Multiphoton Ionization Mass Spectrum Of Ammonia-alcohol Hydrogen-bonded Cluster

In the past years, the cluster science has brought tremendous advances, especially that of the hydrogen-bonded clusters studies. The hydrogen bond is a weak chemical interaction that plays an important role in many areas of chemistry. Many phenomena such as solvation, energy transfer and chemical reactions are influenced by the hydrogen bond. There are large amounts of hydrogen bond in biological molecules. And proton transfer reaction via the hydrogen bond play an important role in life science. Investigations of hydrogen bonded clusters can provide insight into the process and mechanism of proton transfer.In this work we present the detailed results about the studies of the multiphoton ionization of ammonia-alcohol clusters, which were performed by using a molecular beam, the laser multiphoton ionization and a time-of-flight mass spectrometer as well as ab initio calculations.The mainly results of this paper are as follows:(1) The photoionization process of the ammonia-methanol clusters at 355nm was studied using laser multiphoton ionization and a time-of-flight mass spectrometer. A series of protonated clusters (CH₃OH)_nH⁺ , (CH₃OH)ⁿ(NH₃)H⁺ , (CH₃OH)_n(NH₃)2H⁺ , (CH₃OH)_n(NH₃)₃H⁺ and (CH₃OH)_n(NH₃)₄H⁺ were measured. The log-log plot of laser power intensity and signal intensity indicate that the ionization of the clusters is the ionization of methanol in the clusters. Some possible geometric structures of (CH₃OH)_n(NH₃)_mH⁺ with relatively small sizes were guessed using ab initio calculation method. The structures show that the NH₄⁺ trends as the ion's center, and then it combines with other methanol or ammonia molecule to form the final stable complex cluster ions.(2) In the same experiment condition the multiphoton ionization mass spectrum of ammonia-ethanol clusters were detected at 355nm. A series of clusters (C₂H₅OH)_n,H⁺ , (C₂H₅OH)_n(NH₃)H⁺and (C₂H₅OH)_n(NH³)2H⁺ were detected. The equilibrium conformations of neutral and ionic clusters were obtained using abinitio calculation. The dissociation channels and dissociation energies of both neutral and ionic NH3-C2H5OH clusters were also present. (3) We have investigated the difference among the NH3-CH3O]HL NH3-C2H5OH and NH3-C3H7OH clusters, which showed that the stability of clusters were related with the mono-molecular property.