SURFRESIDE2: An ultrahigh vacuum system for the investigation of surface reaction routes of interstellar interest

Abstract

A new ultrahigh vacuum experiment is described to study atom and radical addition reactions in interstellar ice analogues for astronomically relevant temperatures. The new setup -SURFace REaction SImulation DEvice (SURFRESIDE 2 ) -allows a systematic investigation of solid state pathways resulting in the formation of molecules of astrophysical interest. The implementation of a double beam line makes it possible to expose deposited ice molecules to different atoms and/or radicals sequentially or at the same time. Special efforts are made to perform experiments under fully controlled laboratory conditions, including precise atom flux determinations, in order to characterize reaction channels quantitatively. In this way, we can compare and combine different surface reaction channels with the aim to unravel the solid state processes at play in space. Results are constrained in situ by means of a Fourier transform infrared spectrometer and a quadrupole mass spectrometer using reflection absorption infrared spectroscopy and temperature programmed desorption, respectively. The performance of the new setup is demonstrated on the example of carbon dioxide formation by comparing the efficiency through two different solid state channels (CO + OH → CO 2 + H and CO + O → CO 2 ) for which different addition products are needed. The potential of SURFRESIDE 2 to study complex molecule formation, including nitrogen containing (prebiotic) compounds, is discussed.

Solid state chemistry of nitrogen oxides – Part II: surface consumption of NO2

“…Here follows a brief description of the setups and the experimental methods, since both systems are discussed in detail elsewhere. 12,15 The use of two ultra-high vacuum (UHV) systems allows for complementary studies of selected interstellar relevant surface reactions. Therefore, a combination of experiments performed in these setups gives information on surface reactions occurring at different surface coverages (sub-monolayer vs. multilayer regime), on different substrates (gold, silicates, graphite, and ASW ice), and in different matrix environments (pure NO and NO 2 , NO in polar ice, and NO and NO 2 in apolar ice).…”

CO2formation on interstellar dust grains: a detailed study of the barrier of the CO + O channel

“…This reaction is relevant to astrochemistry in that it may explain CO 2 formation on interstellar dust grains by surface reactions and thus justifies its abundance in the solid phase. As mentioned in the introduction, the CO + O reaction competes with the CO + OH reaction (some experimental works have already been conducted by Ioppolo et al 2013), another non-energetic route to CO 2 formation in space. The CO + OH pathway seems to be facilitated by the low barrier of the reaction, but it has an other type of hindrance.…”

Atom addition reactions in interstellar ice analogues

“…Calibration methods used so far are based on determining absolute atom densities in the exposing atom beam or, alternatively, on measuring the formation yield of final products in barrierless surface reactions followed by evaluation of original atom flux. Both these methods have been described in detail [125]. Fluxes can be varied by changing the pressure and power settings.…”

“…Very recently, Ioppolo et al [125] directly compared the efficiency of two different carbon dioxide surface formation channels (CO+O and CO+OH) under the same experimental conditions using SURFRESIDE 2 . The use of a double beam line system is essential here and to interpret results from the simultaneous hydrogenation and oxygenation of solid CO, it is necessary to first distinguish the single contributions of the different reaction channels, i.e., O+H, CO+H, and CO+O.…”

“…mainly following CO+OH and CO+O [115][116][117][118][119][120][121][122][123][124][125] The central part of the SURFace REaction Simulation Device (Figure 2) is an UHV chamber (10 -10 -10 -11 mbar) onto which two atom beam lines are mounted that aim at an optically flat gold coated cupper substrate (2.5 x 2.5 cm 2 ) placed in the centre of the main chamber, and mounted on the tip of a cold-head with temperatures accessible between 12 and 300 K using resistive heating. Ices are grown using two all metal high-vacuum stainless steel dosing lines, allowing different gasses to be deposited separately or simultaneously onto the gold substrate.…”