Hidden-crossing mechanism of rotational excitation of H2O by electric pulse

Rotational excitation of the water molecule by an electric pulse F(t) of Gaussian shape is studied in the framework of the adiabatic approach. The hidden crossings between rotational energy surfaces of H2O in the complex F-plane are calculated by describing H2O as an asymmetric-top rotor with electric dipole moment. It is found that the probabilities of the transitions oscillate uniformly with respect to the length of the pulse due to the interference between elementary transitions via hidden crossings during increasing and decreasing stages of the pulse. For a long pulse, the transition probabilities obtained in the adiabatic approximation are in good agreement with the exact numerical results: the longer the pulse the better the agreement