122 research outputs found
The reactivity of cyclopropyl cyanide in titan's atmosphere: a possible pre-biotic mechanism
Cyclopropyl cyanide and other simple nitriles detected in Titan's atmosphere could be precursors leading to the formation of organic macromolecules in the atmosphere of Saturn's largest satellite. Proposing a thermodynamically possible mechanism that explains their formation and supports experimental results represents a difficult challenge. Experiments done in the Atomic and Molecular Physics Laboratory at the University of Trento (AMPL) have studied the ion-molecule reaction between cyclopropyl cyanide and its protonated form, with reaction products being characterized by mass spectrometry. In addition to the expected ion-molecule adduct stabilized by non-covalent long-range interactions, in this work we prove that another distinct species having the same mass to charge ratio (m/z) of 135 is also produced. Moreover, from a previous study of the neutral cyclopropyl cyanide potential energy surface (PES) which shows a partial biradical character it has been possible to characterize the formation through the bimolecular reaction of a new covalent cyclic organic molecule. Calculations have been carried out at the ab initio MĂžller-Plesset (MP2) level of theory, ensuring the connectivity of the stationary points by using the intrinsic reaction coordinate (IRC) procedure. In order to characterize the reaction transition state, multireference calculations were done using a complete active space involving six electrons and six molecular orbitals [CAS (6 e, 6 m.o.)]. This study opens the possibility of exploring the formation of new organic molecules by gaseous phase ion-molecule interaction schemes, with such molecules having relevance in interstellar space and in astrobiology (and may be involved in prebiotic molecular evolution)
Ejecta, Dust, and Synchrotron Radiation in B0540-69.3: A More Crab-Like Remnant than the Crab
We present near and mid-infrared observations of the pulsar-wind nebula (PWN)
B0540-69.3 and its associated supernova remnant made with the {\it Spitzer
Space Telescope}. We report detections of the PWN with all four IRAC bands, the
24 m band of MIPS, and the Infrared Spectrograph (IRS). We find no
evidence of IR emission from the X-ray/radio shell surrounding the PWN
resulting from the forward shock of the supernova blast wave. The flux of the
PWN itself is dominated by synchrotron emission at shorter (IRAC) wavelengths,
with a warm dust component longward of 20 m. We show that this dust
continuum can be explained by a small amount (\sim 1-3 \times 10^{-3} \msun)
of dust at a temperature of K, heated by the shock wave generated
by the PWN being driven into the inner edge of the ejecta. This is evidently
dust synthesized in the supernova. We also report the detection of several
lines in the spectrum of the PWN, and present kinematic information about the
PWN as determined from these lines. Kinematics are consistent with previous
optical studies of this object. Line strengths are also broadly consistent with
what one expects from optical line strengths. We find that lines arise from
slow ( km s) shocks driven into oxygen-rich clumps in the shell
swept-up by an iron-nickel bubble, which have a density contrast of relative to the bulk of the ejecta, and that faster shocks (
km s) in the hydrogen envelope are required to heat dust grains to
observed temperatures. We infer from estimates of heavy-element ejecta
abundances that the progenitor star was likely in the range of 20-25 .Comment: 46 pages, 10 figures, accepted for publication in Ap
First absolute measurements of fast-ion losses in the ASDEX Upgrade tokamak
A new diagnostic technique that allows to obtain absolute fluxes of fast-ion losses measured with absolutely calibrated scintillator based fast-ion loss detectors (FILD) is presented here. First absolute fluxes of fast-ion losses have been obtained in the ASDEX Upgrade tokamak. An instrument function that includes the scintillator efficiency, collimator geometry, optical transmission and camera efficiency has been constructed. The scintillator response to deuterium ions in the relevant energy range of fast-ions has been characterized using a tandem accelerator. Absolute flux of neutral beam injection (NBI) prompt losses has been obtained in magnetohydrodynamic quiescent plasmas. The temporal evolution of the heat load measured with FILD follows that measured at the FILD entrance obtained with an Infra-Red camera looking at the FILD detector head. ASCOT simulations are in good agreement with the absolute heat load of NBI prompt losses measured with FILD.Ministerio de EconomĂa, Industria y Competitividad RYC-2011-09152, FIS2015-69362-P, ENE2012-31087EUROfusion Consortium PCIG11-GA-2012- 321455Comunidad Europea de la EnergĂa AtĂłmica 63305
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