Nonadiabatic rotational excitation of benzene by nonresonant intense femtosecond laser fields

We investigated the nonadiabatic rotational excitation of the oblate symmetric-top molecule, benzene, induced by nonresonant intense ultrashort laser fields. By employing a quantum-state resolved probe using ns laser pulses, rotational excitation up to J = 10 was observed for the irradiation of a molecular ensemble, initially cooled to 0.5 K in an adiabatic expansion, by the femtosecond laser pulse with the intensity of 2.2 TW/cm2. The observed excitation was analyzed by the aid of quantum mechanical calculations. These calculations show the systematic change in the excitation pathways for different K, which is characteristic of nonadiabatic rotational excitation in symmetric-top molecules.