Cluster anions in the gas-phase: Time-of-flight mass spectrometry and photoelectron spectroscopic studies.

摘要

Time-of-flight (TOF) mass spectrometry and photoelectron spectroscopy (PES) have been used to analyze the negative ions in the gas-phase. Various types of ion sources were used to generate the ions in the experiment. Here in this thesis, three topics were discussed: (1) aluminum hydride cluster anions, (2) transition metal-organic cluster anions and (3) biomolecule anions. By comparing with the theoretical calculations, the structures, electronic properties and potential applications of the cluster anions as well as their corresponding neutrals were revealed. (1) Aluminum hydrides were not studied as thoroughly as their analogs, boron hydrides (boranes) until a pulsed arc cluster ion source (PACIS) was developed in our lab. Hundreds of previously unobserved aluminum hydride cluster anions were synthesized in the gas-phase. Among these clusters, many interesting and important ones were studied. For example, closo-alane, AlnHn+2 (n=4-8) neutrals were found to be especially stable with n=4 to be the most stable one; Al nH3n+i- (n=4-8) anions were found to be polymeric chain-like structures. These clusters could be potentially made in the condensed phase as novel energetic materials. Our study opened a new chapter of aluminum hydride chemistry. (2) Transition metal-organic complexes were believed to be possibly retaining the high magnetic moment of the transition metal clusters at their reduced sizes. It is known that the magnetic moments are much lower in the condensed phase of the same transition metals. We attached different organic species to Fe, and Co atoms or clusters. From the comparison between the PES spectra and the calculation, the magnetic moment for each complex could be roughly determined. The compounds that could retain the high magnetic moments are potential building blocks of magnetic materials. (3) Techniques were developed to generate biomolecules (nucleobases, base pairs, hydrated nucleosides and a peptide were discussed in this thesis) in the gas-phase. We were able to, unlike other methods usually causing fragmentation problem, produce parent anions of the biomolecules. Information from the photoelectron spectroscopic studies could benefit the understanding of DNA damage, hydration of DNA, and medication et al.