The vibrationally resolved spectra of the pyrene cation and doubly-dehydrogenated pyrene cation(C16H10+; Py+ and C16H8+; ddPy+) are presented. Infrared predissociation spectroscopy is employed... Show moreThe vibrationally resolved spectra of the pyrene cation and doubly-dehydrogenated pyrene cation(C16H10+; Py+ and C16H8+; ddPy+) are presented. Infrared predissociation spectroscopy is employed tomeasure the vibrational spectrum of both species using a cryogenically cooled 22-pole ion trap. Thespectrum of Py+ allows a detailed comparison with harmonic and anharmonic density functional theory(DFT) calculated normal mode frequencies. The spectrum of ddPy+ is dominated by absorption featuresfrom two isomers (4,5-ddPy+ and 1,2-ddPy+) with, at most, minor contributions from other isomers.These findings can be extended to explore the release of hydrogen from interstellar PAH species. Ourresults suggest that this process favours the loss of adjacent hydrogen atoms. Show less
EX Lup is the prototype of a class of pre-main-sequence eruptive stars defined by their repetitive outbursts lasting several months. In 2008 January-September EX.Lup underwent its historically... Show moreEX Lup is the prototype of a class of pre-main-sequence eruptive stars defined by their repetitive outbursts lasting several months. In 2008 January-September EX.Lup underwent its historically largest outburst, brightening by about 4 mag in visual light. In previous studies we discovered ongoing silicate crystal formation in the inner disk during the outburst, but also noticed that the measured crystallinity fraction started decreasing after the source returned to the quiescent phase. Here we present new observations of the 10 mu m silicate feature, obtained with the MIDI and VISIR instruments at Paranal Observatory. The observations demonstrate that within five years practically all crystalline forsterite disappeared from the surface of the inner disk. We reconstruct this process by presenting a series of parametric axisymmetric radiative transfer models of an expanding dust cloud that transports the crystals from the terrestrial zone to outer disk regions where comets are supposed to form. It is possible the early Sun also experienced similar flare-ups, and the forming planetesimals might have incorporated crystalline silicate material produced by such outbursts. Finally, we discuss how far the location of the dust cloud could be constrained by future James Webb Space Telescope observations. Show less
Wilkinson, M.D.; Dumontier, M.; Aalbersberg, I.J.; Appleton, G.; Axton, M.; Baak, A.; ... ; Mons, B. 2019
A structural characterization of the products formed in the dissociative electron ionization of adamantane (C10H16) is presented. Molecular structures of product ions are suggested based on... Show moreA structural characterization of the products formed in the dissociative electron ionization of adamantane (C10H16) is presented. Molecular structures of product ions are suggested based on multiple‐photon dissociation spectroscopy using the Free Electron Laser for Infrared eXperiments (FELIX) in combination with quantum‐chemical calculations. Product ions are individually isolated in an ion trap tandem mass spectrometer and their action IR spectra are recorded. Atomic hydrogen loss from adamantane yields the 1‐adamantyl isomer. The IR spectrum of the C8H11+ product ion is best reproduced by computed spectra of 2‐ and 4‐protonated meta‐xylene and ortho‐ and para‐protonated ethylbenzenes. The spectrum of the product ion at m/z 93 suggests that it is composed of a mixture of ortho‐protonated toluene, para‐protonated toluene and 1,2‐dihydrotropylium, while the spectrum of the m/z 79 ion is consistent with the benzenium ion. This study thus suggests that adamantane is efficiently converted into aromatic species and astrophysical implications for the interstellar medium are highlighted. Show less
A solid understanding of and a reliable model for the formation pathways of polycyclic aromatic (nitrogen containing) hydrocarbons (PA(N)Hs) is needed to account for their abundance in the... Show moreA solid understanding of and a reliable model for the formation pathways of polycyclic aromatic (nitrogen containing) hydrocarbons (PA(N)Hs) is needed to account for their abundance in the interstellar medium and in Titan's atmosphere as well as to mitigate the emission of these carcinogens in our terrestrial environment. We have investigated the phenyl + acrylonitrile reaction mechanism between 600 and 1200 K in a hot microreactor. Radical intermediates (C9H8N˙), formed by addition, and closed-shell C9H7N products, formed by subsequent hydrogen elimination, are isomer-selectively identified using photoion mass-selected threshold photoelectron spectroscopy in conjunction with Franck–Condon simulations. Although quinoline is the most stable product, the calculated potential energy surface and a kinetic model confirm that the reaction is kinetically controlled and yields four open-chain isomers instead. The absence of quinoline is in stark contrast with the isoelectronic phenyl + vinylacetylene reaction that produces naphthalene. Ab initio calculations suggest that this change is brought about by the stability of the nitrile group, which inhibits ring formation. Therefore, it is unlikely that nitrile precursors form nitrogen-containing rings, which calls for alternative pathways by which nitrogen atoms can be incorporated in aromatic systems to explain their presence in the ISM and Titan's atmosphere Show less
Kofman, V.; Witlox, M.J.A.; Bouwman, J.; Kate, L. ten; Linnartz, H. 2018
