Predicting IR Absorbance Peaks: C4v Point Group

[CrimpJiggler]

Lets say I need to predict the number of infrared absorbance peaks that will appear on the IR spectrum of a given molecule. As an example, I'll use this molecule:

I can see that the point group of this molecule is C_4v. I can look up this point groups character table:
http://img685.imageshack.us/img685/7360/charactertb.png
I'll be honest, I have no idea what this character table actually means but from what I remember, it tells me how many IR and raman absorbances the molecule has. If I'm not mistaken, the table says this molecule has 2 IR absorbances and 2 raman absorbances. How do I find out which of these are IR or raman active? In the past, I came across 2 methods involving irreducible representations and other stuff that I don't understand and I couldn't get either method to work. How do YOU do this? I'm looking for a good, solid algorithm that I can use to solve this problem for the majority of molecules that I come across.

 

[jbsteele]

The most reliable and comprehensive method to predict the number of infrared absorbance peaks that will appear on the IR spectrum of a given molecule is to use vibrational spectral analysis software such as Gaussian, HyperChem, or GaussView. This type of software will generate an IR spectrum of the molecule based on its structure, and then you can compare it to the point group character table to determine which peaks are IR active and which are not. This method is the most accurate and will allow you to accurately predict the number of IR absorbance peaks for any given molecule.