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Recently we reported a novel “roaming” dissociation pathway of formaldehyde in which one of the H atoms strays far from the minimum energy reaction path, explores a broad region of the potential energy surface, then abstracts the remaining H atom to form molecular products, without going near the configuration of the conventional transition state saddle point. The detailed dynamics of the abstraction mechanism and its energy dependence have already been reported. Here, with a combination of experimental and theoretical results, we examine the roaming behavior at the energetic extremes. We show evidence of roaming below the threshold of the radical dissociation channel and consider the implications of this and the possible existence of a transition state for the roaming mechanism. We also show the occurrence of roaming up to 3200 cm−1 above the threshold of the triplet dissociation channel. In addition, we present results affording deeper insight into the dynamics of the roaming mechanism: we show evidence of roaming leading to CO in v = 1, and examine the issue of nuclear spin conservation during dissociation via the roaming mechanism.  相似文献   
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For a compact totally ordered space X, K. H. Hofmann and P. S. Mostert constructed a topological semigroup Irr (X)0 such that every compact irreducible semigroup with idempotents X is a surmorphic image of Irr (X)0 [2]. J. H. Carruth and M. Mislove pointed out that Irr (X)0 was in general not a compact semigroup. In this paper a compact connected hormos will be constructed which contains Irr (X)0 as a dense subsemigroup and for which every compact irreducible semigroup with idempotents X is a surmorphic image. This leads to a new proof of the existence of generators for the category of compact irreducible semigroups with idempotents X. It will then be shown that Irr (X)0 contains generators for the category.  相似文献   
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ENDOR frequencies of randomly oriented triplets have been measured from the fast Fourier transform of electron spin echo envelope modulation. Important experimental conditions are low temperatures, high microwave power and long phase memory time in a proper form of solvent. The technique is exemplified by using diphenylmethylenes in rigid glasses, polycrystalline forms and single crystals of benzophenones.  相似文献   
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The electron spin echo envelope modulation of the chlorophyll a radical cation has been examined for radicals containing 14N and 15N. The modulation is found to be due primarily to the nitrogen nuclei in the heterocycle and the nuclear quadrupole interaction plays a large part in determining the modulation from 14N. The modulation from 15N allows limits to be set on the isotropic and anisotropic hyperfine interactions.  相似文献   
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An analysis is given for the expansion (60 terms) of a gamma function ratio discussed by Stieltjes and others. A Stieltjes continued fraction is derived, affording lower and upper bound (but lacking a rigorous proof), along with continued fraction for the odd and even series.  相似文献   
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Powders of three hexagonal metal-hydrides or -deuterides are found to align in 4.4–8.3 T magnetic fields used for NMR. The field-alignment is unexpected, since all three systems have very small susceptibilities, as demonstrated by sharp NMR lines. The extent of alignment runs from nearly complete to barely detectable in ZrBe2(H,D)x, LuD3, and YD3, respectively. The preferred alignment direction in ZrBe2(H,D)x is with the crystallites’ c-axis perpendicular to B, while the c-axis and B tend to be parallel in LuD3 and YD3. The susceptibilities χ|| and χ are determined from bulk magnetization measurements in aligned ZrBe2H1.4 powder. The alignment must be considered for proper analysis of NMR spectra in these and related materials.  相似文献   
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