From owner-chemistry@ccl.net Fri Aug 22 15:23:01 2008 From: "John McKelvey jmmckel*_*gmail.com" To: CCL Subject: CCL:G: Determining whether a transition is n-pi* or pi-pi* Message-Id: <-37598-080822131514-7626-wRVe8VpVubvLUsgdRUDTVw.:.server.ccl.net> X-Original-From: "John McKelvey" Content-Type: multipart/alternative; boundary="----=_Part_36727_18474373.1219422391207" Date: Fri, 22 Aug 2008 12:26:31 -0400 MIME-Version: 1.0 Sent to CCL by: "John McKelvey" [jmmckel[A]gmail.com] ------=_Part_36727_18474373.1219422391207 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Content-Disposition: inline One immediate check is whether or not the computed oscillator strength is exactly 0, which it should be for n-pi* for D2h in something like D2h p-quinone, or tetra-aza benzene or naphthalene, for example. Cheers! John McKelvey On Fri, Aug 22, 2008 at 4:52 AM, Matthew K Morantz matthew.morantz{} gmail.com wrote: > > Sent to CCL by: "Matthew K Morantz" [matthew.morantz-.-gmail.com] > Hi, > > Just a quick and simple question: > > I've optimized a D2h-symmetry molecule at the DFT-B3LYP-6/31G level of > theory in Gaussian. I've figured out the HOMO-LUMO gap from the orbital > energies. > I'm now attempting to correlate this gap with the experimental max of the > molecule. > I know that E(HOMO-LUMO) = E(lambdamax) = hv and have calculated > E(max)experimental and E(lambdamax)theoretical as a result. > > However, E(lambdamax)exp > E(lambdamax)theo and I want to check whether > solvation effects could be expected to cause a red- or blue-shift. For this, > I need to know whether the b1g --> b3u transition at max is n-->pi* or > pi-->pi*. > > How do I go about figuring that out from my calculations? > > Thanks, > > Matthew Morantz > matthew.morantz:+:gmail.com> > > ------=_Part_36727_18474373.1219422391207 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Content-Disposition: inline
One immediate check is whether or not the computed oscillator strength is exactly 0, which it should be for n-pi* for D2h in something like D2h p-quinone, or tetra-aza benzene or naphthalene, for example.

Cheers!

John McKelvey

On Fri, Aug 22, 2008 at 4:52 AM, Matthew K Morantz matthew.morantz{}gmail.com <owner-chemistry||ccl.net> wrote:

Sent to CCL by: "Matthew K Morantz" [matthew.morantz-.-gmail.com]
Hi,

Just a quick and simple question:

I've optimized a D2h-symmetry molecule at the DFT-B3LYP-6/31G level of theory in Gaussian. I've figured out the HOMO-LUMO gap from the orbital energies.
I'm now attempting to correlate this gap with the experimental max of the molecule.
I know that E(HOMO-LUMO) = E(lambdamax) = hv and have calculated E(max)experimental and E(lambdamax)theoretical as a result.

However, E(lambdamax)exp > E(lambdamax)theo and I want to check whether solvation effects could be expected to cause a red- or blue-shift. For this, I need to know whether the b1g --> b3u transition at max is n-->pi* or pi-->pi*.

How do I go about figuring that out from my calculations?

Thanks,

Matthew Morantz
matthew.morantz:+:gmail.com



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