DYNAMICAL TUNNELING THROUGH A CHAOTIC REGION - A CONTINUOUSLY DRIVEN RIGID ROTOR

It is shown that a non-vibrating diatomic molecule (i.e. a rigid rotor ) in the presence of a strong laser field changes its hindered rotatio nal motion (which on the average is in resonance with the oscillating time dependent field) from anti-clockwise to clockwise (hindered) rota tional motion. This transition is classically forbidden and is another example of a quantum mechanical tunneling phenomenon occurring due to the time-reversal symmetry of the Hamiltonian. Classically, the two s table rotational modes are separated by an extended chaotic region in phase space. The Husimi representation of the quasienergy states of th e time-periodic quantum system enables us to localize wave packets ins ide the classical stability islands. The effect of the field and the m olecular parameters on the period of this oscillation is obtained from the quasienergy splittings without the need to carry out long time de pendent computations. An analytical analysis of the dynamical tunnelin g using an extended version of the (t, t') formalism recently develope d (J. Chem. Phys. 99, 4590 (1993)) is in remarkable agreement with the numerical results.