Ultra-low-temperature reactions of C and Si atoms inside superfluid helium nanodroplets
Final Report Abstract
The studies performed in the frame of the current project show an extremely high reactivity of C atoms. The C atoms are found to react at T = 0.37 K almost with all studied molecules. The only found exception is adamantane. This shows an absence of an energy barrier in the entrance channel for all reactions and assures their high rates at any low-temperature that can be found in nature. In most cases the reactions of C atoms leads to the formations of organic radicals, which are often formed in the long-lived electronically excited states. In the case of the surface reactions, they can immediately react further forming large organic and biological molecules. Therefore, the obtained results suggest that in the interstellar medium the conversion of the carbon from atomic to the molecular form would lead to the formation of large quantities of biologically relevant molecules, which can later be delivered to planets facilitating the formation of the biopolymers. In current project we have developed quantitate calorimetric method, which can be used to measure the energy released in reactions of a single pair of reactants. These data can be directly compared with the results of quantum chemical computations leading to unequivocal conclusions regarding the reaction pathways and the presence of energy barriers. Due to the presence of the third body in the experiment, the obtained results are much more suitable for the prediction of the outcome of the chemical surface reactions compared to the results of the gas-phase studies. The new method was applied to study the reactions of C atoms with H2, O2, C2H2, CO2, and NH3. In all cases the barrierless reactions of C atoms with molecules were found. The investigated reactions are expected to have an important role in astrochemistry and should be considered in the models of the chemistry of dense regions of the ISM. The interesting finding in these studies is that the formed products of chemical reactions are often formed in long-lived excited states. Therefore, in the case of the surface reaction the excited products can directly react with neighboring molecules. The experimental investigation of the condensation of carbon in liquid helium confirms the high reactivity of C atoms and C3 molecules and reveals the formation of the organic carbon. It also demonstrates an efficient inclusion of oxygen and hydrogen elements, which were present in the forms of H2, H2O, and CO molecules to the final condensate. These data suggest that inclusion of other abundant elements (e.g. N, S, etc.) present in the gas phase during condensation of the carbon should be efficient. Therefore, our experiments show that condensation of gaseous carbon in the interstellar medium leads to the formation of large complex organic molecules the delivery of which to planets could facilitate the formation of biopolymers. However, latter processing of the formed material in different zones could considerably alter the composition of the dust. In the regions with high photon fluxes UV processing of the produced organic leads to the formation of amorphous carbon with a very low level of crystallinity. Latter the level of crystallinity could be increased due to the irradiation of amorphous carbon with high UV doses. This generates curved graphene layers inside amorphous carbon and could finally lead to the formation of fullerene molecules. Alternatively, the level of crystallinity can be increased as a result of the high temperatures, which can be achieved either due to the rearrangement of bonds in a single dust particle or due to coagulation of small nanoparticles. In both cases the amount of released energy should be sufficient to heat the formed nanoparticles to the temperature of a few thousand Kelvins.
Publications
- Growth and Destruction of PAH Molecules in Reactions with Carbon Atoms; Astrophys. J. 836 (1), 32-7 (2017)
S. A. Krasnokutski, F. Huisken, C. Jäger, and Th. Henning
(See online at https://doi.org/10.3847/1538-4357/836/1/32) - Low-temperature Condensation of Carbon; Astrophys. J. 847 (2), 89-7 (2017)
S. A. Krasnokutski, M. Goulart, E. B. Gordon, A. Ritsch, C. Jäger, M. Rastogi, W. Salvenmoser, Th. Henning, and P. Scheier
(See online at https://doi.org/10.3847/1538-4357/aa88a4) - Experimental characterization of the energetics of low-temperature surface reactions; Nat. Astron. 3 , 568-573 (2019)
Th. K. Henning and S. A. Krasnokutski
(See online at https://doi.org/10.1038/s41550-019-0729-8) - Formation of a long-lived cyclic isomer of ethylenedione; Phys. Chem. Chem. Phys. 21 (24), 12986-12990 (2019)
S. A. Krasnokutski, O. Tkachenko, C. Jäger, and Th. Henning
(See online at https://doi.org/10.1039/c9cp01616c) - Fullerene Oligomers and Polymers as Carriers of Unidentified IR Emission Bands; Astrophys. J. 874 (2), 149-6 (2019)
S. A. Krasnokutski, M. Gruenewald, C. Jäger, F. Otto, R. Forker, T. Fritz, and Th Henning
(See online at https://doi.org/10.3847/1538-4357/ab095d)
