24 MolecularSpectra

Units sij emission intensity multiple transitions 004

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Unformatted text preview: tions Relative(arb. units) Sij Emission Intensity Multiple Transitions 0.04 0.03 0.02 CO - wave (Rotations) 2000 K 0.01 0 – can simply 0 50 100 150 200 250 “sum” them Wavenumber (cm ) (line-by-line calculations) Pure rotational spectrum -1 Total light absorbed at all frequencies, sum up a ll the lines. Molecular Spectra -6 Copyright © 2009 by Jerry M. Seitzman. All rights reserved. av Why does it have this shape? Can all rotation levels transition to other rotation levels? - No (microwaves) (VII.27) av ,ij Sij ij 300 Assuming Equil, you g et a Boltzman d istribution the e nergy is changing i +/- an energy level. A lso explains the p eak b/c Boltzmann a nd degenercies g, a nd population d istribution !"#$%$ Notice here @ high Absorption Coefficient is related to the number density, Temperature (poulation d ensity, Boltzmann, species composition). Bij is the Einstein Coefficient and it something that is measured and sometimes can be predicted for certain molecules freq. it's going back to zero. That's b ecuse it's like j=40 g oing to j=41. There's not very many so there's no a bsorption 3 At the same freq (say 5150), 3 different absorption coeffcients based on 3 different temperatures. Why? ni (population is changing because T changes density). As I raise the T it goes down (these could be low j's). Collision broadening usually wins at high T Assuming pure water (steam). Blue to red. a goes down. That suggests blue are h igher j lines. When I go from 1300 to 2200, the b roadening brings the p eak down and dominates the Boltzmann fraction. When I go out of the microwaves in the IR, what h appens to the spectrum? There's a lot more stuff.It's complicated mostely b ecause water has more rotational structure 5 00 nm = 20,000 wave numbers. School of Aerospace Engineering We're at 2 microns (IR) -> Vib + Rot. It's complicated looking b ecause water has vibration, j changes can be 0 and +/- 1. The d elta V. Example: H2O • Using HITRAN/HITEMP database for Sij 0.06...
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This note was uploaded on 02/27/2014 for the course AE 6050 taught by Professor Staff during the Summer '08 term at Georgia Tech.

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