Subject: Re: CCL: HYBRIDIZATION NOT "REAL"

From: "Oscar N. Ventura" <[email-masked]>
Date: Wed, 13 Sep 2000 08:43:13 -0300 (GRNLNDST)

Dear Jens:

Of course, you are right. I was trying to make another point and
simplified too much. Actually your argument reinforces what I wanted to
point out with my previous (so calld "marxist" :-) argument.

Regards. Oscar

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Prof.Dr.Oscar N. Ventura             Tel.+(5982)9248396 Fax +(5982)9241906
MTC-Lab,Facultad de Quimica          MTC-Lab  http://bilbo.edu.uy/MTC-Lab.html 
Universidad de la Republica
Gral.Flores 2124, C. C. 1157         All opinions are my own, and not
Montevideo 11800, URUGUAY            necessarily those of my employer          

"Violence is the last refuge of the incompetent." --- Salvor Hardin 
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From: "Jens Spanget-Larsen" <[email-masked]>
Date: Wed, 13 Sep 2000 12:03:23 +0100

Oscar N. Ventura:

> Total density (STM), differential density (X-ray), energies of single
> electrons within a molecule (photoelectron spectroscopy) are observable.
> Molecular or atomic orbitals, energies of the molecular orbitals, etc, are
> constructs of the theory and are not observable.

Dear Oscar,

I object to the statement that "energies of single electrons within a molecule 
(photoelectron spectroscopy) are observable".  In photoelectron spectroscopy 
you observe differences in energy between the ground state of the neutral 
molecule and the different electronic states of the molecular radical cation.  
That is, you observe differences in energy between many-electronic states, not 
single electron energies.  If you assume the validity of Koopmans' 
approximation (briefly: adopt the MO model and assume the same set of MO 
functions for the neutral molecule and the radical cation), the ionization 
energies of a closed-shell molecule can be set equal the negative of the 
energies of the occupied canonical MOs.  This result is usually referred to as 
"Koopmans' theorem", but it is only valid within the above-mentioned 
approximations.  The errors involved in these approximations tend to cancel 
each other out and "Koopmans' theorem" is thus very useful in the 
interpretation of photoelectron spectra.  But the underlying assumptions 
frequently break down, leading to inapplicability of the approximate 
one-electron picture of ionization.  

Yours, Jens >--<
                             
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JENS SPANGET-LARSEN         Phone:  +45 4674 2000  (RUC)
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