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Unformatted text preview: tions Relative(arb. units)
Sij Emission Intensity Multiple Transitions
0.02 CO - wave
2000 K 0.01 0
– can simply
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
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
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
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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.
- Summer '08