Interaction-induced absorption the characteristics

We have seen that supermolecular spectra differ from the spectra of single atoms or molecules in a variety of ways which we briefly summarize. 

If both AEa and A b equal zero, we have a purely translational line of the supermolecule. These can be found at frequencies comparable to the width Av, that is in the microwave and far-infrared regions of the spectrum. 

If just one of the A a, A b is non-zero, collision-induced rotovibra-tional or electronic bands occur whose line centers coincide with a transition frequency of one of the molecules. 

Induced spectra may appear at frequencies corresponding to molecular transitions that may be allowed or forbidden in the isolated molecules. Induced spectra associated with allowed transitions can sometimes be studied but this is not always easy in the presence of strong, allowed lines. Induced spectra of forbidden transitions (A = 0 in Eq. 1.2), on the other hand, are quite common and are generally easy to recognize. 

Induced lines have also been seen at frequencies given by sums and differences of transition frequencies of the molecules involved. These 

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