Anomalous Λ-Doubling in the Infrared Spectrum of the Hydroxyl Radical in Helium Nanodroplets

Liang, Tao; Douberly, Gary E.

doi:10.1021/jp312335q

Cited by 28 publications

(31 citation statements)

References 42 publications

(80 reference statements)

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“…(2)]. We would like to point out that since the experiments on HCl [94] and OH [96] did not detect any significant renormalization of the rotational constant, the corresponding experimental values of B Ã =B were set to 1. While our theory indeed predicts B Ã =B ≈ 1 for the case of OH, we observe B Ã =B ≈ 0.98 for HCl, which is quite close to the corresponding value for HF.…”

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confidence: 99%

A New Angle on Quantum Impurities

Shchadilova

2017

Physics

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Understanding the behavior of molecules interacting with superfluid helium represents a formidable challenge and, in general, requires approaches relying on large-scale numerical simulations. Here, we demonstrate that experimental data collected over the last 20 years provide evidence that molecules immersed in superfluid helium form recently predicted angulon quasiparticles [Phys. Rev. Lett. 114, 203001 (2015)]. Most important, casting the many-body problem in terms of angulons amounts to a drastic simplification and yields effective molecular moments of inertia as straightforward analytic solutions of a simple microscopic Hamiltonian. The outcome of the angulon theory is in good agreement with experiment for a broad range of molecular impurities, from heavy to medium-mass to light species. These results pave the way to understanding molecular rotation in liquid and crystalline phases in terms of the angulon quasiparticle. DOI: 10.1103/PhysRevLett.118.095301 Among its many peculiar properties, superfluid 4 He is quite averse to mixing with impurities which could serve as a microscopic probe of the superfluid phase. As a result, for several decades after the discovery of superfluidity by Allen, Misener, and Kapitza [1,2], only macroscopichydrodynamic-properties of superfluid helium have been studied in the laboratory. In the 1990s, however, it was demonstrated that atoms and molecules can be trapped in superfluid helium if the latter forms little droplets containing on the order of 1000 helium atoms [3][4][5][6][7]. Over the following years, trapping atoms, molecules, and ions inside superfluid helium nanodropletssometimes called "nanocryostats"-emerged as an important tool of molecular spectroscopy [6][7][8][9][10][11][12]. Such nanodroplets allow us to trap single molecules in a cold environment (∼0.4 Kelvin), thereby isolating them from external perturbations. This allows us to record spectra free of collisional and Doppler broadening, as well as to study species that are unstable in the gas phase, such as free radicals.While superfluid helium does not cause a substantial broadening of molecular spectral lines, it affects molecular rotation. In particular, molecules in superfluid helium nanodroplets acquire an effective moment of inertia that is larger compared to its gas-phase value [6,9]. The relative magnitude of the effect increases from lighter to heavier species and is somewhat similar to renormalization of the effective mass for electrons interacting with a crystalline lattice [13][14][15][16].Semiclassically, molecular rotation in helium can be rationalized within the "adiabatic following" model [6,7,[17][18][19][20][21][22]. There, it is assumed that the molecule induces a local density deformation (a "nonsuperfluid shell") of helium which corotates along with the molecule, thereby increasing its moment of inertia. However, such a classical approach does not allow us to get insight into the intriguing aspects of the problem arising from quantum many-body physics. Helium, on the other hand, repres...

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confidence: 99%

A New Angle on Quantum Impurities

Shchadilova

2017

Physics

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“…The droplet expansion is skimmed into a beam and passes into a chamber containing the source of hydroxyl radicals. The OH radicals are produced via the pyrolytic decomposition of tert-butyl hydroperoxide, as described previously [10,31,34]. The helium droplets ''pick-up'' OH radicals as they emanate from this effusive pyrolysis source, and the internal degrees of freedom of the radical are cooled to less than 0.4 K via He atom evaporation [31].…”

Section: Experimental Methodsmentioning

confidence: 99%

“…The OH radicals are produced via the pyrolytic decomposition of tert-butyl hydroperoxide, as described previously [10,31,34]. The helium droplets ''pick-up'' OH radicals as they emanate from this effusive pyrolysis source, and the internal degrees of freedom of the radical are cooled to less than 0.4 K via He atom evaporation [31]. Downstream from the OH pick-up zone, the OH doped droplet beam passes through a 2 cm long differentially pumped gas cell that contains %10 À6 Torr of either C 2 H 2 , C 2 H 4 , or H 2 O.…”

Section: Experimental Methodsmentioning

confidence: 99%

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On the Stark effect in open shell complexes exhibiting partially quenched electronic angular momentum: Infrared laser Stark spectroscopy of OH–C2H2, OH–C2H4, and OH–H2O

Moradi

Douberly

2015

Journal of Molecular Spectroscopy

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a b s t r a c tThe Stark effect is considered for polyatomic open shell complexes that exhibit partially quenched electronic angular momentum. Matrix elements of the Stark Hamiltonian represented in a parity conserving Hund's case (a) basis are derived for the most general case, in which the permanent dipole moment has projections on all three inertial axes of the system. Transition intensities are derived, again for the most general case, in which the laser polarization has projections onto axes parallel and perpendicular to the Stark electric field, and the transition dipole moment vector is projected onto all three inertial axes in the molecular frame. Simulations derived from this model are compared to experimental rovibrational Stark spectra of OH-C 2 H 2 , OH-C 2 H 4 , and OH-H 2 O complexes formed in helium nanodroplets.

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“…Recent advances in infrared spectroscopic techniques of helium nanodroplets allow measurement of rovibrational spectra of many transient species, including fragile molecules, [84] unstable isomers, [85][86][87] ions, [88] and radicals. [84,89,90] It is of interest to extract superfluid information from those spectra through theoretical simulations. The open-shell or multireference nature of the transient species can cause additional difficulties for the calculation of their interactions with a He atom.…”

Section: Future Prospectsmentioning

confidence: 99%

Potential generation and path‐integral Monte Carlo in study of microscopic superfluidity

Zeng

Roy

2014

Int J of Quantum Chemistry

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The idea of a macroscopic Andronikashvili experiment used to measure superfluid fraction of bulk liquid 4 He can be ported into the realm of spectroscopic studies to measure the superfluid fraction of microscopic systems at the nanoscale. Theoretical studies are needed to fully unravel the superfluid information contained in such a microscopic Andronikashvili experiment. Two aspects of the theoretical studies, the generation of accurate and efficient potential energy surfaces, and the methodology of path-integral Monte Carlo simulations are briefly introduced in this article.

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Anomalous Λ-Doubling in the Infrared Spectrum of the Hydroxyl Radical in Helium Nanodroplets

Cited by 28 publications

References 42 publications

A New Angle on Quantum Impurities

A New Angle on Quantum Impurities

On the Stark effect in open shell complexes exhibiting partially quenched electronic angular momentum: Infrared laser Stark spectroscopy of OH–C2H2, OH–C2H4, and OH–H2O

Potential generation and path‐integral Monte Carlo in study of microscopic superfluidity

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