The effect of light-induced conical intersections on the alignment of diatomic molecules

Abstract

It has already been shown that dressing of diatomic molecules by standing or by running linearly polarized laser waves gives rise to conical intersections (CIs). Due to the presence of such light-induced CIs (LICI), the rovibronic molecular motions are strongly coupled. Here we investigate an impact of LICI on molecular alignment. We show that the degree of alignment of a diatomic molecule as a function of time as obtained from the rigid rotor calculations (where the LICI is ignored) is very different from the exact calculations (where the LICI is taken into consideration). This claim is valid under an assumption that the initially prepared wavepacket has a significant amplitude at the nuclear geometry where the LICI is located. Moreover, our results clearly show that the LICI increases the electronic excitation of the diatom. In particular for weak laser fields this effect is very significant. Our prediction of the LICI’s effect on the alignment of diatomic molecules can be confirmed by a two-laser experiment. Here, the first laser should have weak intensity and its duration should be sufficiently long as to align the molecules. The wavelength should be tuned in such a way as to ensure that the initial nuclear wavepacket has a significant amplitude at the internuclear distance corresponding to the LICI. The second laser pulse should be strong to produce measurable high-order harmonics. The high-order harmonic generation spectra should be measured as a function of the time delay between the two laser pulses, and are predicted to give an experimental evidence for the LICI effect on the alignment.