Mass spectrometry studies on methane activation and sea salt dissolution in the gas phase: Energetics and mechanics

Both experimental and theoretical sequential association energies of methane molecules to first row transition metal ions (M+) were carried out. It is found that transition metal hydrides (MH+) are able to activate the C-H bond in methane with varying efficiencies. MH⁺+CH4&rlhar2;MCH ⁺3+ H2 NiH+ activates the C-H bond with no energy barrier, and hence the reaction takes place at temperature as low as 80 K. CoH + activates the C-H bond in methane with a 1.9 kcal/mol energy barrier, allowing the reaction to occur at room temperature. FeH+ activates the C-H bond with an energy barrier of 11.3 kcal/mol, therefore the reaction can only be observed at temperatures higher than 600 K. DFT calculations reveal that the electron spin states are changed for all three metal centers during the reactions. Nickel receives the most compensation in energy from the electron spin change, resulting in no energy barrier for the activation of a C-H bond in methane. Cobalt receives less compensation in energy from the electron spin change, resulting in a small energy barrier for the reaction. However, iron needs additional energy to allow the spin change to take place, resulting in a high-energy barrier for the reaction.; In the studies of the microdissolution process of sea salt particles, the sequential association energies of water molecules clustering to Na ₂I+ and Na₃I₂+ are measured. DFT calculations suggest that a significant separation of charge for the Na-I ion pair occurs when four or more water molecules cluster to a single sodium center. Two different solvent-separated ion pairs have been identified with the DFT calculations. For the Na₂I+ system, the dissolution processes—loss of a neutral NaI unit—occurs when six or more water molecules have been added to the salt cluster. For the Na₃I₂+ system, one or two water molecules are able to detach an NaI unit from the salt cluster. The difference in solubility of the Na₂I+ and Na₃I₂ + ions is due to the difference in the energies required to lose an Nat unit from these two species.