George M. Daly

Interaction of Zn+ with isobutylene in the gas phase and in clusters. Metal ion induced cationic polymerization

Abstract A variety of closed shell hydrocarbon ions have been observed following charge transfer from Zn+ to isobutylene (C4H8) in a high-pressure mass spectrometric (HPMS) source. The time profiles of these ions and their strong pressure dependence suggest that consecutive and sequential ion-molecule reactions are responsible for their formation. The interaction of Zn+ with isobutylene clusters (C4H8)n generated by a supersonic beam expansion results in efficient generation of the C4H9(C4H8)n+ series. These observations suggest has phase and intracluster polymerization behavior induced by Zn+. Clusters provide a feasible and valuable approach for understanding the mechanism of the early stages of cationic polymerization.

Termolecular proton transfer reactions assisted by ionic hydrogen bond formation: Reactions of aromatic cations with polar molecules

We present a new method that applies resonant‐two‐photon ionization to generate reactant ions selectively in the source of a high‐pressure mass spectrometer (R2PI‐HPMS) for kinetic and equilibrium studies. Applications to reactions that would be obscured otherwise in a complex system are illustrated in mixtures of benzene with polar solvent molecules (S). We observe a novel type of proton transfer reactions from C6H6+• to two S molecules where S=CH3CN, CH3OH, C2H5OH and CH3COOC2H5, and from C6H5CH3+• to two S molecules where S=CH3OH and C2H5OH to form protonated solvent S2H+ dimers. The reactions are driven by the strong hydrogen bonds in the S2H+ dimers and therefore require the formation of the hydrogen bond concertedly with proton transfer, to make the process energetically feasible. The adducts (C6H6+•)S are observed with blocked solvent molecules where the subsequent switching reaction to yield S2H+ is slow, but not with alcohol reactants that can form hydrogen‐bonded chains that facilitate fast subs...

Gas phase clustering of N2 molecules on to TiO+: Comparison with Ti+ and evidence for the octahedral structure of TiO+(N2)5

A striking difference in the clustering efficiency of Ti+ and TiO+ toward N2 or O2 has been observed in a laser vaporization high pressure mass spectrometric source. Evidence for the magic number n=5 within the sequence TiO+(N2)n is presented. The results are consistent with an octahedral structure for TiO+(N2)5.

Polymerization in clusters and in the gas phase using metal ions

Consecutive addition and elimination reactions have been observed following the interaction of Ti+ with isobutylene beam expansion. Clusters provide a feasible and valuable approach for understanding the mechanism of ionic polymerization, and how the size of polymer chains is controlled in such a process.

Proton solvation in ternary clusters of water—methanol—acetonitrile. Evidence for cyclic structures

Abstract The distributions of protonated ternary clusters containing water (W), methanol (M) and acetonitrile (A) have been studied as a function of composition using EI ionization of the ternary cluster beam. The cluster distributions show enhanced ion intensities for the sequence H + W n M m A N +2 indicating solvent shells closing by the blocking groups of acetonitrile molecules. Evidences for cyclic structures in ternary clusters containing five methanol or four water molecules are presented. Cyclic structures in water clusters containing 4–8 molecules are proposed. Implications of the cluster data to the structure of bulk liquid mixtures is discussed. In particular, the cluster model for water—acetonitrile is consistent with the concept of “microheterogeneity” observed in water—acetonitrile liquid mixtures.

Reactions and Thermochemistry of Mixed Cluster Ions

Protonated clusters of the type H+(CH3OH)n(CH3CN)m show a predominant sequence with the composition H+(CH3OH)n(CH3CN)2, where the solvent shells are completed by blocking groups on both ends [4]. Even though ionization involves large excess energies, the observed cluster distributions are sensitive to thermochemical differences as small as 1–3 kcal/mole. Nucleophilic substitution reactions have been observed following the ionization of p-difluorobenzene-methanol mixed clusters. The generation of p-fluoroanisole ion exhibits a strong dependence on the degree of solvation of the cluster. The results for different alcohols will be discussed.