In molecular clouds, gaseous species can accrete efficiently on the cold surfaces of dust grains. As for radical-radical reactions, the surface of the grains acts as a third body, and changes dramatically the efficiency of the reactions (i.e., H2 formation), or lowers considerably the barrier to formation (i.e., H2O synthesis) in comparison with gas phase reaction processes. These properties make dust grains efficient catalytic templates. However, the chemical role of dust grains depends on the diffusive properties of the reactive partners. Over the last years, we have developed experimental tools and methods to explore the chemistry occurring on cold (6-50K) surfaces. We have obtained some hints about the diffusivity of H on amorphous ice, and studied in detail the diffusion of O atoms. The latter species appears to have a hopping rate in the range 0.01-100 hops/sec. The diffusion rate of O atoms is dependent on the surface morphology and on the surface temperature. The diffusion law is compatible with a diffusion dominated by quantum tunnelling rather than classical thermal hopping. Using H, O, N atoms and, indirectly, OH and HCO radicals, we have begun to explore many chemical reactive networks. In this presentation, I will focus on the formation of H2O and CO2, and will propose many possible formation routes to obtain these chemical traps. The molecules formed on surfaces have a certain probability of desorbing upon their formation. This non-thermal desorption mechanism, or chemical desorption, has been proposed to explain why some molecules can be detected in the gas phase of those region where they were believed to be part of the icy mantles covering dust grains. We have shown that this process can be very efficient, but is very sensitive to the substrate and the surroundings of the reaction site, is dependent on the kind of molecule formed and its chemical pathway. In my presentation I will present how the surface coverage and the type of reaction can play a major role in the chemical desorption process. I will discuss of possible key parameters that rule this process.

Chemical desorption and diffusive dust chemistry

PIRRONELLO, Valerio;MANICO', Giulio
2014-01-01

Abstract

In molecular clouds, gaseous species can accrete efficiently on the cold surfaces of dust grains. As for radical-radical reactions, the surface of the grains acts as a third body, and changes dramatically the efficiency of the reactions (i.e., H2 formation), or lowers considerably the barrier to formation (i.e., H2O synthesis) in comparison with gas phase reaction processes. These properties make dust grains efficient catalytic templates. However, the chemical role of dust grains depends on the diffusive properties of the reactive partners. Over the last years, we have developed experimental tools and methods to explore the chemistry occurring on cold (6-50K) surfaces. We have obtained some hints about the diffusivity of H on amorphous ice, and studied in detail the diffusion of O atoms. The latter species appears to have a hopping rate in the range 0.01-100 hops/sec. The diffusion rate of O atoms is dependent on the surface morphology and on the surface temperature. The diffusion law is compatible with a diffusion dominated by quantum tunnelling rather than classical thermal hopping. Using H, O, N atoms and, indirectly, OH and HCO radicals, we have begun to explore many chemical reactive networks. In this presentation, I will focus on the formation of H2O and CO2, and will propose many possible formation routes to obtain these chemical traps. The molecules formed on surfaces have a certain probability of desorbing upon their formation. This non-thermal desorption mechanism, or chemical desorption, has been proposed to explain why some molecules can be detected in the gas phase of those region where they were believed to be part of the icy mantles covering dust grains. We have shown that this process can be very efficient, but is very sensitive to the substrate and the surroundings of the reaction site, is dependent on the kind of molecule formed and its chemical pathway. In my presentation I will present how the surface coverage and the type of reaction can play a major role in the chemical desorption process. I will discuss of possible key parameters that rule this process.
File in questo prodotto:
Non ci sono file associati a questo prodotto.

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/20.500.11769/109983
Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus ND
  • ???jsp.display-item.citation.isi??? ND
social impact