Vibrational energy relaxation first term contribution

The first two terms are related to W relaxation and prevail at low vibrational energies the third term is related to VT relaxation and dominates at higher vibrational energies. The linear part of eqrration (3-131), including the first and third terms, is easy to solve, but the second (non-linear) term makes the solution more complicated. It is helpful from this perspective to point out the three cases of strong, intermediate, and weak excitation, corresponding to different levels of contribution from the non-linear term and determined by two dimensionless parameters yy% and... 

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