Origins of Chiral Life in Interstellar Molecular Clouds

The phenomenon of life is discussed within a framework of its origin as defined by the following assumptions. Life, as we know it, is (H-C-N-O) based and relies on the number of bulk (Na-Mg-P-S-Cl-K-Ca) and trace elements (Li-B-F-Si-V-Cr-Mn-Fe-Co-Ni-Cu-Zn-As-Se-Mo-I-W). It originated when the element abundance curve of the living matter and of the universe coincided. By studying the chemical evolution of the solar neighborhood we have obtained the best agreement between the two curves for (4 ± 1)x109 years after the Big Bang. The dust-forming planetary system and stars already contained an excess of L- type amino acids and D- type sugars when incorporated into proteins and primitive organisms. Therefore, the emerging life had to be chiral. Because of the universe's aging, life originated only once.

Isomer-specific kinetics of the C+ + H2O reaction at the temperature of interstellar clouds

The reaction C+ + H2O → HCO+/HOC+ + H is one of the most important astrophysical sources of HOC+ ions, considered a marker for interstellar molecular clouds exposed to intense ultraviolet or x-ray radiation. Despite much study, there is no consensus on rate constants for formation of the formyl ion isomers in this reaction. This is largely due to difficulties in laboratory study of ion-molecule reactions under relevant conditions. Here, we use a novel experimental platform combining a cryogenic buffer-gas beam with an integrated, laser-cooled ion trap and high-resolution time-of-flight mass spectrometer to probe this reaction at the temperature of cold interstellar clouds. We report a reaction rate constant of k = 7.7(6) × 10−9 cm3 s−1 and a branching ratio of formation η = HOC+/HCO+ = 2.1(4). Theoretical calculations suggest that this branching ratio is due to the predominant formation of HOC+ followed by isomerization of products with internal energy over the isomerization barrier.

A chemical dynamics study on the gas phase formation of thioformaldehyde (H2CS) and its thiohydroxycarbene isomer (HCSH)

Complex organosulfur molecules are ubiquitous in interstellar molecular clouds, but their fundamental formation mechanisms have remained largely elusive. These processes are of critical importance in initiating a series of elementary chemical reactions, leading eventually to organosulfur molecules—among them potential precursors to iron-sulfide grains and to astrobiologically important molecules, such as the amino acid cysteine. Here, we reveal through laboratory experiments, electronic-structure theory, quasi-classical trajectory studies, and astrochemical modeling that the organosulfur chemistry can be initiated in star-forming regions via the elementary gas-phase reaction of methylidyne radicals with hydrogen sulfide, leading to thioformaldehyde (H2CS) and its thiohydroxycarbene isomer (HCSH). The facile route to two of the simplest organosulfur molecules via a single-collision event affords persuasive evidence for a likely source of organosulfur molecules in star-forming regions. These fundamental reaction mechanisms are valuable to facilitate an understanding of the origin and evolution of the molecular universe and, in particular, of sulfur in our Galaxy.

The irreplaceable role of ubiquitous cosmic rays in the space chemistry: from the origin of complex species in interstellar molecular clouds to the ozone depletion in the atmospheres of Earth-like planets

A review is given of low-energy cosmic rays (1 MeV-10 GeV), which play an important role in the physics and chemistry of interstellar medium of our Galaxy. According to the generally accepted theory of star formation, cosmic rays penetrate into molecular clouds and ionize the dense gaseous medium of star formation centers besides due to a process of ambipolar diffusion they establish a star formation time scale of about 100-1000 thousand years. The source of cosmic rays in the Galaxy are supernovae remnants where diffusion acceleration at the shock front accelerates particles up to energies of 1015 eV. Being the main source of ionization in the inner regions of molecular clouds, cosmic rays play a fundamental role in the global chemistry of clouds, triggering the entire chain of ion-molecular reactions that make it possible to obtain basic molecules. The review also noted the importance of cosmic rays in atmospheric chemistry: playing a significant role in the formation of nitric oxide, especially with an increase in the flux, they cause a decrease in the concentration of ozone in the atmosphere with all climatic consequences.

Nucleobase synthesis in interstellar ices

The synthesis of nucleobases in natural environments, especially in interstellar molecular clouds, is the focus of a long-standing debate regarding prebiotic chemical evolution. Here we report the simultaneous detection of all three pyrimidine (cytosine, uracil and thymine) and three purine nucleobases (adenine, xanthine and hypoxanthine) in interstellar ice analogues composed of simple molecules including H2O, CO, NH3 and CH3OH after exposure to ultraviolet photons followed by thermal processes, that is, in conditions that simulate the chemical processes accompanying star formation from molecular clouds. Photolysis of primitive gas molecules at 10 K might be one of the key steps in the production of nucleobases. The present results strongly suggest that the evolution from molecular clouds to stars and planets provides a suitable environment for nucleobase synthesis in space.

Water Ice in AGN and Starbursts

Complex chemical species are easier formed in a solid phase, for example in a mixture of ices of water, carbon oxides, methane, ammonia, methanole and other, less abundant molecules. Ultraviolet photons in the range 5 - 13.6 eV and the charged particles with MeV-GeV energies serve as an energy source of reactions. Icy particles containing mentioned substances, can exist only in internal areas of the interstellar molecular clouds protected from influence of external ultraviolet radiation. However cosmic rays are capable to penetrate in clouds and to cause an irradiation of ices by means of secondary ultra-violet photons necessary for initiation of chemical reactions of complexisation. In this work a survivability of ices under harsh conditions of active galaxies is discussed. Preliminary model calculations show that abundances of ices depend not only on ionization parameters of the clouds but also on the shape of incident radiation that is on presence and level of hard ultraviolet and X-ray radiation. The last circumstance is directly related to the radiation of the accretion disk of galaxies with active nuclei and can be used to classify active galaxies, for example to distinguish starburst galaxies from those with active nuclei.