Synthesis of complex organic molecules in simulated methane rich astrophysical ices

γ-Ray Driven Aqueous-Phase Methane Conversions into Complex Molecules up to Glycine

Fundamental understanding of initial evolutions of molecules in the universe is of great interest and importance. CH4 is one of the abundant simple molecules in the universe. Herein we report γ-ray, high-energy photons commonly existing in cosmic rays and unstable isotope decay, as an external energy to efficiently drives aqueous-phase CH4 conversions to various products with the presence of oxygen at room temperature. Glycine also forms with an additional introduction of ammonia. Both CH4 conversions and product distributions are modified by solid granules, and a CH3COOH selectivity as high as 82 % is obtained when SiO2 is added. Our results point to γ-ray driven aqueous-phase CH4 conversions as a likely formation network of initial complex organic compounds in the universe and offer an alternative strategy for efficiently utilizing CH4 as the carbon source to produce value-added products at mild conditions, a long-standing challenging task in heterogeneous catalysis.

Mechanisms of Electron-Induced Chemistry in Molecular Ices

Electron-induced chemistry is relevant to many processes that occur when ionizing radiation interacts with matter. This includes radiation damage, curing of polymers, and nanofabrication processes but also the formation of complex molecules in molecular ices grown on dust particles in space. High-energy radiation liberates from such materials an abundance of secondary electrons of which most have energies below 20 eV. These electrons efficiently trigger reactions when they attach to molecules or induce electronic excitation and further ionization. This review focuses on the present state of insight regarding the mechanisms of reactions induced by electrons with energies between 0 and 20 eV that lead to formation of larger products in binary ice layers consisting of small molecules (H2O, CO, CH3OH, NH3, CH4, C2H4, CH3CN, C2H6) or some derivatives thereof (C2H5NH2 and (C2H5)2NH, CH2=CHCH3). It summarizes our approach to identify products and quantify their amounts based on thermal desorption spectrometry (TDS) and electron-stimulated desorption (ESD) experiments performed in ultrahigh vacuum (UHV). The overview of the results demonstrates that, although the initial electron-molecule interaction is a non-thermal process, product formation from the resulting reactive species is often governed by subsequent reactions that follow well-known thermal and radical-driven mechanisms of organic chemistry.

Chemical transformation of molecular ices containing N2O and C2D2 by low energy electrons: New chemical species of astronomical interest

We have employed electron stimulated desorption (ESD) and x-ray photoelectron spectroscopy (XPS) to study the chemical species generated from multilayer films of N₂O, C₂D₂, and mixtures thereof (i.e., N₂O/C₂D₂) by the impact of low energy electrons with energies between 30 and 70 eV. Our ESD results for pure films of N₂O show the production of numerous fragment cations and anions, and of larger molecular ions, of sufficient kinetic energy to escape into vacuum, which are likely formed by ion-molecule scattering in the film. Ion-molecule scattering is also responsible for the production of cations from C₂D₂ films that contain as many as six or seven carbon atoms. Many of the same anions and cations desorb from N₂O/C₂D₂ mixtures, as well as new species, which is the result of ion-molecule scattering in the film. Anion desorption signals further indicate the formation of C-N containing species within the irradiated films. XPS spectra of N1s, C1s, and O1s lines reveal the fragmentation of N-O bonds and gradual formation of molecules containing species containing O-C=O, C=O, and C-O functional groups. A comparison between ESD and XPS findings suggests that species observed in the ESD channel are primarily products of reactions taking place at the film-vacuum interface, while those observed in the XPS derive from reactions occurring within the solid.

A hitherto unknown stability of DNA basepairs

The resonance capture of ubiquitous very low energy electrons (vLEEs) into the π* orbitals of nucleobases is a potential doorway to DNA damage. Our ab initio quantum chemical calculations reveal a possible protection function, which is specific to the complementary basepairing, against such vLEE induced DNA damage.

Ab initio Molecular Dynamics Simulation Study of Dissociation Electron Attachment to Lactic Acid and Isomer

Dissociation processes of lactic acid and its isomer formed by low-energy dissociation electron attachment (DEA) in the gas phase are investigated by using ab initio molecular dynamics (MD) simulations. The ab initio MD simulations using an atom-centered density matrix propagation (ADMP) method are carried out to investigate the DEA dissociation process of lactic acid and its isomer. The analysis of the simulated dissociation trajectories of lactic acid and its isomer indicates that the C-C, C-H, and C-O bonds are cleaved within femtoseconds of the simulation time scale in the DEA dissociation process, and the difference in dissociation trajectory depends on the size of the three basis sets. The simulation results enable us to gain insights into the DEA dissociation process of lactic acid and its isomer. In this work, we present a comparative study of the 6-31 + G(d,p), 6-311++G(2d,2p), and Aug-cc-pVDZ basis sets of the DEA dissociation simulation of lactic acid and its isomer. The comparative study results indicate that the 6-311++G(2d,2p) is an excellent basis set for the ADMP trajectory simulation of lactic acid and its isomer in the DEA dissociation process. The natural bond orbital (NBO) analysis is carried out to characterize variation in the charge population and charge transfer accompanied by the C-C, C-H, and C-O bond dissociation processes for lactic acid and its isomer in the ADMP trajectory simulation. ADMP simulation and NBO analysis of the dissociation trajectory is considered an important initial and decisive step in DEA dissociation dynamics for lactic acid and its isomer.

Low energy (1-19 eV) electron scattering from condensed thymidine (dT) I: absolute vibrational excitation cross sections

Absolute cross sections (CSs) for vibrational excitation by electrons of energy between 1-19 eV scattering from condensed thymidine (dT) were measured by means of high-resolution electron energy loss spectroscopy (HREELS). The CSs were extracted from electron energy loss spectra of dT condensed on multilayers film of Ar held at about 20 K under ultra-high vacuum (∼1 × 10-11 Torr). dT is one of the most complex molecules to be studied in condensed phase by HREELS. The magnitudes of the vibrational CSs lie within the 10-17 cm2 range. Structures observed in the energy dependence of the vibrational CSs under 3 eV and around 4 eV were compared with previous results of gas- and solid-phase studies on dT and related molecules (e.g., thymine and tetrahydrofuran). These structures were attributed to the formation of shape resonances.

Origin of alkylphosphonic acids in the interstellar medium

For decades, the source of phosphorus incorporated into Earth's first organisms has remained a fundamental, unsolved puzzle. Although contemporary biomolecules incorporate P(+V) in their phosphate moieties, the limited bioavailability of phosphates led to the proposal that more soluble P(+III) compounds served as the initial source of phosphorus. Here, we report via laboratory simulation experiments that the three simplest alkylphosphonic acids, soluble organic phosphorus P(+III) compounds, can be efficiently generated in interstellar, phosphine-doped ices through interaction with galactic cosmic rays. This discovery opens a previously overlooked avenue into the formation of key molecules of astrobiological significance and untangles basic mechanisms of a facile synthesis of phosphorus-containing organics in extraterrestrial ices, which can be incorporated into comets and asteroids before their delivery and detection on Earth such as in the Murchison meteorite.

Electron-induced origins of prebiotic building blocks of sugars: mechanism of self-reactions of a methanol anion dimer

Reactions of methanol dimers in interstellar medium driven by low energy irradiation may lead to prebiotic precursors.