Stephan Schlemmer

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Recent observations of H 2 and H + 3 in diffuse interstellar sightlines revealed a difference in the nuclear spin excitation temperatures of the two species. This discrepancy comes as a surprise, as H + 3 and H 2 should undergo frequent thermalizing collisions in molecular clouds. Non-thermal behavior of the fundamental H + 3 /H 2 collision system at low(More)
At the high densities and low temperatures found in star forming regions, all molecules other than H 2 should stick on dust grains on timescales shorter than the cloud lifetimes. Yet these clouds are detected in the millimeter lines of gaseous CO. At these temperatures, thermal desorption is negligible and hence a non-thermal desorption mechanism is(More)
We present laboratory data on pure, layered and mixed CO and O2 ices relevant for understanding the absence of gaseous O2 in space. Experiments have been performed on interstellar ice analogues under ultra high vacuum conditions by molecular deposition at 14 K on a gold surface. A combination of reflection absorption infrared spectroscopy (RAIRS) and(More)
Protonation of methane (CH4), a rather rigid molecule well described by quantum mechanics, produces CH5(+), a prototypical floppy molecule that has eluded definitive spectroscopic description. Experimental measurement of high-resolution spectra of pure CH5(+) samples poses a formidable challenge. By applying two types of action spectroscopy predicated on(More)
  • Sandra Brünken, Olli Sipilä, Edward T Chambers, Jorma Harju, Paola Caselli, Oskar Asvany +5 others
  • 2014
The age of dense interstellar cloud cores, where stars and planets form, is a crucial parameter in star formation and difficult to measure. Some models predict rapid collapse, whereas others predict timescales of more than one million years (ref. 3). One possible approach to determining the age is through chemical changes as cloud contraction occurs, in(More)
astrochemistry · hydrogen · kinetics · laser chemistry The chemistry of the early universe is seemingly simple since it involves only hydrogen and helium in various forms. The first stars formed out of this primordial gas after the " dark ages " several hundred million years after the Big Bang. How this happened in detail is one of the most exciting(More)
Protonated methane, CH5+, continues to elude definitive structural assignment, as large-amplitude vibrations and hydrogen scrambling challenge both theory and experiment. Here, the infrared spectrum of bare CH5+ is presented, as detected by reaction with carbon dioxide gas after resonant excitation by the free electron laser at the FELIX facility in the(More)
Single-photon infrared emission spectroscopy (SPIRES) has been used to measure emission spectra from polycyclic aromatic hydrocarbons (PAHs). A supersonic free-jet expansion has been used to provide emission spectra of rotationally cold and vibrationally excited naphthalene and benzene. Under these conditions, the observed width of the 3.3-micrometers (C-H(More)
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