From owner-chemistry@ccl.net Thu Apr 21 17:35:00 2011
From: "Steve Williams willsd_._appstate.edu" <owner-chemistry]![server.ccl.net>
To: CCL
Subject: CCL: Hund rule
Message-Id: <-44452-110421125108-30979-o6QdU0kPSCDdHYuddmRVVA]![server.ccl.net>
X-Original-From: Steve Williams <willsd*|*appstate.edu>
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Date: Thu, 21 Apr 2011 12:43:19 -0400
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Sent to CCL by: Steve Williams [willsd__appstate.edu]
Here is a crude rationalization:
If electrons have parallel spins, they MUST occupy different spacial 
orbitals, else the Pauli principle would be violated.  Different spacial 
orbital occupation suggests reduced likelyhood of these electrons being 
near each other, and so reduces the electron-electron repulsion.  High 
spin multiplicity implies low repulsion between electrons.
Of course more quantitative explanations involving exchange and Coulomb 
contributions electron repulsion energy are available as well.  Most 
physical chemistry textbooks will a discussion of the 1s2s excited 
configuration of He where this should be discussed.
Steve Williams
On 04/21/2011 11:23 AM, bonoit bonoit bonoit_10%x%yahoo.fr wrote:
> Sent to CCL by: "bonoit  bonoit" [bonoit_10 : yahoo.fr]
> Dear CCLers,
>
> I'm writting to enquire about the Hund rule:
>   "The term with the maximum multiplicity lies lowest in energy"
>
> My question is:
>
> What is the origin of this phenomenun?
>
> Sincerely,
> Bonoit>
>