From harry %-% at %-% wpcs01.phys-chemie.uni-wuerzburg.de  Fri Sep 18 15:30:50 1992
Date: Fri, 18 Sep 92 13:30:50 +0200
From: Harald Lanig <harry ^at^ phys-chemie.uni-wuerzburg.dbp.de>
To: CHEMISTRY(+ at +)ccl.net
Subject: Help: Excited states in MOPAC or AMPAC



Dear Netters,

I have started doing geometry-optimisation using semi-empirical methods (AM1)
and have now the task minimizing excited states of heteroaromatic molecules.

Calulating excited states of unsubstituted aromates and heteroaromates
workes quite well, because the calulated HOMO, where an electron is
removed, is a ring-orbital. Difficulties are rising when substituting a H-atom
(of benzene) for example with a SO3- group. Looking at the orbitals in the 
ground-state shows that the HOMO is located on the O-atoms and NOT in the ring.

Now my problem: 
How can I remove one electron of the pi-system to get a normal pi-pi(*)-
exitation ? This is important, because the UV-spectras of the substituted
molecules are just the same as the unsubstituted ones.
(Exciting the side chain (SO3-) will lead into dissociation).

What can I do if the "ring-HOMO" of the molecule is the HOMO-6 or even lower ?
In this case, a CI-calulation will fail (I think).

I hope, somebody can help me.
Please answer via e-mail: harry-!at!-phys-chemie.uni-wuerzburg.dbp.de

Thanks in advance  

Harald Lanig.