H2 formation on Mg-rich amorphous silicates

We present the results of an experimental study on the interaction of D atoms with Mg-rich amorphous silicates. The effects of D irradiation have been analyzed by infrared spectroscopy. The results indicate that HD forms by abstraction of hydrogen atoms chemisorbed in the hydroxyl groups of silicate grains. The formation process occurs for grain and atom temperatures relevant to photodissociation regions

H-atom irradiation of solid state formamide at 12 K

The aim of this work is to understand the stability and investigate the chemical evolution of formamide ice due to thermal hydrogenation at simulated interstellar conditions

Catalytic Role of Refractory Interstellar Grain Analogs on H2 Formation

Refractory dust grains have an important role to play in the chemistry of star and planet-forming regions. Their surfaces interact with interstellar gas and act as a catalyst for the formation of simple and complex molecules in space. Several mechanisms have been invoked to explain how molecular hydrogen is formed in reactions on dust grain surfaces in different regions of space. In this article, we give an overview of our understanding of the laboratory experiments, conducted over the last 20 years, that deal with H2 formation on interstellar grain analogs in space simulated conditions

Lyα Irradiation of Superhydrogenated Coronene Films: Implications for H2 Formation

We present the results of an experimental study of the interaction of Lyα photons with superhydrogenated coronene films. The effects of ultraviolet (UV) irradiation have been analyzed with infrared spectroscopy. The spectral changes provide evidence for UV photodestruction of the C-D bonds of the superhydrogenated coronene with a cross section of 8 ± 2 × 10-20 cm2. The comparison of our experimental result with the prediction from theoretical modeling suggests an extension of the region inside photodissociation regions where superhydrogenated coronene can survive and contribute to H2 formation. H2 formation through abstraction in superhydrogenated coronene dominates over direct H2 loss induced by UV photodestruction

XUV photodesorption of carbon cluster ions and ionic photofragments from a mixed methane–water ice

The photochemical processing of a CH$_4$ : D$_2$O 1 : 3.3 ice mixture adsorbed on an HOPG surface in the XUV regime was investigated using pulses obtained from the Free-electron LASer in Hamburg (FLASH) facility. Ice films were exposed to femtosecond pulses with a photon energy of $hν$ = 40.8 eV, consistent with the HeII resonance line. Cationic species desorbing directly from the ice films were detected using time-of-flight (ToF) mass spectrometry. Simple ions formed through the fragmentation of the parent molecules and subsequent recombination reactions were detected and are consistent with efficient D$^+$ and H$^+$ ejection from the parent species, similar to the case for low energy electron irradiation. The FEL fluence dependencies of these ions are linear or exhibit a non-linear order of up to 3. In addition, a series of Cn$_{n}^+$ cluster ions (with n up to 12) were also identified. These ions display a highly non-linear desorption yield with respect to the FEL fluence, having an order of 6–10, suggesting a complex multi-step process involving the primary products of CH$_4$ fragmentation. Two-pulse correlation measurements were performed to gain further insight into the underlying reaction dynamics of the photo-chemical reactions. The yield of the D$_2$O derived products displayed a different temporal behaviour with respect to the C$_{n}^+$ ions, indicating the presence of very different reaction pathways to the two families of ionic products

XUV photodesorption of carbon cluster ions and ionic photofragments from a mixed methane–water ice

The photochemical processing of a CH$_4$ : D$_2$O 1 : 3.3 ice mixture adsorbed on an HOPG surface in the XUV regime was investigated using pulses obtained from the Free-electron LASer in Hamburg (FLASH) facility. Ice films were exposed to femtosecond pulses with a photon energy of $hν$ = 40.8 eV, consistent with the HeII resonance line. Cationic species desorbing directly from the ice films were detected using time-of-flight (ToF) mass spectrometry. Simple ions formed through the fragmentation of the parent molecules and subsequent recombination reactions were detected and are consistent with efficient D$^+$ and H$^+$ ejection from the parent species, similar to the case for low energy electron irradiation. The FEL fluence dependencies of these ions are linear or exhibit a non-linear order of up to 3. In addition, a series of Cn$_{n}^+$ cluster ions (with n up to 12) were also identified. These ions display a highly non-linear desorption yield with respect to the FEL fluence, having an order of 6–10, suggesting a complex multi-step process involving the primary products of CH$_4$ fragmentation. Two-pulse correlation measurements were performed to gain further insight into the underlying reaction dynamics of the photo-chemical reactions. The yield of the D$_2$O derived products displayed a different temporal behaviour with respect to the C$_{n}^+$ ions, indicating the presence of very different reaction pathways to the two families of ionic products