ACS Earth and Space Chemistry最新文献

In interplanetary bodies, organics are found originating from various environments. We replicate the solid-phase conditions in a laboratory to elucidate the step-by-step evolution of organic matter, spanning from dense molecular cloud ices to processes occurring within meteorite parent bodies. The focus of our work is on amino acids, considered as potential chemical tracers of secondary alteration on asteroids. Using gas chromatography and high-resolution mass spectrometry, trace amounts of amino acids are identified in a preaccretional organic analogue formed from a dense molecular ice analogue. This analogue was subsequently exposed to aqueous alteration. This induced an increase in the formation of α- and β-amino acids over time. Supported by high-resolution mass spectrometry data, the reactions involved sugars and amine compounds, followed by amino acid destruction due to the Maillard reaction, which consumes both sugars and amino acids. Surprisingly, a second phase of amino acid formation, specifically α-amino acids, was observed, indicating the potential occurrence of the Strecker reaction. We demonstrate the intricate chemical network occurring within the presence of molecular diversity, similar to what might occur during parent body alteration. Therefore, investigations on reactivity within meteorite parent bodies have to take into account their molecular diversity, recognizing potential cross-reactions, as demonstrated in this work.

Polycyclic aromatic hydrocarbons (PAHs) are abundantly present in the interstellar medium and in our solar system and lock up a significant fraction of cosmic carbon. They are found to be present in interstellar and interplanetary dust particles. Impact ionization mass spectrometers on future space missions can detect such dust particles and assess their composition; it is essential to understand the impact ionization behavior of PAH-based dust particles impinging on metal targets at relevant velocities. To date, impact ionization studies of fast-moving organic-rich dust particles have been limited to vinyl polymers, such as polystyrene or poly(methyl methacrylate). Recently, PAH anthracene has been prepared in the form of microparticles suitable for use in dust accelerators. Here, we present the first comprehensive study of the impact ionization mass spectra of such anthracene microparticles impinging on a gold target at 2–35 km s^–1. The mass spectra recorded for the resulting ionic plasma are strongly dependent on the incident velocity with impacts at 6–10 km s^–1 being optimal for generating distinctive spectral features that enable the identification of the parent molecule. Under these conditions, the protonated parent ion and doubly protonated radical, C₁₄H₁₁⁺, and C₁₄H₁₂^•+ (as well as other diagnostic cluster species such as (C₁₄H₁₀)(CH)⁺ and (C₁₄H₁₁)(C₂H)⁺) can be reproducibly identified. We find that the impact ionization spectra always differ markedly from the electron impact ionization mass spectra reported for anthracene in the literature regardless of the impact velocity. This study highlights the importance of performing fundamental impact ionization studies of organic particles by using a dust accelerator to enable the interpretation of data collected in future space missions.

The adsorption of HCN at the surface of low-density amorphous (LDA) ice and its dissolution in the bulk LDA phase is studied by grand canonical Monte Carlo (GCMC) simulations at the temperatures of 50, 100, and 200 K, characteristic of different domains of the interstellar medium (ISM). Dissolved and adsorbed molecules are distinguished using the identification of the truly interfacial molecules (ITIM) method. The results reveal that the adsorption is monomolecular and the adsorption monolayer is only partially saturated at the point of condensation of HCN. The surface coverage corresponding to the saturated adsorption monolayer is estimated to be 9.8 ± 0.3 μmol/m², providing a better estimate for this quantity than the crude approximation used in evaluating certain experiments. For the entropy of the condensed (glassy) phase of HCN, the simulations provide the value of 17.37 J/(mol K). The adsorption isotherms deviate considerably from the Langmuir shape, revealing that non-negligible interaction occurs between the adsorbed HCN molecules. The adsorption is found to be primarily governed by the dipolar interactions both between the surface water and adsorbed HCN molecules and between HCN neighbors within the adsorption layer. The heat of adsorption at infinitely low surface coverage is estimated to be −49.4 ± 3.9 kJ/mol. Further, the isosteric heat of adsorption at finite coverages is calculated in the entire range of surface coverages. In clear contrast with the adsorption, the dissolution of the HCN molecules remains ideal up to the point of condensation. This indicates that, in spite of the surprisingly large HCN concentrations reached, the HCN–HCN interaction is negligible in the bulk LDA phase. Further, contrary to its adsorption, the dissolution of HCN in LDA ice turns out to be an endothermic process. Finally, our results concerning the adsorption of HCN are not incompatible with the possibility of the oligomerization reaction of the HCN molecules, leading to the prebiotic formation of certain building blocks of biological macromolecules, under interstellar conditions at the LDA surface. Further, assuming that upon approaching the Earth, the transformation of the LDA phase with increasing temperature to liquid water goes through the thermodynamically stable crystalline (I_h) ice phase, which does not dissolve HCN molecules, the presumed expulsion of HCN to the ice surface could provide an additional window of opportunity for their oligomerization.