From chemistry-request.,at,.server.ccl.net Mon Mar 25 08:55:04 2002 Received: from luc.ac.be ([193.190.2.30]) by server.ccl.net (8.11.6/8.11.0) with ESMTP id g2PDt4p28425 for ; Mon, 25 Mar 2002 08:55:04 -0500 Received: from sbg-ts (localhost [127.0.0.1]) by luc.ac.be (8.9.3/8.9.3) with SMTP id OAA12115 for ; Mon, 25 Mar 2002 14:54:58 +0100 (MET) Date: Mon, 25 Mar 2002 14:54:58 +0100 (MET) Message-Id: <200203251354.OAA12115[ AT ]luc.ac.be> X-Sender: lucp1381 ":at:" mail.luc.ac.be X-Mailer: Windows Eudora Pro Version 2.1.2 Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" To: chemistry ^at^ ccl.net From: sergiusz kwasniewski Subject: question on vibronic coupling calculation Hi everyone, I'm trying to write a program to account for vibronic coupling on UV/Visible absorption spectra. For the vibronic progression with only one symmetric vibrational mode and up to 3 quanta, the Frank-Condon approximation is fairly easy to implement. However, if I want to include more vibrational modes, I encounter a small problem: I(lambda) ~ SUM ( PRODUCT ( F.C.'s) * D ) where lambda is given in wavelength (nm), the sum is over the quanta (0-3), and the product over the Frank-Condon factors corresponding to the different vibrational modes. Now: in order to describe the band shape factor D, I have to calculate a factor (lambda - lambda(max))^2. How does this factor change while including more than one vibrational frequency ? What I found is: (lambda - (lambda(max) + SUM nu * omega))^2 where nu is the quantum (which is a constant in this summation) and omega is the energy of the vibration, but then instead of having a series of 6 additional peaks besides your lambda(max) (i.e. 3 per vibrational modes), these modes are coupled now 2 by 2 in order to give 3 additional peaks but with an almost doubled spacing (depending on the energies of the vibrations off course). Does anyone know if this is correct, the literature I found about vibronic coupling doesn't explain this thoroughly. I appreciate any kind of help !! Serge ___________________________________________________ Sergiusz Kwasniewski LUC SBG/TS Universitaire Campus Gebouw D 3590 Diepenbeek BELGIUM tel(direct): 032 (0)11/268315 fax : 032 (0)11/268301 email : sergiusz.kwasniewski[ AT ]luc.ac.be http://www.luc.ac.be/Research/TheoChem ___________________________________________________