Intramolecular vibrational dynamical barrier due to extremely irrational couplings

The intramolecular vibrational dynamics due to extremely irrationalcouplings is demonstrated by contrast to the resonance couplings, forthe three-mode case of H$_2$O as an example. The extremelyirrational couplings are shown to impose such strong hindrance tointramolecular vibrational relaxation (IVR) that they act asbarriers. They restrict the direct action/energy transfer between thetwo stretching modes, though they allow the transfer between astretching and a bending modes. In contrast, the resonance is moremediated by the bending mode and leads to chaotic IVR. It is alsoshown that there is a region in the dynamical space in whichresonance and extremely irrational couplings coexist.