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 !!
 	Sergiusz Kwasniewski
 	Universitaire Campus Gebouw D
 	3590 Diepenbeek
 	tel(direct): 032 (0)11/268315
 	fax	   : 032 (0)11/268301
 	email      : sergiusz.kwasniewski.,at,