Density of states of helium droplets

Hansen, Klavs; Johnson, Michael D.; Kresin, Vladimir Z.

doi:10.1103/physrevb.76.235424

Cited by 9 publications

(7 citation statements)

References 21 publications

(41 reference statements)

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“…The energy gaps associated with all possible rotational relaxation channels are given in Table . For the P Q 1 (1), P R 1 (1), and R R 1 (1) transitions, there is at least one open rotational relaxation channel with an energy difference greater than 18 cm –1 , and because of this, there is essentially a continuous bath of phonon collective droplet modes to which all of these resonances can relax. , These energy gaps are all larger than the maximum energy of an elementary excitation in bulk superfluid 4 He (∼14 cm –1 ) . Therefore, rotational relaxation must occur via the simultaneous excitation of multiple phonons in the liquid.…”

Section: Discussionmentioning

confidence: 99%

“…In the large droplet limit, it is expected that the rate of population decay should be independent of the droplet size, because the density of phonon states increases linearly with the droplet radius, R, 27,28 whereas the coupling matrix element is predicted to scale as R −1/2 . 45 Indeed, we find that the line widths of all five transitions are relatively unchanged in the large droplet limit (N greater than about 8000 atoms).…”

Section: Discussionmentioning

confidence: 99%

“…For relatively “heavy” rotors ( B less than about 0.5 cm –1 ), such as OCS, it is typical for the individual ro-vibrational transitions to be inhomogeneously broadened with full-width at half-maximum (fwhm) line widths between 0.1 to 1 GHz (0.003–0.03 cm –1 ). For these systems, assuming rotational relaxation occurs within the excited vibrational manifold, all possible rotational relaxation channels have energy differences that are in a regime in which the density of phonon states is quite sparse, even for the largest droplet sizes produced in these experiments. − For these heavy rotors, the rotational population relaxation time scale is estimated to be on the order of 10 ns . Moreover, relaxation occurs as a result of the interaction of the dopant with the surface ripplon excitations .…”

Section: Introductionmentioning

confidence: 98%

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Rotational Dynamics of the Methyl Radical in Superfluid ⁴He Nanodroplets

Morrison

Douberly

2012

J. Phys. Chem. A

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We report the ro-vibrational spectrum of the ν3(e') band of the methyl radical (CH3) solvated in superfluid (4)He nanodroplets. Five allowed transitions produce population in the N(K) = 0(0), 1(1), 1(0), 2(2) and 2(0) rotational levels. The observed transitions exhibit variable Lorentzian line shapes, consistent with state specific homogeneous broadening effects. Population relaxation of the 0(0) and 1(1) levels is only allowed through vibrationally inelastic decay channels, and the (P)P1(1) and (R)R0(0) transitions accessing these levels have 4.12(1) and 4.66(1) GHz full-width at half-maximum line widths, respectively. The line widths of the (P)R1(1) and (R)R1(1) transitions are comparatively broader (8.6(1) and 57.0(6) GHz, respectively), consistent with rotational relaxation of the 2(0) and 2(2) levels within the vibrationally excited manifold. The nuclear spin symmetry allowed rotational relaxation channel for the excited 1(0) level has an energy difference similar to those associated with the 2(0) and 2(2) levels. However, the (P)Q1(1) transition that accesses the 1(0) level is 2.3 and 15.1 times narrower than the (P)R1(1) and (R)R1(1) lines, respectively. The relative line widths of these transitions are rationalized in terms of the anisotropy in the He-CH3 potential energy surface, which couples the molecule rotation to the collective modes of the droplet.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 98%

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Rotational Dynamics of the Methyl Radical in Superfluid ⁴He Nanodroplets

Morrison

Douberly

2012

J. Phys. Chem. A

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“…We note that for finite systems, such as helium droplets, other types of excitations can appear. One example are ripplons -quantized surface waves or 'wrinkles' on the droplet surface [50,106]. However, whether one works with molecules in small droplets, bulk helium, or a dilute BEC, many of the properties of the collective excitations are contained in the dispersion relation ω(k).…”

Section: Bogoliubov Approximation and Transformationmentioning

confidence: 99%

CHAPTER 9. Molecular Impurities Interacting with a Many-particle Environment: From Ultracold Gases to Helium Nanodroplets

Lemeshko¹,

Schmidt²

2017

Theoretical and Computational Chemistry Series

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In several settings of physics and chemistry one has to deal with molecules interacting with some kind of an external environment, be it a gas, a solution, or a crystal surface. Understanding molecular processes in the presence of such a many-particle bath is inherently challenging, and usually requires large-scale numerical computations. Here, we present an alternative approach to the problem -that based on the notion of the angulon quasiparticle. We show that molecules rotating inside superfluid helium nanodroplets and Bose-Einstein Condensates form angulons, and therefore can be described by straightforward solutions of a simple microscopic Hamiltonian. Casting the problem in the language of angulons allows not only to tremendously simplify it, but also to gain insights into the origins of the observed phenomena and to make predictions for future experimental studies. A. Second-order perturbation theory 25 B. Nonperturbative analysis in the weak-coupling regime 28 C. The canonical transformation 34 D. The limit of a slowly rotating impurity 35 VI. Conclusions and outlook 37 VII. Acknowledgements 38 A. Angular momentum operators 38 References 41 I. INTRODUCTIONThe properties of polyatomic systems we encounter in physics and chemistry can be extremely challenging to understand. First of all, many of these systems are strongly correlated, in the sense that their complex behavior cannot be easily deduced from the properties of their individual constituents -isolated atoms and molecules. Second,in realistic experiments these systems are usually found far from their thermal equilibrium, as they are perturbed by the surrounding environment, be it a solution, a gas, or lattice vibrations in a crystal. Quite often, however, insight into the behavior of such complex many-body systems can be obtained from studying the simplified problem of a single quantum particle coupled to an environment. These so-called 'impurity problems' represent an important part of modern condensed matter physics [1,2].Interest in quantum impurities goes back to the classic works of Landau, Pekar, Fröhlich, and Feynman, who studied motion of electrons in crystals [3][4][5][6][7][8]. In its most general formulation, such a problem involves the coordinates and momenta of all the electrons and nuclei in the crystal -some 10 23 degrees of freedom -and is therefore intractable by any existing numerical technique. The problem, however, can be drastically simplified by using a trick very common among condensed matter physicists -that of introducing 'quasiparticles.' A quasiparticle is a collective object, whoseproperties are qualitatively similar to those of free particles, however they quantitatively depend on the coupling between the particle and the environment. Fig. 1 shows a few examples of quasiparticles. For example, the behavior of an electron interacting with a crystalline lattice can be understood in terms of a so-called polaron quasiparticle, composed of an electron dressed by a coat of lattice excitations [9,10]. A polaron effectively behav...

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“…Some of these predicted vibrational modes were only confirmed much later [3]. Also the presence of angular momentum in the elementary excitations of helium droplets play a role for their thermal properties, as analyzed in detail in [4].…”

Section: Introductionmentioning

confidence: 98%

Vibrational angular momentum level densities of linear molecules

Hansen,

Ferrari

2020

Preprint

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While linear molecules in their vibrational ground state cannot carry angular momentum around their symmetry axis, the presence of vibrational excitations can induce deformations away from linearity and therefore also allow angular momentum along the molecular axis. In this work, a recurrence relation is established for the calculation of the vibrational level densities (densities of states) of linear molecules, specified with respect to both energy and angular momentum. The relation is applied to the carbon clusters of sizes n = 4, 6, 7 as a case study.

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Density of states of helium droplets

Cited by 9 publications

References 21 publications

Rotational Dynamics of the Methyl Radical in Superfluid ⁴He Nanodroplets

Rotational Dynamics of the Methyl Radical in Superfluid ⁴He Nanodroplets

CHAPTER 9. Molecular Impurities Interacting with a Many-particle Environment: From Ultracold Gases to Helium Nanodroplets

Vibrational angular momentum level densities of linear molecules

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Density of states of helium droplets

Cited by 9 publications

References 21 publications

Rotational Dynamics of the Methyl Radical in Superfluid 4He Nanodroplets

Rotational Dynamics of the Methyl Radical in Superfluid 4He Nanodroplets

CHAPTER 9. Molecular Impurities Interacting with a Many-particle Environment: From Ultracold Gases to Helium Nanodroplets

Vibrational angular momentum level densities of linear molecules

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Rotational Dynamics of the Methyl Radical in Superfluid ⁴He Nanodroplets

Rotational Dynamics of the Methyl Radical in Superfluid ⁴He Nanodroplets