Experiments and Calculations on Photoionization and Dissociative Photoionization of CH2CO

The dissociative photoionization of molecular‐beam cooled CH₂CO in a region of ?10–20 eV was investigated with photoionization mass spectrometry using a synchrotron radiation as the light source. Photoionization efficiency curves of CH₂CO⁺ and of observed fragment ions CH₂⁺, CHCO⁺, HCO⁺, C₂O⁺, CO⁺, and C₂H₂⁺ were measured to determine their appearance energies. Relative branching ratios as a function of photon energy were determined. Energies for formation of these observed fragment ions and their neutral counterparts upon ionization of CH₂CO are computed with the Gaussian‐3 method. Dissociative photoionization channels associated with six observed fragment ions are proposed based on comparison of determined appearance energies and predicted energies. The principal dissociative processes are direct breaking of C=C and C‐H bonds to form CH₂⁺ + CO and CHCO⁺ + H, respectively; at greater energies, dissociation involving H migration takes place.     

Transformation of Metallic Ti to TiH2 Phase in the Ti/MgH2 Composite and Its Influence on the Hydrogen Storage Behavior of MgH2

The current work explores the in-situ formation of TiH₂ additive in a Ti/MgH₂ nanocomposite system. Mild mechanical milling leaves Ti chemically unchanged, while formation of stable TiH_2–x occurs upon strong mechanical milling. TiH_2–x further transforms to TiH₂ upon recycling the powder (dehydrogenation and subsequent hydrogenation) and lowers the activation energy of MgH₂ to 89.4 kJ (mol H₂)⁻¹ [E_a of as-received MgH₂ is 153 kJ (mol H₂)⁻¹]. This work also reiterates that metallic Ti additive mixed MgH₂ requires strong mechanical milling for better H₂ ab/de-sorption performance. The current observations support the view that lattice strain may be an important factor in the catalysis of additives incorporated MgH₂ hydrogen storage systems.