IR NU-S(XH) ABSORPTION-BAND SHAPE IN H-BONDED COMPLEX .1. THEORY

The IR band shape theory of the stretching mode νs (XH...Y) in H-bonded complexes is presented. The proton in the H-bond involves motion in the Born-Oppenheimer energy potential which is accompanied by the anharmonic coupling to the low-frequency hydrogen-bridge stretching motion νσ. Both the energy potential well and the anharmonic coupling are randomly modulated with time. The fluctuations of the energy potential arising from the direct coupling to the bath obey the stochastic Liouville equation. The time evolution of the anharmonic coupling constant is governed by the resonance energy exchange between the νσ mode and the bath. The theory can be applied both to weak and strong H-bonds. © 1990.