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Electrothermal stimulation of chemical reactions in mixture of calcite and silicon powders
Published in Genadiy Pivnyak, Volodymyr Bondarenko, Iryna Kovalevska, Theoretical and Practical Solutions of Mineral Resources Mining, 2015
Ion-carbonate [CO3]2-, which is formed at the initial stage of CaCO3 decomposition, in the field of active center on the surface of silicon (or Ca2+ ions) is resolved to atomic carbon and oxygen. One part of the oxygen oxidizes the calcium ions (Ca2+), and another is captured by active centers, resulting in the stabilization on the quartz surface, for example, ≡SiO3 radical. A similar way is considered by authors using physical and mathematical modeling of elementary chemical acts occurring on the surface of diamond particles. Upon reaching the critical concentration of atomic carbon in the intergranular space system due to fluctuations of the energy and density (and possibly resonance phenomena) new phase of condensed carbon is formed spontaneously, which is correspond to the kinetic theory (Folmer 1986).
Can third-body stabilisation of bimolecular collision complexes in cold molecular clouds happen?
Published in Molecular Physics, 2022
Zhenghai Yang, Srinivas Doddipatla, Chao He, Shane J. Goettl, Ralf I. Kaiser, Ahren W. Jasper, Alexandre C. R. Gomes, Breno R. L. Galvão
The explicit identification of long-lived adducts in the crossed molecular beam reaction of silicon atoms with diacetylene and the implications of these findings to third-body collisions deep inside cold molecular clouds through the exploitation of electronic structure and microcanonical kinetics models have far reaching consequences in understanding the astrochemical evolution of low-temperature interstellar environments. It is believed that radiative association reactions including ion-neutral and neutral-neutral reactions with a typical rate of radiative relaxation of 102–103 s−1 are suggested to dominate in the cold interstellar clouds. The model studies predict that the radiative association reaction of ionised atomic carbon (C+) with molecular hydrogen (H2) initiates a reaction sequence leading to simple hydrocarbons; radiative association reactions involving the methyl ion (CH3+) are thought to be involved in the formation of more complex organic species in denser regions [55–57]. Laboratory studies on the radiative association are especially difficult since it can only occur at very low density and very low temperature. To date, only radiative associations via ion-molecule reaction have been studied experimentally. Gerlich et al. measured the association rates for the ion-neutral systems in the ion traps down to very low temperature of 5 K [16,58,59]. During the reaction, the density dependence of the neutral target gas is measured and the results that association experiments are best performed at densities where stabilisation of the collision complex by a third body collision becomes comparable with radiative stabilisation is revealed. In addition, ion-molecule associative reactions were explored by Armentrout et al. using guided ion beam mass spectrometry, which deepen our understanding of ionic structures and reaction dynamics [60–62]. Here, the conceptual framework of a third-body stabilisation of long-lived collision complexes inside cold molecular clouds suggests that a previously neglected class of chemical reactions – third-body collisions of molecular hydrogen with long-lived reaction intermediates of bimolecular collisions – may influence low-temperature interstellar chemistry. The behaviour of this class of reactions relies on five prerequisites: (i) a barrierless entrance channel from the reactants to the intermediate, (ii) efficient intersystem crossing such as triplet–singlet crossing (non-adiabatic dynamics), (iii) the closure of all exit channels for bimolecular reactions due to reaction endoergicities or energetically insurmountable exit transition states, (iv) re-crossing of the reaction intermediate(s) from the singlet to the triplet surface prior to re-dissociation of the triplet complexes to the initial reactants, and (v) life-time(s) of the reaction intermediate(s) longer than the time between collisions with molecular hydrogen – the dominant molecular component in cold molecular clouds.