Desorption Dynamics of Heavy Alkali Metal Atoms (Rb, Cs) off the Surface of Helium Nanodroplets

We present a combined ion imaging and density functional theory study of the dynamics of the desorption process of rubidium and cesium atoms off the surface of helium nanodroplets upon excitation of the perturbed $6s$ and $7s$ states, respectively. Both experimental and theoretical results are well represented by the pseudodiatomic model for effective masses of the helium droplet in the desorption reaction of m_eff/m_He~10 (Rb) and 13 (Cs). Deviations from this model are found for Rb excited to the 6p state. Photoelectron spectra indicate that the dopant-droplet interaction induces relaxation into low-lying electronic states of the desorbed atoms in the course of the ejection process.Comment: in press, J. Phys. Chem. A (2014

Enhanced Ionization of Embedded Clusters by Electron-Transfer-Mediated Decay in Helium Nanodroplets

We report the observation of electron-transfer-mediated decay (ETMD) involving magnesium (Mg) clusters embedded in helium (He) nanodroplets. ETMD is initiated by the ionization of He followed by removal of two electrons from the Mg clusters of which one is transferred to the He ion while the other electron is emitted into the continuum. The process is shown to be the dominant ionization mechanism for embedded clusters for photon energies above the ionization potential of He. For Mg clusters larger than five atoms we observe stable doubly ionized clusters. Thus, ETMD provides an efficient pathway to the formation of doubly ionized cold species in doped nanodroplets

Reconstructing the basal angiosperm phylogeny: evaluating information content of mitochondrial genes

Three mitochondrial (atp1, matR, nad5), four chloroplast (atpB, matK, rbcL, rpoC2), and one nuclear (18S) genes from 162 seed plants, representing all major lineages of gymnosperms and angiosperms, were analyzed together in a supermatrix or in various partitions using likelihood and parsimony methods. The results show that Amborella + Nymphaeales together constitute the first diverging lineage of angiosperms, and that the topology of Amborella alone being sister to all other angiosperms likely represents a local long branch attraction artifact. The monophyly of magnoliids, as well as sister relationships between Magnoliales and Laurales, and between Canellales and Piperales, are all strongly supported. The sister relationship to eudicots of Ceratophyllum is not strongly supported by this study; instead a placement of the genus with Chloranthaceae receives moderate support in the mitochondrial gene analyses. Relationships among magnoliids, monocots, and eudicots remain unresolved. Direct comparisons of analytic results from several data partitions with or without RNA editing sites show that in multigene analyses, RNA editing has no effect on well supported relationships, but minor effect on weakly supported ones. Finally, comparisons of results from separate analyses of mitochondrial and chloroplast genes demonstrate that mitochondrial genes, with overall slower rates of substitution than chloroplast genes, are informative phylogenetic markers, and are particularly suitable for resolving deep relationships.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/147147/1/tax25065680.pd

Desorption Dynamics of Heavy Alkali Metal Atoms (Rb, Cs) Off the Surface of Helium Nanodroplets

We present a combined ion imaging and density functional theory study of the dynamics of the desorption process of rubidium and cesium atoms off the surface of helium nanodroplets upon excitation of the perturbed 6s and 7s states, respectively. Both experimental and theoretical results are well represented by the pseudodiatomic model for effective masses of the helium droplet in the desorption reaction of <i>m</i>_eff/<i>m</i>_He ≈ 10 (Rb) and 13 (Cs). Deviations from this model are found for Rb excited to the 6p state. Photoelectron spectra indicate that the dopant–droplet interaction induces relaxation into low-lying electronic states of the desorbed atoms in the course of the ejection process