Strongly aligned molecules inside helium droplets in the near-adiabatic regime Journal Article

Author(s): Shepperson, Benjamin; Chatterley, Adam S.; Søndergaard, Anders A; Christiansen, Lars; Lemeshko, Mikhail; Stapelfeldt, Henrik
Article Title: Strongly aligned molecules inside helium droplets in the near-adiabatic regime
Affiliation IST Austria
Abstract: Iodine (I 2 ) molecules embedded in He nanodroplets are aligned by a 160 ps long laser pulse. The highest degree of alignment, occurring at the peak of the pulse and quantified by ⟨cos 2 θ 2D ⟩ , is measured as a function of the laser intensity. The results are well described by ⟨cos 2 θ 2D ⟩ calculated for a gas of isolated molecules each with an effective rotational constant of 0.6 times the gas-phase value, and at a temperature of 0.4 K. Theoretical analysis using the angulon quasiparticle to describe rotating molecules in superfluid helium rationalizes why the alignment mechanism is similar to that of isolated molecules with an effective rotational constant. A major advantage of molecules in He droplets is that their 0.4 K temperature leads to stronger alignment than what can generally be achieved for gas phase molecules -- here demonstrated by a direct comparison of the droplet results to measurements on a ∼ 1 K supersonic beam of isolated molecules. This point is further illustrated for more complex system by measurements on 1,4-diiodobenzene and 1,4-dibromobenzene. For all three molecular species studied the highest values of ⟨cos 2 θ 2D ⟩ achieved in He droplets exceed 0.96.
Keywords: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Other Condensed Matter (cond-mat.other); Atomic Physics (physics.atom-ph); Chemical Physics (physics.chem-ph); Atomic and Molecular Clusters (physics.atm-clus)
Journal Title: The Journal of Chemical Physics
Volume: 147
Issue 1
ISSN: 1089-7690
Publisher: AIP  
Date Published: 2017-06-01
Start Page: Article number: 013946
Sponsor: We acknowledge support from the European Research Council-AdG (Project No. 320459, DropletControl) and the Villum Foundation.
DOI: 10.1063/1.4983703
Open access: yes (repository)