S. M. Hurley

The ultrafast dynamics of HBr–water clusters: Influences on ion-pair formation

The ultrafast dynamics of HBr–water clusters have been investigated using pump–probe spectroscopy coupled with reflectron time-of-flight mass spectrometry. HBr clusters, mixed HBr–water clusters, and protonated water clusters are observed in the mass spectra. Dynamic studies reveal that when an HBr chromophore of a cluster with less than five solvent molecules is excited electronically, solvent reorganization occurs to form the solvent separated ion-pair [S. M. Hurley et al., Science 298, 202 (2002)]. The present paper focuses on the influence of clustering on the dynamics of the C and D states of HBr. In addition, further evidence is presented which confirms that complete dissolution of HBr requires five solvent molecules in the isolated species found in complexes comprised of pure water or HBr/H2O mixtures.

Dissociation pathways of sulfur dioxide clusters and mixed sulfur dioxide-water clusters

Abstract A reflectron-time-of-flight mass spectrometer (RTOFMS) coupled with a femtosecond multiphoton ionization technique is used to study the combined metastable and collision-induced dissociation of sulfur dioxide clusters and mixed sulfur dioxide-water clusters. From the dissociation patterns, the general structural arrangement of the clusters is clearly identified: (SO2)m·+ clusters have a SO2·+ core solvated by SO2 molecules; [SO(SO2)n]·+ and [S(SO2)n+1]·+ have a structure of SO·+ · (SO2)n and (SO)2·+ · (SO2)n, respectively. For [HSO2(SO2)]+ clusters, the ion core is HSO2+. H3SO3+ appears to have two isomeric structures: one HSO2+ · H2O, the other H3O+ · SO2.

Dynamics of the E state of HBr and DBr: Evidence for the role of tunneling

The dynamics of the interaction of the Rydberg E(1Σ+) state and the valence state V(1Σ+) of HBr and DBr were investigated using a reflectron time-of-flight mass spectrometer coupled with a femtosecond laser system. Interrogation of the state formed by the avoided crossing of the Rydberg and valence states revealed dynamic behavior that was different for the two isotopes. Pump–probe experiments on HBr showed no change in the lifetime over the range of pump wavelengths of 256.7–254.7 nm. However, the lifetime of DBr decreased as the pump wavelength was tuned bluer. Tunneling is involved in the evolution of the population in photoexcited Rydberg state to the ion-pair state.