Theoretical and electron spin resonance studies of the H⋯H, H⋯D, and D⋯D spin-pair radicals in rare gas matrices: A case of extreme singlet–triplet mixing

Knight, Lon B.; Rice, William E.; Moore, Louie; Davidson, Ernest R.; Dailey, Robert S.

doi:10.1063/1.476714

Cited by 38 publications

(11 citation statements)

References 39 publications

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“…It was found that the g factors and hyperfine interactions of D atoms in the D-D 2 -He solids and in the D-D 2 -Ne-He solids are similar to each other and very close to those obtained for D atoms stabilized in a solid D 2 matrix. 32,37 From the investigation of the saturation behavior of the ESR lines of the D atoms, a relatively short spinlattice relaxation time, T 1 ϭ3ϫ10 Ϫ3 s, was found. All these observations show that D atoms were mainly stabilized inside D 2 clusters.…”

Section: Discussionmentioning

confidence: 99%

Deuterium atoms and molecules in nanoclusters of molecular deuterium

et al. 2004

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Impurity-helium solids created by injecting deuterium atoms and molecules into superfluid 4 He have been studied via x-ray-diffraction and electron-spin-resonance ͑ESR͒ techniques. X-ray-diffraction measurements show that these solids are highly porous gel-like structures consisting of D 2 clusters with the characteristic cluster size of 90Ϯ30 Å. The densities of D 2 molecules in the samples are 7ϫ10 20 -3ϫ10 21 cm Ϫ3 . Each of the D 2 clusters are either partially or totally surrounded by thin layers of adsorbed helium which may play an important role in preventing the coalescence of the clusters into larger crystallites of solid D 2 . Using ESR, we find that average concentrations of D atoms of order 1ϫ10 18 cm Ϫ3 can be achieved in our samples. Measurements of the ground-state spectroscopic parameters and relaxation times of atomic deuterium show that the D atoms reside in the D 2 clusters. The combined x-ray and ESR data show that local concentrations of D atoms as large as 2ϫ10 19 cm Ϫ3 are obtained in our experiments. The highly porous deuterium nanostructures studied in this work are promising for the production of high concentrations of ultracold neutrons and for significant nuclear polarization of D 2 molecules by the ''brute force method'' at low temperatures.

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Section: Discussionmentioning

confidence: 99%

Deuterium atoms and molecules in nanoclusters of molecular deuterium

et al. 2004

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“…H • , H 2 +• , and H 4 +• are experimentally known. The isotropic hyperfine coupling constant (iHFCC) of H • in noble gases varies between 501.0 and 512.3 G . Experimental iHFCCs for H 2 +• in various vibrational and rotational states are available. , The value for ν = 0, N = 1 is 329.3 G. Calculations suggest 333.9 G for ν = 0, N = 0 and 334.3 G at an internuclear distance of 1.0584 Å .…”

Section: Introductionmentioning

confidence: 99%

Gaussian Basis Sets for Highly Accurate Calculations of Isotropic Hyperfine Coupling Constants at Hydrogen

Fau

Bartlett

2003

J. Phys. Chem. A

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ESR spectroscopy is an important method for characterizing radicals. However, the isotropic hyperfine coupling constants are difficult to calculate. The effects of solvent and molecular vibration are often not negligible. We provide benchmark values near the full CI, complete basis set limit for nonvibrating H • , H 2 +• , and H 4 +• in the gas phase. These are used to judge the performance of already existing and newly constructed basis sets. The new (aug-)cc-pVXZ-t5s basis sets are superior to previous basis sets. They have average errors between -0.4 and -0.1% of the reference values. The rms deviation from the average error is less than 0.2%. Only extreme contraction significantly increases the errors. Larger valence basis sets improve the accuracy.

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“…Earlier, Knight et al , [5] who studied by computer modeling the EPR spectra of hydrogen atoms in matrices of noble gases in the range of forbidden transition, discovered the existence of weakly bound hydrogen pairs [5]. The formation of hydrogen pairs, a the peculiar way to deposit atomic hydrogen, was also reported in other media.…”

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confidence: 95%

Weakly bound hydrogen and deuterium pairs in UV-photosensitized frozen aqueous solutions of KH2PO4 and KD2PO4

Dobryakov

Brzhewska

Lozinova

et al. 2004

Dokl Biochem Biophys

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Interesting chemical models, including several examples of ATP photosynthesis initiated by different kinds types of irradiation [1], were elaborated in study of mechanism of elementary chemical act of ATP synthesis. Paramagnetic compounds are generated under such conditions. To reveal the leading free radical intermediate of the reaction is essential for careful analysis of its EPR spectra by computer modeling.The lines of hydrogen atoms with a splitting of 508 G are revealed in EPR spectra at 77 K during UV irradiation of phosphate, a substrate of the reaction. These lines, and wasare also detected in the presence of the sensitizer adenine during irradiation by light with λ > 260 nm. In contrast to the signals of free-radical phosphates detected in EPR spectra at a sufficiently relatively high power of microwave irradiation ( P > 1.6 mW) and well detected at P > 20 mW, these signals became already saturated at P values as low as 0.1 mW. At very low power values of power ( P 0 .004 mW), when the signal of the phosphate radical is not detectable, EPR spectra along with hydrogen signal contain a doublet in the range g ~ 2.00. EPR spectra of hydrogen atoms are well known for different media; however, but the central signals that often are often present in irradiated systems are usually attributed to the radicals not bound with hydrogen [2][3][4].We hypothesized that the satellite central line (triplet EPR spectra) detected in EPR spectra is caused by isotropic exchange interaction between of hydrogen atoms in weakly bound hydrogen pairs. Earlier, Knight et al. ,[5] who studied by computer modeling the EPR spectra of hydrogen atoms in matrices of noble gases in the range of forbidden transition, discovered the existence of weakly bound hydrogen pairs [5]. The formation of hydrogen pairs, a the peculiar way to deposit atomic hydrogen, was also reported in other media. It is important that a in that way hydrogen atom thus stabilized, under proper conditions, may be released and implicated participate in chemical and cross-linking processes [6,7].Of special interest is the role of atomic hydrogen in the photochemical model of ATP synthesis, because as fixing hydrogen orthophosphate, which fixes hydrogen, is a substrate of this reaction. It is noteworthy that atomic hydrogen has a high stability, especially in phosphates, sometimes at temperatures up to room temperature [8]. The nature of this phenomenon is clarified by a detailed computer analysis of its EPR spectrum using an original four-spin program.The search for optimal values of parameters values for the description of experimental spectra was performed by variation of values of variable parameters in the model spectra. The mMinimum of the sum of squared deviations served as a criterion for concordance between the calculated theoretical and the experimental EPR spectra.For the isotropic spin Hamiltonian (for the sake of simplicity and counting rate increase, all anisotropic interactions in Hamiltonian were neglected in Hamiltonian) the system of equations disinte...

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Theoretical and electron spin resonance studies of the H⋯H, H⋯D, and D⋯D spin-pair radicals in rare gas matrices: A case of extreme singlet–triplet mixing

Cited by 38 publications

References 39 publications

Deuterium atoms and molecules in nanoclusters of molecular deuterium

Deuterium atoms and molecules in nanoclusters of molecular deuterium

Gaussian Basis Sets for Highly Accurate Calculations of Isotropic Hyperfine Coupling Constants at Hydrogen

Weakly bound hydrogen and deuterium pairs in UV-photosensitized frozen aqueous solutions of KH2PO4 and KD2PO4

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