Nuclear spin selection rules in chemical reactions by angular momentum algebra

Oka, Takeshi

doi:10.1016/j.jms.2004.08.015

Cited by 105 publications

(138 citation statements)

References 16 publications

(27 reference statements)

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“…A careful theoretical study was necessary to explain all the results. Indeed, although the use of nuclear-spin selection rules (Oka 2004), leads to the reproduction of most of the observed OPR values below three at reasonable temperatures (Le Gal et al 2014a,b), it was necessary to identify a mechaArticle number, page 1 of 12 arXiv:1708.08980v2 [astro-ph.GA] 1 Oct 2017 A&A proofs: manuscript no. H2CL+_manuscript_accepted_2columns nism able to at least partially thermalize the OPR at the very low temperatures where the thermal OPR exceeds three and goes to infinity as the temperature goes to 0 K. This need led Persson et al (2016) to consider a process previously omitted in models: the poorly studied H + NH 2 H-atom exchange reaction to interconvert NH 2 between its ortho and para forms, thus increasing the OPR with decreasing temperature.…”

Section: Introductionmentioning

confidence: 99%

“…Indeed, even an understanding of what appear to be thermal values under interstellar conditions can require a detailed analysis. Once well understood, OPRs can afford new powerful astrophysical diagnostics on the chemical and physical conditions of their environments, and in particular can trace their history, provided that the memory of a chemical process can be propagated and preserved in the molecular level population distributions (Oka 2004;Faure et al 2013;Le Gal et al 2014a). …”

Section: Introductionmentioning

confidence: 99%

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The ortho-to-para ratio of H₂Cl⁺: Quasi-classical trajectory calculations and new simulations in light of new observations

Gal

Xie

Herbst

et al. 2017

A&A

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Multi-hydrogenated species with proper symmetry properties can present different spin configurations, and thus exist under different spin symmetry forms, labeled as para and ortho for two-hydrogen molecules. We investigated here the ortho-to-para ratio (OPR) of H 2 Cl + in the light of new observations performed in the z=0.89 absorber toward the lensed quasar PKS 1830−211 with the Atacama Large Millimeter/submillimeter Array (ALMA). Two independent lines of sight were observed, to the southwest (SW) and northeast (NE) images of the quasar, with OPR values found to be 3.15±0.13 and 3.1±0.5 in each region, respectively, in agreement with a spin statistical weight of 3:1. An OPR of 3:1 for a molecule containing two identical hydrogen nuclei can refer to either a statistical result or a high-temperature limit depending on the reaction mechanism leading to its formation. It is thus crucial to identify rigorously how OPRs are produced in order to constrain the information that these probes can provide. To understand the production of the H 2 Cl + OPR, we undertook a careful theoretical study of the reaction mechanisms involved with the aid of quasi-classical trajectory calculations on a new global potential energy surface fit to a large number of high-level ab initio data. Our study shows that the major formation reaction for H 2 Cl + produces this ion via a hydrogen abstraction rather than a scrambling mechanism. Such a mechanism leads to a 3:1 OPR, which is not changed by destruction and possible thermalization reactions for H 2 Cl + and is thus likely to be the cause of observed 3:1 OPR ratios, contrary to the normal assumption of scrambling.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

The ortho-to-para ratio of H₂Cl⁺: Quasi-classical trajectory calculations and new simulations in light of new observations

Gal

Xie

Herbst

et al. 2017

A&A

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“…This ranges from the astronomical importance of the ortho-para ratio [1][2][3][4][5] , to studies of nuclear-spin conversion [6,7] , selection rules and reactive collisions [8][9][10] or symmetry breaking [11] . Spin-enriched samples furthermore would allow for hypersensitized NMR experiments via polarization transfer reactions [12][13][14] .…”

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confidence: 99%

Separating Para and Ortho Water

et al. 2014

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Water exists as two nuclear-spin isomers, para and ortho, determined by the overall spin of its two hydrogen nuclei. For isolated water molecules the conversion between these isomers is forbidden and they act as different molecular species. Yet, these species are not readily separated and no pure para sample has been produced. Accordingly, little is known about their specific physical and chemical properties, conversion mechanisms, or interactions. Here, we demonstrate the production of isolated samples of both spin isomers in pure beams of para and ortho water in their respective absolute ground state. These single-quantum-state samples are ideal targets for unraveling spin-conversion mechanisms, for precision spectroscopy and fundamentalsymmetry-breaking studies, and for spin-enhanced applications, e. g., laboratory astrophysics and -chemistry or hypersensitized NMR experiments.Significant efforts have been undertaken to separate and study the nuclear-spin isomers of water, motivated by their importance in a wide variety of scientific disciplines. This ranges from the astronomical importance of the ortho-para ratio [1][2][3][4][5] , to studies of nuclear-spin conversion [6,7] , selection rules and reactive collisions [8][9][10] or symmetry breaking [11] . Spin-enriched samples furthermore would allow for hypersensitized NMR experiments via polarization transfer reactions [12][13][14] . However, unlike other small polyatomic molecules exhibiting spin isomerism, such as fluoromethane or ethylene [15,16] , which were spin-isomerically enriched using the light induced drift technique [7] , this has not been achieved for water. Separation through selective adsorption on surfaces was reported [17] , but these results remain controversial and could not be reproduced [18][19][20][21] . Thus, studies of spin-conversion dynamics in water have been limited to water embedded in rare gas matrices, with relative spin populations modified by the sample temperature [22] . A recent study investigated nuclear-spin conversion in the gas-phase and found no spin conversion for water monomers [23] .Recently, the production of a single spin isomer of water in a magnetic-hexapole-focuser setup was demonstrated [24] . One of the magnetically active spin projections (m = +1) of ground-state ortho water was magnetically focused into the interaction volume, while all other spin-projection states were defocused or diverged unaffected by the field. The purity of the produced ortho beam was later evaluated as 93 %, with simulations suggesting an upper limit for the achievable purity of 97 % [24,25] .Here, we experimentally demonstrate the production of pure samples of both, para and ortho water, the latter further separated into its M = 0 and M = 1 angular momentum projections, in the gas-phase. The produced single-quantum-states are ideally suited for further experiments on nuclear-spin conversion under collision-free conditions, nuclear-spin-dependent reactivity [8] , trapping of single spin-isomer samples in electromagnetic traps [26] ...

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“…60 We will assume a general reaction H 3 + + X → HX + + H 2 whose mechanism is a direct proton hop (i.e., no complex is formed that can result in proton scrambling prior to dissociation). When the reaction involves o-H 3 + , application of Oka's angular momentum algebra 37 quickly shows that only o-H 2 can be formed as formation of p-H 2 would violate conservation of total nuclear spin angular momentum. Although the angular momentum algebra only gives proper branching ratios in the high-temperature limit, this selection rule for the chemical reaction also applies at the low temperatures relevant for cold interstellar clouds.…”

Section: Discussionmentioning

confidence: 99%

“…From a chemical physics standpoint, this reaction exhibits selection rules based on the symmetries of the reactants' rovibronic and nuclear spin state, 36 or alternatively, the selection rules can be derived in terms of nuclear spin angular momentum algebra. 37 Because of the weakness of the nuclear magnetic interaction, the two nuclear spin modifications (o-H 3 + , angular momentum I = (3/2), symmetry Γ ns = A 1 ; p-H 3 + , I = (1/2), Γ ns = E) can be regarded as separate chemical species; interconversion can only take place by means of reactive collisions or by interaction with a strong inhomogeneous magnetic field. As such, the H 3 + + H 2 → H 2 + H 3 + reaction has seen considerable theoretical treatment, especially in recent years, 38−41 and the effects of the nuclear spin selection rules have been experimentally studied by highresolution spectroscopy of H 3 + in hydrogenic plasmas.…”

Section: Introductionmentioning

confidence: 99%

On the Symmetry and Degeneracy of H₃⁺

Crabtree

McCall

2013

J. Phys. Chem. A

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The fundamental molecular ion H 3 + has impacted astronomy, chemistry, and physics, particularly since the discovery of its rovibrational spectrum. Consisting of three identical fermions, its properties are profoundly influenced by the requirements of exchange symmetry, most notably the nonexistence of its ground rotational state. Spectroscopy of H 3 + is often used to infer the relative abundances of its two nuclear spin modifications, ortho-and para-H 3 + , which are important in areas as diverse as electron dissociative recombination and deuterium fractionation in cold interstellar clouds. In this paper, we explore in detail the impact of exchange symmetry on the states of H 3 + , with a particular focus on the state degeneracies necessary for converting spectral transition intensities to relative abundances. We address points of confusion in the literature surrounding these issues and discuss the implications for proton-transfer reactions of H 3 + at low temperatures.

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Nuclear spin selection rules in chemical reactions by angular momentum algebra

Cited by 105 publications

References 16 publications

The ortho-to-para ratio of H₂Cl⁺: Quasi-classical trajectory calculations and new simulations in light of new observations

The ortho-to-para ratio of H₂Cl⁺: Quasi-classical trajectory calculations and new simulations in light of new observations

Separating Para and Ortho Water

On the Symmetry and Degeneracy of H₃⁺

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Nuclear spin selection rules in chemical reactions by angular momentum algebra

Cited by 105 publications

References 16 publications

The ortho-to-para ratio of H2Cl+: Quasi-classical trajectory calculations and new simulations in light of new observations

The ortho-to-para ratio of H2Cl+: Quasi-classical trajectory calculations and new simulations in light of new observations

Separating Para and Ortho Water

On the Symmetry and Degeneracy of H3+

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Product

Resources

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The ortho-to-para ratio of H₂Cl⁺: Quasi-classical trajectory calculations and new simulations in light of new observations

The ortho-to-para ratio of H₂Cl⁺: Quasi-classical trajectory calculations and new simulations in light of new observations

On the Symmetry and Degeneracy of H₃⁺