Matrix Isolation Infrared Spectroscopic And Quantum Chemical Calculations Of The Reactions Of Metal Atoms With Methanol And Acetylene Molecules

The reaction of MO(MO+) + CH4 → CH3OH + M(M+) and its reverse reactionhave gained much attention in providing fundamental information regarding thecatalytic conversion process of CH4 to CH3OH. In this thesis, we reported a combinedmatrix isolation infrared spectroscopic and theoretical study of reactions of metalatoms (M = Be, Mg, Sc and Mn) with CH3OH molecules. On the basis of isotopicsubstitution experiments and theoretical calculations, various reaction intermediatesand products were identified, and reaction mechanisms were discussed. The mainresults are given below. The CH3OH + M reaction paths can be summarized as follows: (2) (1) CH3MOH CH3OH+M M(CH3OH) CH4+MO (3) CH3OMHThe initial step for the CH3OH + M reaction is the formation of the M(CH3OH)complex, which requires no activation energy. From the complex, the metal atomscould insert into the O-H or C-O bond of methanol to form the CH3MOH andCH3OMH intermediates, reactions (2) and (3), which proceed via two differenttransition states. For all the systems reported here, CH3MOH was predicted to bemore stable than CH3OMH. However, the energy barrier for the formation ofCH3OMH (reaction 3) is lower than that for the formation of CH3MOH (reaction 2).The CH3MOH and CH3OMH intermediates could further rearrange to form theCH4OM complex or CH4 + MO. The Mg(CH3OH) and Mn(CH3OH) complexes were experimentally observed, 第 III 页复旦大学博士学位论文which underwent photo-induced isomerization reaction to form CH3MOH orCH3OMH. For Sc and Be, the M(CH3OH) complex are short-lived species, rapidlyrearrange to the thermodynamically less stable CH3OMH molecules, due to the lowenergy barrier for reaction (3). The CH3OScH molecule further rearranged to the CH4OSc complex uponUV-visible irradiation. No such complex or CH4 + MO was observed in the Mg, Beand Mn systems. On the contrary, the CH3MOH or CH3OMH molecule furtherreacted with metal atom to form the dinuclear CH3MOMH molecule. In addition, the reactions of Cr and Sc metal atoms with acetylene were alsoinvestigated using matrix isolation FTIR spectroscopy and theoretical calculations. Insolid argon, ground-state metal atoms reacted with C2H2 to form M(C2H2) (M = Scand Cr) spontaneously on annealing. Theoretical analysis showed that M(C2H2)should not be considered as a metal-C2H2 π?complex but rather as ametalocyclopropene since its C-C bond is a double bond and M-C bond is a singlebond. The M(C2H2) molecule isomerized to the alkynyl hydride HMCCH isomerupon UV-visible irradiation. This isomerization process was predicted to beexothermic but require activation energy. Although the vinylidene MCCH2 isomerwas predicted to be stable species, it was not observed in the experiments. Theoreticalcalculations indicated that the energy barrier for the M(C2H2) → MCCH2 reaction issignificantly higher than that of the M(C2H2) → HMCCH reaction.