Spin Statistics Isomerization in Methane

Curl, R. F.; Kasper, J. V. V.; Pitzer, Kenneth S.; Sathianandan, K.

doi:10.1063/1.1726686

Cited by 22 publications

(10 citation statements)

References 3 publications

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“…Such an approach [58,59] yields Γ ≃ 1.8•10 8 s −1 /torr which is indeed close to the level population decay rate 1•10 8 s −1 /torr [57]. The various mixing processes in CH 3 F are illustrated in Table 1 where the contributions to the conversion are calculated assuming the From the data in Table 1 one can see that the conversion in 12 CH 3 F by spin-spin interaction is much slower than in 13 CH 3 F. On the other hand, in 12 CH 3 F the spin-rotation interaction was predicted to be the leading mechanism [60,50]. The key point is the right choice of the decoherence rate Γ for the most important level pair in 12 CH 3 F: (28,5)- (27,6).…”

Section: Chsupporting

confidence: 59%

“…One may hope that the enrichment will be retained after fast evaporation of these molecules into the gas phase. In paper [12] an attempt was made to separate spin isomers of methane using rapid heating of a solid held at low temperature. In a subsequent paper [13] (see also [14]), these authors attributed the negative result of [12] to fast conversion due to the degeneracy of methane states having different spin symmetry.…”

Section: Other Moleculesmentioning

confidence: 99%

“…In paper [12] an attempt was made to separate spin isomers of methane using rapid heating of a solid held at low temperature. In a subsequent paper [13] (see also [14]), these authors attributed the negative result of [12] to fast conversion due to the degeneracy of methane states having different spin symmetry. Yet this issue deserves further investigation because fast (although in a different time range) cooling of methane in a molecular jet is not accompanied by spin conversion [15,16,17].…”

Section: Other Moleculesmentioning

confidence: 99%

“…A search for close ortho-para level pairs in CH 3 F was performed in [45]. At the time, a complete set of ground state molecular parameters was available for 12 CH 3 F only [52]. For 13 CH 3 F the molecular parameters A 0 and D K 0 were missing.…”

Section: Ortho-para State Mixing In Ch 3 Fmentioning

confidence: 99%

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NUCLEAR SPIN CONVERSION IN POLYATOMIC MOLECULES

Chapovsky

Hermans

1999

Annu. Rev. Phys. Chem.

148

110

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Except for ortho- and para-H2, little is known about nuclear spin isomers (or spin modifications) of molecules. The main reason is the lack of practical enrichment techniques. Recently, a few enrichment methods were developed, which opened up new possibilities in the field. These methods are briefly reviewed. Substantial progress in the field has been made by the introduction of light-induced drift as a gas-phase separation tool. This is illustrated by extensive data on CH3F, which reveal that the gas-phase ortho-para conversion is governed by intramolecular mixing of the nuclear spin states. The role of direct ortho-para transitions is small. Various aspects of the conversion were investigated in detail: pressure and collision partner dependence, isotope effect, and temperature dependence. The most decisive information on the spin conversion mechanism is derived from the observation of level-crossing resonances in an electric field and the quantum Zeno effect induced by collisions.

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Section: Chsupporting

confidence: 59%

Section: Other Moleculesmentioning

confidence: 99%

Section: Other Moleculesmentioning

confidence: 99%

Section: Ortho-para State Mixing In Ch 3 Fmentioning

confidence: 99%

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NUCLEAR SPIN CONVERSION IN POLYATOMIC MOLECULES

Chapovsky

Hermans

1999

Annu. Rev. Phys. Chem.

148

110

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“…In modern science, of significant interest are the properties of NSIM, including their interconversion processes (Chapovsky and Hermans, 1999) and NSIM behavior upon phase transitions (Curl et al, 1966;Hama et al, 2018), the NSIM-related selection rules in molecular spectroscopy (Kanamori et al, 2017;Ozier et al, 1970) Kilaj et al, 2018;Oka, 2004), NSIM in astrophysics and astrochemistry research (Hama and Watanabe, 2013;Hily-Blant et al, 2018;Shinnaka et al, 2016;Tielens, 2013), and more. So far, however, most heterogeneous catalysts demonstrated a limited efficiency in the pairwise hydrogen addition, or in some cases the low yields of the desired product, or both (Kovtunov et al, 2013(Kovtunov et al, , 2016(Kovtunov et al, , 2020a.…”

mentioning

confidence: 99%

Pd-based bimetallic catalysts for HET-PHIP

Burueva

Stakheev

Koptyug

2021

Preprint

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Abstract. Production of hyperpolarized catalyst-free gases and liquids by heterogeneous hydrogenation with parahydrogen (HET-PHIP) can be useful for various technical as well as biomedical applications, including in vivo studies, investigations of mechanisms of industrially important catalytic processes, enrichment of nuclear spin isomers of polyatomic gases, and more. In this regard, the wide systematic search for heterogeneous catalysts effective in pairwise H2 addition required for the observation of PHIP effects is crucial. Here in this work we demonstrate the competitive advantage of Pd-based bimetallic catalysts for HET-PHIP. The dilution of catalytically active Pd with less active Ag or In atoms provides the formation of atomically dispersed Pd1 sites on the surface of Pd-based bimetallic catalysts, which are significantly more selective toward pairwise H2 addition compared to the monometallic Pd. Furthermore, the choice of the dilution metal (Ag or In) has a pronounced effect on the efficiency of bimetallic catalysts in HET-PHIP, as revealed by comparing Pd-Ag and Pd-In bimetallic catalysts.

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Nuclear spin state relaxation of formaldehyde in mixtures with inert gases

Peters

Schramm

1998

Ber Bunsenges Phys Chem

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Measurements of the rate constant of the ortho‐para conversion of monomeric gaseous formaldehyde H2CO in mixtures with He, Ar, H2, N2, CO, O2, CH3F and SF6 are described. Separation of the nuclear spin isomers of formaldehyde was obtained by selective UV laser photolysis of ortho‐formaldehyde in the natural ortho‐para mixture. Inert gas pressure was varied up to atmospheric pressure, formaldehyde pressure was 2.8 mbar in all experiments. At low pressures a linear increase of the rate constant with the inert gas pressure was found in all gases. With the noble gases, this increase was very small. In mixture with H2, N2, O2 and SF6 the rate constant rises up to a maximum and then shows a steep decrease as a function of the inert gas pressure. With the noble gases, CO and CH3F only the increase of the rate constant with pressure could be measured. The results are compared to the theory of Curl et al. [37]for the pressure dependence of the nuclear spin state relaxation of formaldehyde.

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Spin Statistics Isomerization in Methane

Cited by 22 publications

References 3 publications

NUCLEAR SPIN CONVERSION IN POLYATOMIC MOLECULES

NUCLEAR SPIN CONVERSION IN POLYATOMIC MOLECULES

Pd-based bimetallic catalysts for HET-PHIP

Nuclear spin state relaxation of formaldehyde in mixtures with inert gases

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