REACTIONS OF ENERGETIC CARBON AND NITROGEN IN H2O, NH3 AND CH4 ICES AND IMPLICATIONS IN COSMIC CHEMISTRY

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REACTIONS OF ENERGETIC CARBON AND NITROGEN IN H2O, NH3 AND CH4 ICES AND

IMPLICATIONS IN COSMIC CHEMISTRY

K. Rössler, B. Nebeling

To cite this version:

K. Rössler, B. Nebeling. REACTIONS OF ENERGETIC CARBON AND NITROGEN IN H2O, NH3

AND CH4 ICES AND IMPLICATIONS IN COSMIC CHEMISTRY. Journal de Physique Colloques,

1987, 48 (C1), pp.C1-691-C1-692. �10.1051/jphyscol:19871111�. �jpa-00226253�

JOURNAL DE PHYSIQUE

Colloque C1, supplkment au no 3, Tome 48, mars 1987

REACTIONS OF ENERGETIC CARBON AND NITROGEN IN H20, NH3 AND CH4 ICES AND IMPLICATIONS IN COSMIC CHEMISTRY

K. ROSSLER and B. NEBELING

Institut fur Chemie 1 (Nuklearchemie), der Kernforschungsanlage Julich, 0-5170 Julich, F.R.G.

Abstract : Atcans or ions with kinetic energies exceeding a few eV are able to undergo unconventional chemical reactions such as endothermic processes and those with high energy of activation, amng them atormolecule reactions. This ~crcalled hot atom chemistry (1) is of importance for the interactions of accelerated particles frcan solar wind, solar flares, cosmic rays, radiation belts of planets and their satellites, colliding interstellar gas and dust clouds, shock waves, etc...

with solids in space, particularly with the icy matter of interplanetary and interstellar dust, comets, meteorite parent bodies, surfaces of icy planets or satellites and planetary rings (2-4). More important than the chemical reactions of the primary projectiles seem to be those of the energetic secondaries, created by knock-on of target at- (5). These processes may add effectively to the classical thermal or epithermal ion molecule and plasma chemical reactions and the radiolytical., photolytid, and other radial processes studied in cosmic chemistry hitherto.

Laboratory simulation is performed by recoil processes after nuclear reactions induced by protons or deuterons from a cyclotron. Hot carbon and nitrogen atoms with kinetic energies of 2 to 3 MeV are created by the 14~(p,o()1k, 160(p,dpn)1k, 160(pp(

) l%J, and 12c(d,n)13~ nuclear reactions in H20-ice, frozen NH3 and CHq at 77 K. The newly formed chemical products are detected via the radioactivity of their 1 k and

labels by radio-gas- and -high performance liquid chromatography.

Table 1 : Products formed by l k and l% hot atoms in some frozen systems at 77K.

System major products minor products

CH3m2! F 4 r

f ormamidine

guanidine, cyanamide

m,

*

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19871111

Cl-692 JOURNAL DE PHYSIQUE

Table 1 shows some of the products of hot reactions, which have to be studied at a low radiation dose level (4 0.1 eV per target molecule) in order to avoid radiolytical changes of the primary species.

The mechanisms of formation are 1) abstraction of hydrogen atoms, 2) insertion into C-HI N-H or 0-H bonds, 3) head-on collision with one target molecule which can lead to addition or the ejection of hydrogen atoms, 4) fast successive collisions with two or more target mlecules (collision ccanplex), accmpanied by hydrogen ejection.

Substitution reactions seem to be less probable for the light target molecules studied. However, spontaneous recombination of defects in the collision cascade can play a certain role as a physical reaction mechanism besides the more chemical ones cited above. Fragmentation of excited intermediates is less frequent than in gas phase systems, since the energy can easily be transferred to neighbours.

The hot processes can contribute effectively to the build-up of organics and biamlecule precursors in icy matter, since a great variety of basic products is formed by one or only few fast successive reaction steps. Carbon atoms seem to lead to more sophisticated products than nitrogen. For targets with higher complexity than the ones studied in this work, even m r e interesting products can be expected.

The abundance of primary and secondary accelerated atoms and ions underlines the importance of this type of reactions for chemical evolution in space.

References

(1) Stijcklin G., Chemie HeiBer Atome, Verlag Chemie, Weinheim 1969 ; Chimie des atomes chauds, Masson et Cie, Paris 1972.

(2) Rijssler K., Proc. 3rd Int. Conf. Radiation Effects in Insulators, Guildford (UK), 15-19 July 1985, in press.

(3) &sler K., ESA-SP 241 (1985), 175-88.

(4) Rijssler K., Jung H.J. and Nebeling B., Adv. Space Reas.

4

(5) Rijssler K. and Eich G., in "Properties and Interactions of Interplanetary Dust", R.H. Giese, P. Lamy (Eds.), Reidel, Dordrecht (1985), 351-356.