Theoretical investigation of the interaction of CH(4) with Al(2) and Al(3) neutral and charged clusters.
We have studied the interaction of CH(4) with Al(2) and Al(3) neutral and charged clusters in the two lowest lying spin states using density functional theory. These calculations, via extended search, are used to determine the stable positions of H and CH(3) near the cluster, and the transition state to break the H-CH(3) bond. In all cases, stable methyl-aluminum-hydrides are possible. The H desorption is studied by means of vibration analysis and application of transition state theory. A common observed trend is that, in breaking the H-CH(3) bond, the interacting H atom is attached to the "surface" of the clusters attracting some negative charge of approximately 0.2e. The charge transfer is illustrated using the corresponding orbitals near the transition state in conjunction with the computed Mulliken population analysis. Thermal vibrations, generally, do not enhance the reaction. In all exothermic cases, the binding energy toward CH(3)+HAl(n) (charge) increases with increasing charge of the original Al(n) ((q=-1,0,1)) cluster. Although Al lacks occupied d-orbitals, the small Al clusters reduce the (free methane) CH(3)-H dissociation barrier except for Al(3) ((q=-1,0)). The relevant reactions in desorption require approximately 400-700 degrees C.
Alexandrou
E I
EI
Theoretical and Physical Chemistry Institute, National Hellenic Research Foundation, Athens 11635, Greece.
Gross
A
A
Bacalis
N C
NC
D000535:Aluminum / Q000737:chemistry*; D003198:Computer Simulation; D008697:Methane / Q000737:chemistry*; D011789:Quantum Theory; D055672:Static Electricity
D000535:Aluminum; D008697:Methane