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Decided to make my chemistry project on spectroscopy

  1. Aug 31, 2007 #1
    Hi
    I have decided to make my chemistry project on spectroscopy. I have included optical spectroscopy,Molecular spectroscopy,Resonance spectroscopy and X ray spectroscopy. Molecular spectroscopy includes microwave,raman,visible,stark,photoelectron and etc
    I am in the 11th standard ie 16 years old. So according to my age limit i want some information that how can i make a working or a non working model related to spectroscopy.I would also like to know that which topics should be included while making charts.
    I hope that you all reply soon.Its really urgent.
     
  2. jcsd
  3. Aug 31, 2007 #2

    Gokul43201

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    It's not clear what you mean by "model"? Also, we don't know how big/extensive this project is supposed to be. Are there any guidelines that have been given to you? How much time are you expected to devote to this project?

    To understand most concepts in spectroscopy, you would need a reasonable grounding in quantum mechanics. Some concepts, however, like the essential features of vibrational spectra (Stokes and anti-Stokes lines in Raman, the Rayleigh and IR peaks), can be developed mostly from classical E&M. This may or may not be accessible to you, depending on your present physics preparedness, but it's probably at the advanced high school/early college level.

    The application of spectroscopy for identification of inorganic molecules or organic functional groups can be discussed at your level if you choose not to go down to the mechanisms.
     
    Last edited: Aug 31, 2007
  4. Aug 31, 2007 #3

    chemisttree

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    Here is an idea that you might try. You will need to research it yourself since it is your project. A spectrometer is a device that analyzes a sample's interaction with a spectrum of energies. An infrared spectrometer will analyze the sample's absorption of infrared energy of varying wavelengths. A 'visible' spectrometer will analyze the sample's absorption of visible light. This is accomplished using a rather expensive diffraction grating on commercial instruments. The source radiation (light bulb) contacts the diffraction grating and a rainbow is reflected off the surface. If either the grating's angle from the source to the sample is changed or the position of the sample and detector is moved, the radiation of a narrow band of colored visible light is allowed to strike the sample. The radiation passes through the sample and a fraction of it is absorbed. That fraction of the narrow band of colored visible light that is not absorbed passes through the sample and strikes the detector which converts the energy into either a voltage or a small current. The signal of the detector is recorded continuously as the narrow band of colored light is swept through the visible spectrum (violet to far red). The resulting absorption spectrum is somewhat unique for each sample that has a visible absorption... another way of saying it's colored.

    Like I said, the diffraction grating is rather expensive but you may find that a prism would work. Fix the prism on a bearig of some sort that has a pointer that points to a graduated scale... a good application for that (almost) useless protractor you aren't using anymore. Alternatively you could use a series of colored LED lamps. I would use three at evenly spaced points in the visible spectrum. One blue, one yellow and one red. You will need to research the wavelengths given off by each of these. You might want to throw in an IR LED as well (that is 'near infrared' to the spectroscopist). It is up to you to determine how to wire and power the thing. You will need to think about a sample holder and a sample 'cuvette'. Choose one that doesn't absorb in the frequency range you will span (no red or blue test tubes!). Alternatively you could use a series of filters... one red, yellow and blue, with a white LED. An array of photodiodes with a built in filter over each of the tiny pixel elements is termed a 'photodiode array'. (http://elchem.kaist.ac.kr/vt/chem-ed/optics/detector/pda.htm)

    You could also use your computer monitor. Write a program (you choose the language) to change the color of the screen from blue to deep red. In this case, the spectrometer will consist of a sample holder with an integrated detector (photoresistor). Place a sample of the solvent into the instrument and record the voltage produced when the screen if blue, yellow and red (or choose as many frequencies as you have the energy/stamina). Did I mention that you will need to hold this thing up against your monitor? Replace the blank sample with the actual sample and repeat the process. Record the voltages in an Excel spreadsheet. Subtract the voltage from the sample from the voltage of the blank and plot the result Voila! A crude visible spectrum.

    Or you could just use something like this:

    http://scientificsonline.com/product.asp_Q_pn_E_3052521

    Search "Photodiode array spectrometer"
     
    Last edited: Aug 31, 2007
  5. Aug 31, 2007 #4
    I am very gratefull that you gave your time for my project. But will you do me one favour read the following and if you feel that i have misunderstood the concept than please reply me as soon as possible.
    I am not sure but what you mean is that that we take LEDs as light sources and than we let the light pass through the sample which is kept in a cuvette and then the light which is not absorbed passes over the photodiodes which in turn generate the current and from which we can calculate the frequency of the incident light.Is the concept correct?And what about the responsivity of the diode? And how would dark current play a role here?
    Please reply soon
     
  6. Aug 31, 2007 #5

    chemisttree

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    The detector would be a photodiode (or photoresistor). The source would be a light emitting diode. Two separate diodes here. One provides a relatively pure color (Blue, Yellow, Red) that is attenuated by the sample and passes to the separate photodiode (or photoresistor) detector. The signal is read from the photodiode (or photoresistor) detector. Hopefully the dark current would introduce a constant bias to the signal that would be subtracted out from comparing the blank to the sample.
     
  7. Sep 1, 2007 #6
    But would the frequency of the light from the LEDs would be sufficient to cause the necessary effect in the photodiodes. Or we can take a normal tugnsten bulb and then we can use a prism and then we can use filters and let only the light which we want incident on the sample and so on.
    Can this thing (the bulb thing) work?
     
  8. Sep 4, 2007 #7

    chemisttree

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    The tungsten bulb can work. You will be working with higher voltage of course. Be careful.

    BTW, Don't try the monitor idea. I don't think the light will be monochromatic enough for your use. The LED idea might work by substituting the LED for the tungsten bulb. I believe that the LED light is monochromatic enough for a crude spectrometer but you will need to find out. Try passing the LED light through a prism and look for any other colors.
     
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