Vibrational Spectroscopy with Neutrons

Mitchell, Peter; Parker, Stewart F.; Ramirez‐Cuesta, Anibal J.; Tomkinson, J.

doi:10.1142/5628

Cited by 329 publications

(280 citation statements)

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“…We also note that, from the outset, this spectral feature exhibits prominent recoil associated with the entire H2 molecule. This behaviour seems to violate the well-known Sachs-Teller tensor mass theory [16], which would classically predict an m = 4/3 amu recoil, instead of the observed m = 2 amu. This can be explained on the basis of the characteristic and quite disparate energy scales of centre-of-mass H2 motions in the solid and liquid phases (about 5 meV) relative to the quantum H2 rotations and the intramolecular H-H motions (516 meV, the highest-known vibrational energy of a fundamental in condensed matter).…”

Section: Solid and Liquid H2mentioning

confidence: 54%

“…The data consists of a series of apparent steps originating at zero energy transfer, in addition there is a continuous sweep of intensity originating at ~500 meV. When a light particle is struck by a neutron it recoils with an energy, Etotal (meV), given by [4,8]:…”

Section: Solid and Liquid H2mentioning

confidence: 99%

“…This has been done with either a phenomenological model of how the rotational energy levels behave in an applied potential [4] or have required very sophisticated multi-dimensional ab initio calculations [7]. These difficulties could be reduced by studying the fundamental H-H stretch vibration at 516 meV, because the calculation is now a conventional lattice dynamics problem, which is tractable with density functional theory [8].…”

Section: Introductionmentioning

confidence: 99%

“…These studies are almost invariably carried out with the J 01 rotational line at 14.5 meV of parahydrogen as the probe of choice [4]. The reasons for this are that not only its transition energy [4] but also its underlying line shape [5,6] are sensitive probes of the local environment and the instruments generally have their best resolution in this energy region.…”

Section: Introductionmentioning

confidence: 99%

“…Inelastic neutron scattering (INS) is well-suited to studies of such systems because the large 1 H cross section and the transparency of most materials to neutrons means that most of the information obtained directly relates to the adsorbed dihydrogen. These studies are almost invariably carried out with the J 01 rotational line at 14.5 meV of parahydrogen as the probe of choice [4]. The reasons for this are that not only its transition energy [4] but also its underlying line shape [5,6] are sensitive probes of the local environment and the instruments generally have their best resolution in this energy region.…”

mentioning

confidence: 99%

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Observation of the stretch mode in H₂ and D₂ by inelastic neutron scattering spectroscopy

Parker

Ewings

Fernandez-Alonso

et al. 2018

J. Phys.: Conf. Ser.

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Abstract. The interaction of H2 with materials is relevant to areas such as catalysis, hydrogen storage and fuel cells. Inelastic neutron scattering has been extensively used for such studies, which have generally utilised the J 01 rotational line at 14.5 meV of parahydrogen. Unfortunately, this is very difficult to model. The problem would be mitigated by studying the fundamental H-H stretch vibration at 516 meV, because the calculation becomes a conventional lattice dynamics problem, which is tractable with density functional theory. Here, we have chosen to investigate solid and liquid H2 and D2 as a test of whether it is possible to observe the H-H and D-D stretch. This is only possible with a direct geometry spectrometer at a spallation neutron source, since only this combination of facilities gives access to high energy neutrons with a wide range of momentum transfer. The measurements were successful and, in addition to several rotational states of the ground vibrational state, a feature recoiling from an origin value of 516 meV for H2 and from 370 meV for D2 is observed in both the solid and liquid states. These are assigned to the H-H and D-D stretch respectively. IntroductionThe study of molecular hydrogen (H2, dihydrogen) in, or on, materials is relevant to areas such as catalysis [1], hydrogen storage [2] and fuel cells [3]. Inelastic neutron scattering (INS) is well-suited to studies of such systems because the large 1 H cross section and the transparency of most materials to neutrons means that most of the information obtained directly relates to the adsorbed dihydrogen. These studies are almost invariably carried out with the J 01 rotational line at 14.5 meV of parahydrogen as the probe of choice [4]. The reasons for this are that not only its transition energy [4] but also its underlying line shape [5,6] are sensitive probes of the local environment and the instruments generally have their best resolution in this energy region.The disadvantage of studying the rotational transition is that it is very difficult to model. This has been done with either a phenomenological model of how the rotational energy levels behave in an applied potential [4] or have required very sophisticated multi-dimensional ab initio calculations [7]. These difficulties could be reduced by studying the fundamental H-H stretch vibration at 516 meV, because the calculation is now a conventional lattice dynamics problem, which is tractable with density functional theory [8].

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Section: Solid and Liquid H2mentioning

confidence: 54%

Section: Solid and Liquid H2mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

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Observation of the stretch mode in H₂ and D₂ by inelastic neutron scattering spectroscopy

Parker

Ewings

Fernandez-Alonso

et al. 2018

J. Phys.: Conf. Ser.

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Neutron Diffraction

Yousufuddin¹,

Bau²

2005

Encyclopedia of Inorganic Chemistry

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The following article reviews the technique of neutron diffraction and its effectiveness in probing materials of chemical interest. The main advantage of neutrons is their ability to detect hydrogen atoms. We describe in this article several examples where neutrons offered additional information that was otherwise unavailable from X‐rays. We have summarized a number of structures studied using neutron diffraction. Most of these structures showed the precise location of chemically interesting hydrogen atoms. We have also summarized structures where neutron diffraction allowed for the assignment of absolute stereochemistry in deuterated systems. Lastly, we have discussed the usefulness of neutron diffraction in protein crystallography. One of the major disadvantages of neutron diffraction is the immensely low number of neutron sources available as compared to X‐ray sources. We have detailed the neutron sources around the world capable of neutron diffraction experiments, including sources that are currently under construction such as the Spallation Neutron Source in Oak Ridge, TN and J‐PARC in Tokyo, Japan. In addition, a number of neutron diffraction instruments and their sample requirements are illustrated. In the past, neutron diffraction has been overlooked by most practicing chemists as an efficient analytical tool. However, with the newer more powerful facilities and instrumentation in development, chemical systems studied with neutrons should become more common.

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Neutron Scattering

Larese

2005

Encyclopedia of Inorganic Chemistry

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Neutron scattering, which includes diffraction (ND), inelastic (INS), quasi‐elastic (QENS), and transmission/absorption techniques, is one of the most direct ways to probe the microscopic structure, dynamics, and compositional distribution of bulk condensed matter. The properties of the neutron include: no charge; a mass, m n , equal to 1.675 × 10 −27 kg; and a magnetic moment, μ n , equal to 0.9662 × 10 −26 J T −1 . Although neutrons scatter weakly, but more or less uniformly, from the nucleus of most elements across the periodic table, there are several elements that scatter neutrons rather well. Neutrons are extremely good for investigating compounds bearing light elements, especially hydrogen, deuterium, carbon, and oxygen as well as magnetic compounds. A representative sample of the scattering properties of different nuclei (see Table 2) has been tabulated (including a graphic illustration). This is in stark contrast to X‐ray scattering, in which the principal interaction (and scattering) of the massless X‐ray photon is from the electron cloud; so the scattering amplitude increases with the atomic number. Hence, neutrons are a very versatile probe of condensed matter and have been used to characterize the atomic arrangement in crystalline and amorphous solids and liquids (magnetic materials in particular) via diffraction, lattice vibrations, molecular motion, and diffusion (both rotational and translational). Neutron beams with energies (1 meV–1 eV) and wavelengths (0.5–20 Å) are ideally suited for investigating condensed matter and can be produced in two ways. The first is from a reactor source, where a purposefully built, steady state or pulsed reactor produces neutrons as the result of nuclear fission. The second is the spallation source, where a steady or pulsed stream of energetic protons collides with a solid or liquid target; the resulting collision and thermalization process causes neutrons to be knocked out or spalled from the target. The energy and wavelength of these neutron beams can be adjusted using thermal moderators chosen to shift the peak in the energy distribution of the beam. Specially designed instrumentation that uses either crystal optics or time‐of‐flight (TOF) methods, is used to analyze the angular and energy distribution of the scattered neutrons as a result of the physical processes from the sample under study. This contribution will briefly review the production and instrumentation at both reactor and steady state sources. Because of the vast number of studies that have been performed using thermal neutrons, only a limited set of examples of how neutrons have been used to characterize crystal structure, dynamic modes in solids (phonons), diffusion and phase transformations of inorganic materials can be presented here. Finally, a brief introduction will be provided for the use of neutrons to investigate surface states of adsorbed species because, with the advent of new high intensity neutron sources and the production of nanometer scale materials with high surface to volume ratios, it is a topic that is undoubtedly going to receive significant attention in the near future.

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Vibrational Spectroscopy with Neutrons

Cited by 329 publications

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Observation of the stretch mode in H₂ and D₂ by inelastic neutron scattering spectroscopy

Observation of the stretch mode in H₂ and D₂ by inelastic neutron scattering spectroscopy

Neutron Diffraction

Neutron Scattering

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Vibrational Spectroscopy with Neutrons

Cited by 329 publications

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Observation of the stretch mode in H2 and D2 by inelastic neutron scattering spectroscopy

Observation of the stretch mode in H2 and D2 by inelastic neutron scattering spectroscopy

Neutron Diffraction

Neutron Scattering

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Observation of the stretch mode in H₂ and D₂ by inelastic neutron scattering spectroscopy

Observation of the stretch mode in H₂ and D₂ by inelastic neutron scattering spectroscopy