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Is my experiment on spectroscopy conceptually correct?

  1. Sep 19, 2007 #1
    I wanted to know that whether my following experiment is conceptually correct or not.

    I am making a project on spectrosopy. And I have created my files and chart and everything the only thing which is left is a working model.

    Now what i am trying to do is to find out the amount of CO2 in air. Suppose we take a sample of air and we pass radiation having the wavelengths ranging from 1 to 50 micrometers, through it. Now CO2 aborbs radiation ranging from 5 to 20 micrometers . Now behind this sample we would keep a photodiode array.Hence the incident radiation would create electricity.

    Now we would rehearse the same experiment again,with the absence of CO2 in the air. And this is what i dont know how to do.

    Now both the times the current produced by the photodidodes would be different.So now if we study the voltage and magnitude of the current for both the experiments which would certainly be different,can we have some way in order to find out that how much amout of radiation is aborbed by CO2 so that we can find the total amount of CO2 in the gas?

    I kow that i would certainly get wise answers and also suggetions which would help me do this experiment properly.
    Last edited: Sep 19, 2007
  2. jcsd
  3. Sep 19, 2007 #2


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    Yes you could do this. It will require you to make up several concentrations of CO2 in pure (no CO2) air. The range should bracket the expected value that you intend to measure. You must then determine if your new spectrometer is sensitive enough to respond to these differences in a reproducible way. Your photodiode must be stable enough to accurately respond to the different concentrations. If it is not, you must tailor the path length in your sample to give you enough CO2 to 'see'. If too much energy is absorbed by the CO2, you must reduce the path length to get enough energy on the photodiode.

    Have you thought about the type of cell you will use for this work? Will plastics absorb in this wavelength range?
  4. Sep 19, 2007 #3


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    You can make air free of CO2 by bubbling air through a strong solution of base like sodium hydroxide. Pass the air through a drying column (use drierite or magnesium sulfate, anhydrous) and then into your evacuated cell.
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