Noise-induced dynamic symmetry breaking and stochastic transitions in ABA molecules: II. Symmetric–antisymmetric normal mode switching

The second paper of the series discusses the effect of thermal noise on the stretching vibrational dynamics of symmetric triatomic ABA molecules. In particular, noise-induced transitions between symmetric and antisymmetric normal-mode vibrations are discussed, in the context of symmetry breaking of vibrational dynamics. The statistics of symmetry breaking transitions and the average lifetimes of normal modes of different symmetries are derived analytically and compared with direct numerical simulations. The average lifetimes of symmetric and antisymmetric normal modes are found to be inversely proportional to bath friction strength and depend on the dimensionless parameter j which is the combination of bath temperature, bond anharmonicity and bond–bond coupling strength. Antisymmetric normal mode depends weakly on j and is always stable. Symmetric normal mode depends significantly on j and becomes unstable at j 1⁄4 1. Higher temperatures destabilize symmetric normal mode and therefore decrease the ratio of symmetric-to-antisymmetric normal mode populations contrary to intuitive expectation. 2010 Elsevier B.V. All rights reserved.