Quantum entanglement of anharmonic stretches in molecules H2O and SO2 is studied in terms of the reduced-density linear entropy with initial squeezed vacuum states and thermal states. It is shown that the entropy of both kinds of initial states with a small amplitude n̄ is quasi-periodic with the period of thermal states being larger than that of squeezed vacuum states for each molecule. The entropy evolution of both kinds of initial states with a larger amplitude n̄ is irregular. For each kind of initial state, the frequency of oscillation o...
