Here's how I interpret it. The energy level at the very top of the table is the true ground state. It is non-degenerate. However, the next two entries have energies very close to the ground state. So, as an approximation, you can lump them in with the ground state. In these three levels, the two electrons in the 2p subshell have their spins aligned. The spin and orbital angular momenta couple to form triplet-P states with different values of total angular momentum J. J = 0 is non-degenerate, J = 1 has degeneracy 3, and J = 2 has degeneracy 5. So, this makes a total of 9 states.
The next entry is a singlet-D level and may be considered as the first excited state. The "outer" two electrons are still in the 2p subshell, but they now have opposite spins and the orbital angular momenta couple to form a total angular momentum J = 2. Thus, the degeneracy of this level is 5.
One thing though - The energy of the excited state is listed as 10193 cm^-1. Converting to eV I get about 1.26 eV. This doesn't agree with your 0.82 eV. Maybe I'm goofing up somewhere.
Tom Snyder
________________________________
From: phys-l-bounces@carnot.physics.buffalo.edu on behalf of David Ward
Sent: Wed 4/5/2006 1:43 PM
To: phys-l@carnot.physics.buffalo.edu
Subject: [Phys-l] atomic degeneracies
Quick question- my chemistry-related stuff is so rusty...
I read the statement "The neutral carbon atom has a 9-fold degeneracy
and a 5-fold degenerate excited level at an energy 0.82 eV above the
ground level" in problem 5.6 in the thermal physics book by M.D. Sturge.
I understand the electron configuratin for Carbon, and the problem
itself was pretty easy to do using the degeneracies given, but where
does the 9-fold and 5-fold actually come from? How would I calculate
those degeneraciy numbers? I know it is probably obvious, but I'm
drawing a blank. Any insight - or a place I can look to learn for
myself- will be appreciated.
Thanks!
david
David Ward
Professor of Physics
UNU# 3160
Dept. of Physics
Union University
1050 Union University Drive
Jackson, TN 38305-3697
office (731)661-5241
FAX (731)661-5175
dward@uu.edu
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