumental details. Is it a single beam instrument or a double beam instrument. What was your blank? $\endgroup$
    – ACR
    Commented Dec 4, 2023 at 5:30
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    $\begingroup$ the solvent and quartz of your cell (depending on type of quartz) will start absorbing at shorter wavelengths. You can minimise this to some extent using a matched blank cell. $\endgroup$
    – porphyrin
    Commented Dec 4, 2023 at 8:53
  • $\begingroup$ @AChem it is a double beam instrument, however on this test run I did not use a blank $\endgroup$
    – Ashwin
    Commented Dec 9, 2023 at 8:20
  • $\begingroup$ You should not use air as a blank. $\endgroup$
    – ACR
    Commented Dec 9, 2023 at 17:20

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If you had given the reference for the literature spectra, I would be able to say for certain, but it's possible that they didn't use a quartz cuvette. According to this website, quartz starts absorbing below ~200 nm. Looks like it depends on the type of quartz, and brand of cuvette, you've used (from this link):

Different quartz types

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  • $\begingroup$ At wavelengths shorter than $200$ nm, everything absorbs the light, even glass, water or air. Absorption spectrum at these wavelengths must be determined in a vacuum. $\endgroup$
    – Maurice
    Commented Dec 4, 2023 at 14:23
  • $\begingroup$ @Maurice it didn’t occur to me how high that energy was (I’m used to working in wavenumbers)… but yeah, that makes sense $\endgroup$
    – isolated matrix
    Commented Dec 4, 2023 at 17:04

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