We simulate the non-adiabatic laser alignment of the weakly bound 4He-CH3I complex based on a quantum mechanical wave packet calculation for a model He-CH3I interaction potential. Two different regimes are found depending on the laser intensity. At intensities typical of non-adiabatic alignment experiments, the rotational dynamics resembles that of the isolated molecule. This is attributed to the fact that after the initial prompt alignment peak the complex rapidly dissociates. The subsequent revival pattern is due to the free rotation of the molecule detached from the helium atom. It is superimposed to a flat background corresponding to ∼20% of the wave packet which remains bound, containing lower rotational excitation. At lower intensities, dissociation is avoided but the rotational excitation is not high enough to provide an efficient alignment and a broad non-regular structure is observed. Besides, the interaction of the He atom with the molecule quenches any possible alignment. These interpretations are based on the calculation of different observables related to the rotational motion. We compare our findings with recent experimental and theoretical results of non-adiabatic alignment of linear molecules solvated in helium nanodroplets or weakly interacting with one helium atom.

Synopsis We present a quantum dynamical analysis of the adiabatic alignment and subsequent rotational motion of the CH3IHe complex, excited by strong off-resonant laser pulses. In this context, the emphasis is laid on the effect of the helium atom onto the coherent time evolution of the rotor states. The results are discussed with respect to experiments of adiabatic alignment in superfluid He droplets where a strong decoherence of the rotor states was observed.

The dynamics of small molecules and their charged photofragments inside helium (He) nanodroplets following photoexcitation into dissociative states and ionization is a field of particular interest (see e.g. [1] and references therein). These studies aim at facilitating the understanding of charge transfer reactions inside He nanodroplets which are likely to be drastically affected by processes such as redistribution of He solvation shells. Besides, the escape process of both electrons and ions from the droplet is not well understood yet.