Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Need help with spectra

  1. Apr 7, 2009 #1
    I was not sure if I should post this here or in the Atomic forum (hope its in its right place).

    My task is to plot the "synthetic" emission spectra with help from data provided by the hitemp database (hitran database: http://www.cfa.harvard.edu/hitran/). So, I have several question that have arised.

    In the Hitran database (and other database) they uses an unit on intensity that is [cm-1/( molecule × cm-2 )] How does this work? Isn't intensity usually given in the unit [Wm-2] or [Wm-2sr-1]?

    What is intensity of a spectral line? I guessing it is the absorbance you are measuring and not the intensity with a spectrometer?

    As I said I would like to plot the emission spectra. I have been told it is not the inverse of the absorption spectra (due to photons lost by quenching, collisions, ionizations etc.)? So how do I do this?

    I am provided with following parameters..

    M = Molecule number
    I = Isotopologue number
    v = Vacuum wavenumber
    S = Intensity [ cm^1/(molecule cm^2) at standard 296K
    R = Weighted square of the transition moment
    A = Einstein A-coefficient
    gair = Air-broadened half-width
    gself = Self-broadened half-width
    E00 = Lower-state energy
    nair = Temperature-dependence exponent for gair
    dair = Air pressure-induced line shift
    V0 = Upper-state ‘‘global’’ quanta
    V00 = Lower-state ‘‘global’’ quanta
    Q0 = Upper-state ‘‘local’’ quanta
    Q00 = Lower-state ‘‘local’’ quanta
    g0 = Statistical weight of the upper state
    g00 = Statistical weight of the lower state

    I am able to plot the spectra from the data that is provided by the hitran database in matlab (but then I plot the value S as the maximum value of line.. and sum the "intensities" if there are spectral lines that are "on top" of each other). I would like to plot the the emission spectra, but according to definition in the "HITRAN paper describing 1996 edition" the intensity S is the integrated area of the spectral line. (shapded area of the line). I am guessing this is neither absorption or emission?? Or??

    The lines you see in a spectra is that the absorbance or the emission that you register and not the intensity? Do you see my confusion? I guess one have to try to determine the absorbance from the hitran or???

    I am thinking that maybe one could use the "Kirchhoffs law" (e=1-r) to plot the emission line or maybe the Beer -Lambert Law?? Does anyone have a clue?

    gosh, I am so confused.

    Any help would be very much appriciated.
     
  2. jcsd
  3. Apr 17, 2009 #2
    If this is homework you should post this in the homework section of the forums.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Need help with spectra
  1. Need A Help ! (Replies: 2)

Loading...