Cross-revival of molecular wave packets

We predict that vibration-rotation coupling in diatomic molecules will lead to cross-revivals of vibrational wave packets - provided lifetime effects and collisions can be eliminated. Analytical conditions for full cross-revivals of systems governed by the minimal Hamiltonian exhibiting rotation-vibration coupling are found and the influence of higher-order cross terms is studied. Finally, generality of the phenomenon of molecular cross-revival is investigated by doing numerical calculations for several molecular potentials and temperatures. For expansion-cooled molecules strong cross-revivals are obtained in all cases. In the particular example of cold Li2 in the A 1Σ+u state nearly complete cross-revivals are observed. These cross-revivals survive thermal averaging and reach at an initial temperature of 900 K an amplitude which is close to half the beat amplitude at zero time delay. The rotational cooling mechanism facilitating this, by reducing the effective rotational temperature of the wave packet, is explained in terms of the molecular rotational constants and laser wavelength bandwidth.