Density functional and multiphoton ionization studies of N, N-dimethylformamide–(methanol) n clusters

Abstract

The multiphoton ionization of the hydrogen-bonded clusters N, N-dimethylformamide–(methanol) n (DMF–(CH 3OH) n ) was studied using a time-of-flight mass spectrometer at the wavelengths of 355 and 532 nm. At both wavelengths, a series of protonated DMF–(CH 3OH) n H + ions was obtained. The clusters were also investigated by density functional theory B3LYP method in conjunction with basis sets 6-31+G(d,p) and 6-311+G(2d,p). Equilibrium geometries of both neutral and ionic DMF–CH 3OH clusters, and dissociation channels and dissociation energies of the ionic clusters are presented. The results show that when DMF–CH 3OH is vertically ionized and dissociated, DMFH + and CH 3O are the dominant products via proton transfer reaction. A high energy barrier makes another channel corresponding to the production of DMFH + and CH 2OH disfavored. In the DMF–(CH 3OH)H + ion, the proton prefers to link with the O atom of DMF molecule. Variation of atomic charges during proton transfer in hydrogen bond of the protonated cluster DMF–(CH 3OH)H + ion is also discussed.