@article{11552, abstract = {Rotational dynamics of D2 molecules inside helium nanodroplets is induced by a moderately intense femtosecond pump pulse and measured as a function of time by recording the yield of HeD+ ions, created through strong-field dissociative ionization with a delayed femtosecond probe pulse. The yield oscillates with a period of 185 fs, reflecting field-free rotational wave packet dynamics, and the oscillation persists for more than 500 periods. Within the experimental uncertainty, the rotational constant BHe of the in-droplet D2 molecule, determined by Fourier analysis, is the same as Bgas for an isolated D2 molecule. Our observations show that the D2 molecules inside helium nanodroplets essentially rotate as free D2 molecules.}, author = {Qiang, Junjie and Zhou, Lianrong and Lu, Peifen and Lin, Kang and Ma, Yongzhe and Pan, Shengzhe and Lu, Chenxu and Jiang, Wenyu and Sun, Fenghao and Zhang, Wenbin and Li, Hui and Gong, Xiaochun and Averbukh, Ilya Sh and Prior, Yehiam and Schouder, Constant A. and Stapelfeldt, Henrik and Cherepanov, Igor and Lemeshko, Mikhail and Jäger, Wolfgang and Wu, Jian}, issn = {10797114}, journal = {Physical Review Letters}, number = {24}, publisher = {American Physical Society}, title = {{Femtosecond rotational dynamics of D2 molecules in superfluid helium nanodroplets}}, doi = {10.1103/PhysRevLett.128.243201}, volume = {128}, year = {2022}, } @article{11998, abstract = {Recently it became possible to study highly excited rotational states of molecules in superfluid helium through nonadiabatic alignment experiments (Cherepanov et al 2021 Phys. Rev. A 104 L061303). This calls for theoretical approaches that go beyond explaining renormalized values of molecular spectroscopic constants, which suffices when only the lowest few rotational states are involved. As the first step in this direction, here we present a basic quantum mechanical model describing highly excited rotational states of molecules in superfluid helium nanodroplets. We show that a linear molecule immersed in a superfluid can be seen as an effective symmetric top, similar to the rotational structure of radicals, such as OH or NO, but with the angular momentum of the superfluid playing the role of the electronic angular momentum in free molecules. The simple theory sheds light onto what happens when the rotational angular momentum of the molecule increases beyond the lowest excited states accessible by infrared spectroscopy. In addition, the model allows to estimate the effective rotational and centrifugal distortion constants for a broad range of species and to explain the crossover between light and heavy molecules in superfluid 4He in terms of the many-body wavefunction structure. Some of the above mentioned insights can be acquired by analyzing a simple 2 × 2 matrix.}, author = {Cherepanov, Igor and Bighin, Giacomo and Schouder, Constant A. and Chatterley, Adam S. and Stapelfeldt, Henrik and Lemeshko, Mikhail}, issn = {1367-2630}, journal = {New Journal of Physics}, number = {7}, publisher = {IOP}, title = {{A simple model for high rotational excitations of molecules in a superfluid}}, doi = {10.1088/1367-2630/ac8113}, volume = {24}, year = {2022}, } @article{10631, abstract = {We combine experimental and theoretical approaches to explore excited rotational states of molecules embedded in helium nanodroplets using CS2 and I2 as examples. Laser-induced nonadiabatic molecular alignment is employed to measure spectral lines for rotational states extending beyond those initially populated at the 0.37 K droplet temperature. We construct a simple quantum-mechanical model, based on a linear rotor coupled to a single-mode bosonic bath, to determine the rotational energy structure in its entirety. The calculated and measured spectral lines are in good agreement. We show that the effect of the surrounding superfluid on molecular rotation can be rationalized by a single quantity, the angular momentum, transferred from the molecule to the droplet.}, author = {Cherepanov, Igor and Bighin, Giacomo and Schouder, Constant A. and Chatterley, Adam S. and Albrechtsen, Simon H. and Muñoz, Alberto Viñas and Christiansen, Lars and Stapelfeldt, Henrik and Lemeshko, Mikhail}, issn = {2469-9934}, journal = {Physical Review A}, number = {6}, publisher = {American Physical Society}, title = {{Excited rotational states of molecules in a superfluid}}, doi = {10.1103/PhysRevA.104.L061303}, volume = {104}, year = {2021}, } @article{8170, abstract = {Alignment of OCS, CS2, and I2 molecules embedded in helium nanodroplets is measured as a function of time following rotational excitation by a nonresonant, comparatively weak ps laser pulse. The distinct peaks in the power spectra, obtained by Fourier analysis, are used to determine the rotational, B, and centrifugal distortion, D, constants. For OCS, B and D match the values known from IR spectroscopy. For CS2 and I2, they are the first experimental results reported. The alignment dynamics calculated from the gas-phase rotational Schrödinger equation, using the experimental in-droplet B and D values, agree in detail with the measurement for all three molecules. The rotational spectroscopy technique for molecules in helium droplets introduced here should apply to a range of molecules and complexes.}, author = {Chatterley, Adam S. and Christiansen, Lars and Schouder, Constant A. and Jørgensen, Anders V. and Shepperson, Benjamin and Cherepanov, Igor and Bighin, Giacomo and Zillich, Robert E. and Lemeshko, Mikhail and Stapelfeldt, Henrik}, issn = {10797114}, journal = {Physical Review Letters}, number = {1}, publisher = {American Physical Society}, title = {{Rotational coherence spectroscopy of molecules in Helium nanodroplets: Reconciling the time and the frequency domains}}, doi = {10.1103/PhysRevLett.125.013001}, volume = {125}, year = {2020}, } @article{994, abstract = {The formation of vortices is usually considered to be the main mechanism of angular momentum disposal in superfluids. Recently, it was predicted that a superfluid can acquire angular momentum via an alternative, microscopic route -- namely, through interaction with rotating impurities, forming so-called `angulon quasiparticles' [Phys. Rev. Lett. 114, 203001 (2015)]. The angulon instabilities correspond to transfer of a small number of angular momentum quanta from the impurity to the superfluid, as opposed to vortex instabilities, where angular momentum is quantized in units of ℏ per atom. Furthermore, since conventional impurities (such as molecules) represent three-dimensional (3D) rotors, the angular momentum transferred is intrinsically 3D as well, as opposed to a merely planar rotation which is inherent to vortices. Herein we show that the angulon theory can explain the anomalous broadening of the spectroscopic lines observed for CH 3 and NH 3 molecules in superfluid helium nanodroplets, thereby providing a fingerprint of the emerging angulon instabilities in experiment.}, author = {Cherepanov, Igor and Lemeshko, Mikhail}, journal = {Physical Review Materials}, number = {3}, publisher = {American Physical Society}, title = {{Fingerprints of angulon instabilities in the spectra of matrix-isolated molecules}}, doi = {10.1103/PhysRevMaterials.1.035602}, volume = {1}, year = {2017}, }