Resonant collisionless dissociation in interaction between a high-intensity harmonic field and two coupled anharmonic molecular modes

An analysis is made of a mechanism of resonant excitation of one of two coupled anharmonic molecular modes for which the sum frequency allowing for the energy dependence of the frequencies is maintained close to the frequency of the external field as a result of automatic phase stabilization caused by interaction between a nonlinear vibrational system and the harmonic external field. If the system of molecular modes is dissipative, the energy of one of the modes increases (whilst that of the other mode decreases accordingly) during establishment of equilibrium when the sum of the mode frequencies is kept constant. The possibility of the sum of the vibration frequencies of two molecular modes being kept constant during the total excitation process is substantiated analytically and numerically for parameters typical of real molecules and fields. An analysis is made of changes in energy during the interaction process. It is found that a mode having its energy initially higher than that of the coupled mode may be excited and during the excitation process, the strongest bond may be broken.