Homework 5

I would like to give you practice in seeing exactly how the theory of spectral bandshapes that we talked about in class works. I have written a program (a long time ago, it is a DOS program!) that predicts spectral bandshapes using the theories and equations that we talked about in class. Remember that the band shape is determined by the energy of the excited state (DeltaE0,0), the solvent reorganization energy (lambdas), the vibrational reorganization energy (lambdav), and the vibrational frequency( nuv), etc.

The program allows you to load real spectra, and then to play with the parameters (manually) to see which values best reproduce the spectra. You will find that the fitting procedure will not necessarily give only one set of parameters, but it isn't too bad. More importantly, the process of doing the fitting will allow you to "see" what the parameters actually "do".

The program is called "SS5" and it is on the Chem Users web server. You can also download the program file directly by clicking HERE.

You will need to download several spectrum files to simulate, these are given below. The spectra are for 9,10-dicyanoanthracene in two different solvents, the non-polar cyclohexane abd the polar acetionitrile. Your job will be to find the best values of the parameters that best reproduce the experimental spectra.

You should not expect to get a perfect fit, since the theory contains several approximations. You will almost certainly have to use more than one vibrational frequency (the program has provision for up to three). You should expect to fit the emission spectra better than the absorption spectrum, since only one state emits, whereas there may be overlapping absorption spectra.

PROCEDURES: The program and the data files need to be in the same folder, I suggest simply using the Desktop. To run the program, just double click on its icon. Because it is an old DOS program, I don't think that you will be able to print your spectra. So, just write down the best parameters, and hand that in to me.

Here are the spectrum files
DCA in acetonitrile absorption spectrum, acnabs.txt
DCA in cyclohexane absorption spectrum, chxabs.txt
DCA in acetonitrile emission spectrum, acnem.txt
DCA in cyclohexane emission spectrum, chxem.txt

Here is the program file
SS5