The dissociation of a diatomic molecule in low frequency polychromatic fields of moderate intensities is studied. Genetic Algorithm is invoked to search out a set of four optimal non-resonant frequencies ($\omega_1$ - $\omega_4$), intensities ($\epsilon_1$ - $\epsilon_4$) the and phase angles ($\delta_1 - \delta_4$), for achieving a facile photo dissociation. Time-dependent Hellmann-Feynman theorem is used to gain insight into the frequency resolved energy absorption pattern. The ‘quantum phase space’ structures indicate occurrence of bond breaking dynamics akin to the classical one.

The quantum dynamics of intramolecular H-atom transfer in malonaldehyde is investigated with a model two-dimensional Hamiltonian constructed with the help of available ab initio theoretical data on the relevant portion of the potential energy surface. At zero temperature, the H-atom transfer takes place by tunnelling leading to cis-cis isomerization while the cis-trans channel remains closed. Local excitation of the cis-trans mode by an external field is predicted to quench cis-cis tunnelling isomerization while excitation of the cis-cis mode is found to enhance the isomerization by tunnelling.