Hydrogenated carbon nitride is synthesized by polymerization of 1,5-naphthyridine, a nitrogen-containing heteroaromatic compound, under high-pressure and high-temperature conditions. The polymerization progressed significantly at temperatures above 573 K at 0.5 GPa and above 623 K at 1.5 GPa. The reaction temperature was relatively lower than that observed for pure naphthalene, suggesting that the reaction temperature is considerably lowered when nitrogen atoms exist in the aromatic ring structure. The polymerization reaction largely progresses without significant change in the N/C ratio. Three types of dimerization are identified; naphthylation, exact dimerization, and dimerization with hydrogenation as determined from the gas chromatograph-mass spectrometry analysis of soluble products. Infrared spectra suggest that hydrogenation products were likely to be formed with spa carbon and NH bonding. Solid-state C-13 nuclear magnetic resonance reveals that the sp(3)/sp(2) ratio is 0.14 in both the insoluble solids synthesized at 0.5 and 1.5 GPa. Not only the dimers but also soluble heavier oligomers and insoluble polymers formed through more extensive polymerization. The major reaction mechanism of 1,5-Nap was common to both the 0.5 and 1.5 GPa experiments, although the required reaction temperature increased with increasing pressure and aromatic rings preferentially remained at the higher pressure.

The insoluble organic material (IOM) in primitive chondritic meteorites is very enriched in D (up to delta D = 3500% in bulk). Based largely on a series of electron paramagnetic resonance (EPR) studies of IOM from three meteorites (Orgueil, Murchison and Tagish Lake), it has been suggested that these enrichments are the result of exchange with H2D+ in the solar nebula and that exchange with radicals in the IOM was particularly facile so that they are enormously enriched in D (dD > 95000%). To try to test whether radicals are largely responsible for the D enrichments in IOM, we have used EPR to measure the radical concentrations (spins/g) and g-factors of 18 IOM separates from C1-2 chondrites of varying petrologic type and chemical group that have a much wider range of H isotopic compositions (dD = 600-3500%) than in previous studies. We confirm the previous studies findings that IOM exhibits non-Curie law behavior and that it does not completely saturate even at microwave excitation powers of 200 mW. We also have obtained similar g-factor values. However, our IOM samples typically exhibit a lower and more limited range of spin concentrations, and smaller deviations from Curie law behavior than in previous studies. Nor do we observe correlations between bulk dD and either spins/g or non-Curie law behavior that would be expected if exchange between H2D+ and radicals, as previously proposed, was the cause of the D-enrichments in IOM. Indeed, in general the radical concentrations and the degree of non-Curie law behavior do not seem to correlate with any of the measured IOM properties, with chondrite group or parent body history (e.g., degree of aqueous alteration). The only exceptions are the IOM in four Tagish Lake lithologies whose spin concentrations increase with increasing degree of thermal processing as indicated by decreasing H/C and dD, and increasing aromaticity. (C) 2021 Elsevier Ltd. All rights reserved.

The large variations in hydrogen isotope ratios found in insoluble organic matter (IOM) in chondritic meteorites may be attributed to hydrogen isotopic exchange between IOM and water during aqueous alteration. We conducted D-H exchange experiments (1) during synthesis of IOM simulant (hereafter called chondritic organic analog, COA) from formaldehyde, glycolaldehyde, and ammonia with water, and (2) with the synthesized COA with a secondary reservoir of water. The changes in the D/H ratios obtained by infrared spectra of the COA suggest that most of the hydrogen in the COA is derived from water during synthesis. We further investigated the kinetics of D-H exchange between D-rich COA and D-poor water, as well as the opposite case, D-poor COA and D-rich water. To help assess understanding exchange kinetics, two-dimensional isotope imaging obtained using isotope microscope revealed that no gradient D-H exchange profiles were present in the COA grains, indicating that the rate-limiting step for D-H exchange is not diffusion. Thus, the changes in D/(D + H) ratios were fit by the first-order reaction rate law. Apparent kinetic parameters-the rate constants, the activation energies, and the frequency factors-were obtained with the Arrhenius equation. Using these kinetic expressions, hydrogen isotopic exchange profiles were estimated for time and temperature behavior. The D-H exchange between organic matter and water is apparently relatively fast and this implies that the aqueous alteration temperatures should have been very low, likely close to 0 degrees C to maintain hydrogen isotopic disequilibrium between organic matter and liquid water for millions of years.

The interpretation of low-resistivity anomalies in the lithospheric mantle of several cratonic regions has invoked hydrogen, or connected networks of graphite with iron-rich silicates, and/or metal sulfides. Electrical laboratory measurements are a powerful approach for exploring these alternatives. We report electrical measurements of two xenoliths (pyroxenite and dunite) from Tanzania; two metal sulfides (FeS and Fe-S-Ni); and several mixtures of metal sulfides (3.4-18.2 vol.%) with xenolith. A multi-anvil press was employed to maintain a 2 GPa pressure and temperatures up to 1,627 K. The addition of 3.4 vol.% FeS to the pyroxenite or dunite matrix has little effect on bulk resistivity, particularly for T > 800 K. However, the resistivity drops dramatically-by factors of up to 1,000, depending on temperature-upon addition of 6.5 vol.% FeS in the dunite. Addition of 18.2% FeS causes a further decrease of the same magnitude relative to the 6.5% sample. Scanning electron microscope images do not reveal the formation of a connected FeS network as part of the decreased resistivity. Possible explanations for the apparently conflicting results include connections of the sulfide that are not imaged in the back-scattered images, either because of limited resolution, or perhaps the inherent limitations of the 2-D perspective. The complete data set (xenoliths, metal sulfides, and mixtures) was modeled with a modified version of Archie's law, and we find satisfactory agreement over a truncated temperature range. We conclude that the low-resistivity anomalies in Tanzania, Kaapvaal, and Gawler cratons can be explained by the presence of a few vol.% of solid sulfide.

The apparent end of the internally generated Martian magnetic field at 3.6-4.1 Ga is a key event in Martian history and has been linked to insufficient core cooling. We investigate the thermal and magnetic evolution of the Martian core and mantle using parameterized models and considered three improvements on previous studies. First, our models account for thermal stratification in the core. Second, the models are constrained by estimates for the present-day areotherm. Third, we consider core thermal conductivity, kc, values in the range 5-40 W m(-1) K-1 as suggested by recent experiments on iron alloys at Mars core conditions. The majority of our models indicate that the core of Mars is fully conductive at present with core temperatures greater than 1940 K. All of our models are consistent with the range of k(c)=16-35 W m(-1) K-1. Models with an activation volume of 6 (0) cm(3) mol(-1) require a mantle reference viscosity of 10(19)-10(20)(10(20)-10(21)) Pa s.