A new ultra-high vacuum experiment is described that allows studying photo-induced chemical processes in interstellar ice analogues. MATRI2CES - a Mass Analytical Tool to study Reactions in... Show moreA new ultra-high vacuum experiment is described that allows studying photo-induced chemical processes in interstellar ice analogues. MATRI2CES - a Mass Analytical Tool to study Reactions in Interstellar ICES applies a new concept by combining laser desorption and time-of-flight mass spectrometry with the ultimate goal to characterize in situ and in real time the solid state evolution of organic compounds upon UV photolysis for astronomically relevant ice mixtures and temperatures. The performance of the experimental setup is demonstrated by the kinetic analysis of the different photoproducts of pure methane (CH4) ice at 20 K. A quantitative approach provides formation yields of several new species with up to four carbon atoms. Convincing evidence is found for the formation of even larger species. Typical mass resolutions obtained range from M/M ∼320 to ∼400 for CH4 and argon, respectively. Additional tests show that the typical detection limit (in monolayers) is ≤0.02 ML, substantially more sensitive than the regular techniques used to investigate chemical processes in interstellar ices. Show less
The cyclopropenyl cation (c-C3H3 +) is the smallest aromatic hydrocarbon molecule and considered to be a pivotal intermediate in ion–molecule reactions in space. An astronomical identification has... Show moreThe cyclopropenyl cation (c-C3H3 +) is the smallest aromatic hydrocarbon molecule and considered to be a pivotal intermediate in ion–molecule reactions in space. An astronomical identification has been prohibited so far, because of a lack of gas-phase data. Here we report the first high resolution infrared laboratory gas-phase spectrum of the ν4 (C–H asymmetric stretching) fundamental band of c-C3H3 +. The c-C3H3 + cations are generated in supersonically expanding planar plasma by discharging a propyne/helium gas pulse, yielding a rotational temperature of ∼35 K. The absorption spectrum is recorded in the 3.19μm region using sensitive continuous-wave cavity ring-down spectroscopy. The analysis of about 130 ro-vibrational transitions results in precise spectroscopic parameters. These constants allow for an accurate comparison with high-level theoretical predictions, and provide the relevant information needed to search for this astrochemically relevant carbo-cation in space. Show less
Bossa, J.B.; Isokoski, K.; Paardekooper, D.M.; Bonnin, M; Linden, E van der; Triemstra, T; ... ; Linnartz, H.V.J. 2014
Ultraviolet (UV) ice photodesorption is an important non-thermal desorption pathway in many interstellar environments that has been invoked to explain observations of cold molecules in disks,... Show moreUltraviolet (UV) ice photodesorption is an important non-thermal desorption pathway in many interstellar environments that has been invoked to explain observations of cold molecules in disks, clouds, and cloud cores. Systematic laboratory studies of the photodesorption rates, between 7 and 14 eV, from CO:N$_{2}$ binary ices, have been performed at the DESIRS vacuum UV beamline of the synchrotron facility SOLEIL. The photodesorption spectral analysis demonstrates that the photodesorption process is indirect, i.e., the desorption is induced by a photon absorption in sub-surface molecular layers, while only surface molecules are actually desorbing. The photodesorption spectra of CO and N$_{2}$ in binary ices therefore depend on the absorption spectra of the dominant species in the sub-surface ice layer, which implies that the photodesorption efficiency and energy dependence are dramatically different for mixed and layered ices compared with pure ices. In particular, a thin (1-2 ML) N$_{2}$ ice layer on top of CO will effectively quench CO photodesorption, while enhancing N$_{2}$ photodesorption by a factor of a few (compared with the pure ices) when the ice is exposed to a typical dark cloud UV field, which may help to explain the different distributions of CO and N$_{2}$H$^{+}$ in molecular cloud cores. This indirect photodesorption mechanism may also explain observations of small amounts of complex organics in cold interstellar environments. Show less
Context. The {$ν$}$_{2}$ bending mode of pure CO$_{2}$ ice around 15.2 {$μ$}m exhibits a fine double-peak structure that offers a sensitive probe to study the physical and chemical properties of... Show moreContext. The {$ν$}$_{2}$ bending mode of pure CO$_{2}$ ice around 15.2 {$μ$}m exhibits a fine double-peak structure that offers a sensitive probe to study the physical and chemical properties of solid CO$_{2}$ in space. Current laboratory spectra do not fully resolve the CO$_{2}$ ice features. Aims: To improve the fitting of the observed CO$_{2}$ features, high-resolution solid-state infrared spectra of pure CO$_{2}$ ice are recorded in the laboratory for a series of astronomically relevant temperatures and at an unprecedented level of detail. Methods: The infrared spectra of pure CO$_{2}$ ice were recorded in the 4000 to 400 cm$^{-1}$ (2.5-25 {$μ$}m) region at a resolution of 0.1 cm$^{-1}$ using Fourier transform infrared spectroscopy. Results: Accurate band positions and band widths (FWHM) of pure CO$_{2}$ ice are presented for temperatures of 15, 30, 45, 60, and 75 K. The focus of this spectroscopic work is on the CO$_{2}$ ({$ν$}$_{2}$) bending mode, but more accurate data are also reported for the $^{12}$CO$_{2}$ and $^{13}$CO$_{2}$ ({$ν$}$_{3}$) stretching mode, and CO$_{2}$ ({$ν$}$_{1}$+{$ν$}$_{3}$) and (2{$ν$}$_{2}$+{$ν$}$_{3}$) combination bands. FITS files of the spectra are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/555/A85Show less
We report the detection of a unique CO$_{2}$ ice band toward the deeply embedded, low-mass protostar HOPS-68. Our spectrum, obtained with the Infrared Spectrograph on board the Spitzer Space... Show moreWe report the detection of a unique CO$_{2}$ ice band toward the deeply embedded, low-mass protostar HOPS-68. Our spectrum, obtained with the Infrared Spectrograph on board the Spitzer Space Telescope, reveals a 15.2 {$μ$}m CO$_{2}$ ice bending mode profile that cannot be modeled with the same ice structure typically found toward other protostars. We develop a modified CO$_{2}$ ice profile decomposition, including the addition of new high-quality laboratory spectra of pure, crystalline CO$_{2}$ ice. Using this model, we find that 87%-92% of the CO$_{2}$ is sequestered as spherical, CO$_{2}$-rich mantles, while typical interstellar ices show evidence of irregularly shaped, hydrogen-rich mantles. We propose that (1) the nearly complete absence of unprocessed ices along the line of sight is due to the flattened envelope structure of HOPS-68, which lacks cold absorbing material in its outer envelope, and possesses an extreme concentration of material within its inner (10 AU) envelope region and (2) an energetic event led to the evaporation of inner envelope ices, followed by cooling and re-condensation, explaining the sequestration of spherical, CO$_{2}$ ice mantles in a hydrogen-poor mixture. The mechanism responsible for the sublimation could be either a transient accretion event or shocks in the interaction region between the protostellar outflow and envelope. The proposed scenario is consistent with the rarity of the observed CO$_{2}$ ice profile, the formation of nearly pure CO$_{2}$ ice, and the production of spherical ice mantles. HOPS-68 may therefore provide a unique window into the protostellar feedback process, as outflows and heating shape the physical and chemical structure of protostellar envelopes and molecular clouds. Show less
Bertin, M.; Fayolle, E.; Romanzin, C.; Poderoso, H.; Michaut, X.; Philippe, L.; ... ; Fillion, J. 2013
Ultraviolet (UV) ice photodesorption is an important non-thermal desorption pathway in many interstellar environments that has been invoked to explain observations of cold molecules in disks,... Show moreUltraviolet (UV) ice photodesorption is an important non-thermal desorption pathway in many interstellar environments that has been invoked to explain observations of cold molecules in disks, clouds, and cloud cores. Systematic laboratory studies of the photodesorption rates, between 7 and 14 eV, from CO:N$_{2}$ binary ices, have been performed at the DESIRS vacuum UV beamline of the synchrotron facility SOLEIL. The photodesorption spectral analysis demonstrates that the photodesorption process is indirect, i.e., the desorption is induced by a photon absorption in sub-surface molecular layers, while only surface molecules are actually desorbing. The photodesorption spectra of CO and N$_{2}$ in binary ices therefore depend on the absorption spectra of the dominant species in the sub-surface ice layer, which implies that the photodesorption efficiency and energy dependence are dramatically different for mixed and layered ices compared with pure ices. In particular, a thin (1-2 ML) N$_{2}$ ice layer on top of CO will effectively quench CO photodesorption, while enhancing N$_{2}$ photodesorption by a factor of a few (compared with the pure ices) when the ice is exposed to a typical dark cloud UV field, which may help to explain the different distributions of CO and N$_{2}$H$^{+}$ in molecular cloud cores. This indirect photodesorption mechanism may also explain observations of small amounts of complex organics in cold interstellar environments. Show less
Context. Ultraviolet photodesorption of molecules from icy interstellar grains can explain observations of cold gas in regions where thermal desorption is negligible. This non-thermal desorption... Show moreContext. Ultraviolet photodesorption of molecules from icy interstellar grains can explain observations of cold gas in regions where thermal desorption is negligible. This non-thermal desorption mechanism should be especially important where UV fluxes are high. Aims: N$_{2}$ and O$_{2}$ are expected to play key roles in astrochemical reaction networks, both in the solid state and in the gas phase. Measurements of the wavelength-dependent photodesorption rates of these two infrared-inactive molecules provide astronomical and physical-chemical insights into the conditions required for their photodesorption. Methods: Tunable radiation from the DESIRS beamline at the SOLEIL synchrotron in the astrophysically relevant 7 to 13.6 eV range is used to irradiate pure N$_{2}$ and O$_{2}$ thin ice films. Photodesorption of molecules is monitored through quadrupole mass spectrometry. Absolute rates are calculated by using the well-calibrated CO photodesorption rates. Strategic N$_{2}$ and O$_{2}$ isotopolog mixtures are used to investigate the importance of dissociation upon irradiation. Results: N$_{2}$ photodesorption mainly occurs through excitation of the b$^{1}${$Pi$}$_u$ state and subsequent desorption of surface molecules. The observed vibronic structure in the N$_{2}$ photodesorption spectrum, together with the absence of N$_{3}$ formation, supports that the photodesorption mechanism of N$_{2}$ is similar to CO, i.e., an indirect DIET (Desorption Induced by Electronic Transition) process without dissociation of the desorbing molecule. In contrast, O$_{2}$ photodesorption in the 7-13.6 eV range occurs through dissociation and presents no vibrational structure. Conclusions: Photodesorption rates of N$_{2}$ and O$_{2}$ integrated over the far-UV field from various star-forming environments are lower than for CO. Rates vary between 10$^{-3}$ and 10$^{-2}$ photodesorbed molecules per incoming photon. Show less
