Formation of coherent rotational wavepackets in small molecule-helium clusters using impulsive alignment

Abstract

We show that rotational line spectra of molecular clusters with near zero permanent dipole moments can be observed using impulsive alignment. Aligned rotational wavepackets were generated by non-resonant interaction with intense femtosecond laser pump pulses and then probed using Coulomb explosion by a second, time-delayed femtosecond laser pulse. By means of a Fourier transform a rich spectrum of rotational eigenstates was derived. For the smallest cluster, C 2 H 2 -He, we were able to establish essentially all rotational eigenstates up to the dissociation threshold on the basis of theoretical level predictions. The C 2 H 2 -He complex is found to exhibit distinct features of large amplitude motion and very early onset of free internal rotor energy level structure.

Disruptive photon technologies for chemical dynamics

“…35 Laser-induced alignment of gas molecules 2 can also be categorised as a sample delivery and preparation technique, even though the study of rotational dynamics of complex systems is itself a vibrant eld of chemical dynamics. 80 Laser alignment is improved by cooling the molecules to a rotational temperature of about 1 K and selecting low-energy quantum states using an electrostatic deector, as was used for initial experiments of diffractive imaging of aligned diiodobenzonitrile molecules. 38 Most chemical reactions are not accessible via initiation of a laser pulse or temperature jump.…”

“…Gas cells provide fresh sample by diffusion and can give a longer interaction length with the X-ray beam, to give higher signals, but this can complicate the scattering geometry 35 . Laser-induced alignment of gas molecules 2 can also be categorised as a sample delivery and preparation technique, even though the study of rotational dynamics of complex systems is itself a vibrant field of chemical dynamics 80 . Laser alignment is improved by cooling the molecules to a rotational temperature of about 1 K and selecting low-energy quantum states using an electrostatic deflector, as was used for initial experiments of diffractive imaging of aligned diiodobenzonitrile molecules 38 .…”

Impulsive alignment of 4He–CH3I: A theoretical study

“…Along this line, more recent studies are focusing on the alignment of molecules that interact with one another, weakly bound molecular systems involving van der Waals bonds, or molecules coupled to an environment in the solid or liquid phase. [14][15][16][17][18][19][20][21] Laser induced alignment of molecules in a liquid is hindered by several mechanisms which are absent in vacuum. In a classical solvent, molecular rotation is not free due to the molecular forces exerted by the surrounding environment.…”

Emerging photon technologies for chemical dynamics

“…[33][34][35] The range of systems, scientic problems, sources and methods that all these emerging technologies are covering is impressive and this issue is a perfect snapshot of the state-of-the-art. In terms of systems, papers are presented which concern isolated gas phase molecules, 31,32,[36][37][38][39][40][41] clusters, 42 metal complexes, 30,43,44 quantum dots, 45 biosystems, 31,[46][47][48][49] surfaces/interfaces, [43][44][45] Mott-Peierls insulators, 33 superconductors, 34 ionic crystals, 50 and graphene. 35 These deal with scientic issues such as the structural dynamics of molecules, 30,32,[36][37][38][39]41 the charge and spin dynamics in molecules, 30,31,37,38 solvation dynamics, 30,46 surface and interface phenomena, [43][44][45] charge density waves, magnetism and melting in materials.…”