Dynamic discrimination of oriented molecules controlled with the nonresonant dynamic Stark effect induced by a single-cycle THz pulse

Abstract

We theoretically propose a control scheme of temporal wave-packet separation for oriented molecules, based on nonresonant dynamic Stark effect (DSE) in the dipole limit. The proposed scheme exploits the fact that diabatic coupling between the lowest two potential-energy curves (PECs) depends on diatomic internuclear distance. In the control process nonresonant DSE shifts the PECs, moves the avoided crossing position, and thus changes transition probability from one PEC to another. In the scheme linearly polarized single-cycle THz pulses are employed as control fields and are applied to the molecules oriented along the field polarization. In this paper the proposed scheme is applied to the temporal wave-packet separation of the binary mixture of alkali-halide isotopologues $^{133}\mathrm{CsI}$ and $^{135}\mathrm{CsI}$. We assume that before applying the control pulse one of the isotopologues is oriented along the field polarization direction and the other is oriented along the opposite direction (isotope-dependent orientation) and then they are electronically excited from the ground-state PEC to the excited-state counterpart. Numerical wave-packet propagations under some control pulses reveal that a THz pulse yields a temporal wave-packet separation of about 2 ps between the two isotopologue photodissociations. We also consider the cases where the molecular axis is not parallel to the field polarization direction and carry out the same wave-packet calculations. It is found, as a result, that the temporal wave-packet separation is comparable with the parallel case, indicating that even when the isotope-dependent orientation right before control is not perfectly achieved, the proposed control scheme works well. This result suggests that the present separation scheme for oriented molecules is more robust against imperfect orientation than the molecular separation technique using the dependence of electronic transition probability on the field polarization direction relative to the molecular axis.