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Große Hoffnungen für mehr Klimaschutz mit dem Green Deal liegen auf Wasserstoff als wichtigem Baustein der Energiewende. Wie kann die Wasserstoffwirtschaft der Zukunft aussehen? Welche Mengen sind erforderlich und welche Infrastrukturen werden benötigt? Wie können in Zukunft nachhaltige Grundstoffe erzeugt werden? Antworten darauf gibt dieser Trendbericht.

The dynamics of the reactions O(3P) + CH₄/CD₄ and O(3P) + cyclo-C₆H₁₂/C₆D₁₂ have been investigated experimentally. Translationally hot O(3P) atoms were generated by laser photolysis of NO₂ at 266 nm. The rotational and fine-structure state distributions in the nascent product OH or OD radicals were determined by laser-induced fluorescence. The deuterium-labelled reactants have provided confirmation of the main features of the product-state partitioning observed previously for normal-hydrogen compounds. Only OH ν' = 0 is detectable from CH₄. CD₄ also produces predominantly OD ν' = 0, with ν' = 1 being just detectable with an estimated branching ratio of ~ 0.06. Both cyclo-C₆H₁₂ and C₆D₁₂ produce significant yields of ν' = 0 and 1 products. Despite the opposite trend in exothermicities, the ν' = 0 products are rotationally hotter from methane than from cyclohexane, indicative of a stereochemical effect. The absolute rotational energy release is in each case found to be essentially independent of hydrogen isotope. It is argued that this supports the accepted collinear abstraction mechanism for this class of reactions. The OH fine-structure state partitioning is not influenced by hydrogen isotope, nor by product vibrational level despite distinct differences in the associated rotational energy release. This appears consistent with a previously derived model involving selected non-adiabatic coupling of adiabatic electronic fine-structure surfaces.

We review the experimental and theoretical work which has been carried out on the dynamics of reactions of O(3P) with saturated hydrocarbons and related systems. We concentrate primarily on gas phase reactions, but also cover in less detail the more limited work on condensed phase and interfacial reactions. Although O(3P) + saturated alkane reactions are the primary focus, the dominant features of their dynamics are compared and contrasted with those of unsaturated alkanes, functionalised alkanes, and inorganic hydrides (including silanes, germanes, H2S, and hydrogen halides). The principal experimental techniques are reviewed. The experimentally determined quantities are identified, including excitation functions, OH rovibrational and fine-structure partitioning, the rather limited equivalent results for the organic radical co-product, and differential cross-sections. The dynamical conclusions that have been inferred are discussed and compared with the predictions of various levels of theory from semi-empirical models through to rigorous ab initio treatments. For many organic systems, most of the evidence points to OH being formed via a direct abstraction mechanism in which the O(3P) atom attacks along an isolated C–H bond. Outstanding problems with this basic interpretation and gaps in the current knowledge base are identified.

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