Application of the position-sensitive photoelectron-photoion-photoion (PSD-PEPIPICO) method to dissociative double-ionization processes in SO 2 , CS 2 , OCS, ICN, CO 2 and N 2 O at photon energies of 40.8 and 48.4 eV provides measurements of total kinetic energy releases and complete descriptions of the kinematics for three-body dissociations of the type ABC → A + B + C. Comparisons of experimental observations with predictions from sequential and concerted bond breaking mechanisms suggest a unified model in which both bonds break on a time scale of ∼100 fs, and electron ejection may be either faster (direct ionization) or competitive (indirect) on this time scale.
An enhanced photoelectron - ion - ion triple coincidence technique eliminates the effect of target molecule thermal velocity on measured ion pair kinetic energy releases. Kinetic energy release distributions at photon energies of 40.8 and 48.4 eV are reported for diatomic molecules and are compared with calculated distributions for direct vertical transitions to theoretically known dication states. Good agreement in the case of indicates that double photoionization of this molecule at 8 eV above threshold is mainly direct. Double photoionization of CO, and NO is purely indirect at the lowest photon energies and has both indirect and direct components at higher energies in this range. The indirect processes give a wide range of final product energies and often involve atomic autoionization. Selectivity in the direct double ionization processes is consistent with the application of symmetry-based propensity rules.
BackgroundThe Deepwater Horizon disaster was the largest marine oil spill in history, and total vertical exposure of oil to the water column suggests it could impact an enormous diversity of ecosystems. The most vulnerable organisms are those encountering these pollutants during their early life stages. Water-soluble components of crude oil and specific polycyclic aromatic hydrocarbons have been shown to cause defects in cardiovascular and craniofacial development in a variety of teleost species, but the developmental origins of these defects have yet to be determined. We have adopted zebrafish, Danio rerio, as a model to test whether water accumulated fractions (WAF) of the Deepwater Horizon oil could impact specific embryonic developmental processes. While not a native species to the Gulf waters, the developmental biology of zebrafish has been well characterized and makes it a powerful model system to reveal the cellular and molecular mechanisms behind Macondo crude toxicity.ResultsWAF of Macondo crude oil sampled during the oil spill was used to treat zebrafish throughout embryonic and larval development. Our results indicate that the Macondo crude oil causes a variety of significant defects in zebrafish embryogenesis, but these defects have specific developmental origins. WAF treatments caused defects in craniofacial development and circulatory function similar to previous reports, but we extend these results to show they are likely derived from an earlier defect in neural crest cell development. Moreover, we demonstrate that exposure to WAFs causes a variety of novel deformations in specific developmental processes, including programmed cell death, locomotor behavior, sensory and motor axon pathfinding, somitogenesis and muscle patterning. Interestingly, the severity of cell death and muscle phenotypes decreased over several months of repeated analysis, which was correlated with a rapid drop-off in the aromatic and alkane hydrocarbon components of the oil.ConclusionsWhether these teratogenic effects are unique to the oil from the Deepwater Horizon oil spill or generalizable for most crude oil types remains to be determined. This work establishes a model for further investigation into the molecular mechanisms behind crude oil mediated deformations. In addition, due to the high conservation of genetic and cellular processes between zebrafish and other vertebrates, our work also provides a platform for more focused assessment of the impact that the Deepwater Horizon oil spill has had on the early life stages of native fish species in the Gulf of Mexico and the Atlantic Ocean.
We use laser photoacoustic spectroscopy to obtain vibrational overtone spectra in the regions of four and five quanta of O-H stretch (4ν OH and 5ν OH ) for gas-phase methyl (MeOOH), ethyl (EtOOH), and tert-butyl hydroperoxide (t-BuOOH). Integrated cross sections for the main peak due to O-H stretch excitation to 4ν OH are similar for all three hydroperoxides (∼2 × 10 -21 cm 2 molecule -1 cm -1 ); cross sections for excitation to and 5ν OH are an order of magnitude smaller. Interpretation of spectral features using a previously reported vibration-torsion model for ROOH molecules, where excitation of torsional motion about the O-O bond accompanies vibrational excitation, yields plausible fits to the spectra. Simulations with the vibration-torsion model and ab initio calculations suggest barriers for torsional motion about the O-O bond to be higher in t-BuOOH than in MeOOH and EtOOH, with a trend of increasing trans torsional barrier height with increasing size of the R group.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.