Non-thermal ion desorption from nitrilebearing astrophysical ice analogues studied by electron and heavy ion bombardment

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1 Non-thermal ion desorption from nitrilebearing astrophysical ice analogues studied by electron and heavy ion bombardment Fabio Ribeiro, Guilherme C. Almeida, Wania Wolff, Enio Frota da Silveira, Maria Luiza Rocco, Heloisa M. Boechat-Roberty

2 CH 3 CN CH 3 CH CN Several organic and inorganic nitriles and isonitriles CH CHCN Molecules in the Interstellar Medium or Circumstellar Shells (as of 6/16) CHCN

3 Relevant Interstellar Nitriles Increasing complexity of the organic C N series Belloche et al. Science, 14, 345, CH 3 CN CH 3 CH CN CH CHCN CHCN

4 Relevant Interstellar Nitriles Very abundant in space (very common in star forming regions) Important in the formation of amino acids; CH 3 CN is a good probe to estimate temperature and column densities based on observations of a single rotational transition. Tracer for Hot Molecular Cores (HMCs) Enhanced abundance of CH 3 CN in warm (T = 1 3 K) and dense (nh = cm 3 ) environments;

5 Solar System bodies CH CHCN CH 3 CN CH 3 CH CN Image credit: B. Saxton / NRAO / AUI / NSF.

6 Nitrile Chemistry Problems: How such complex nitriles may be formed? Not enough complex species can be produced in the gas phase by known reaction routes; What is the role played by dust grains/ ice mantles? What is the influence of ionizing radiation? Does ion desorption influence gas abundances? Is their chemistry connected? Is the same chemistry happening in other sources?

7 Laboratory work Surface processes are poorly known; Surface Science Techniques under conditions that resemble those found in the ISM; Non-thermal desorption processes: Electron Stimulated Ion Desorption (ESID) electrons in/ ions out Electron Stimulated Ion Desorption (ESID)

8 Laboratory work Surface processes are poorly known; Surface Science Techniques under conditions that resemble those found in the ISM; Non-thermal desorption processes: ion in/ secondary ions out Plasma Desorption Mass Spectrometry (PDMS)

9 Laboratory experiments - ESID Ion desorption increases at 14 ev, which is 3.5 times the ionization threshold for the CH 3 CN N1s core level at 46 ev. Ribeiro et al. Phys.Chem.Chem.Phys., 15, 17, 7473

10 Counts (arb. units) Counts (arb. units) 15 Acrylonitrile CH CHCN (53 u) H + CH + CH + CH CH CHCN + CH CHCNH H + CH + 3 Isobutyronitrile CHCN (69 u) C H 3 N + CH 3 N + C 3 H + 5 C H CHCNH N ++ C + C H + 3 C H H + CH + N + C 3 H CHC + CHN + H

11 Counts (arb. units) Laboratory experiments - ESID Counts (arb. units) Desorption of ion clusters by electron impact (.3 kev) ( CHCN)C + Isobutyronitrile CHCN (69 u) 15 ( CHCN)C H + m (m=-3) ( CHCN H ( CHCN) CH + ( CHCN) CHC + CH 3 (CH CN (CH CHCN) C + (CH CHCN) C H + m (m=-3) (CH CHCN) C 3 H + m (m=-3) (CH CHCN) H (CH CHCN) C H m N + (m=-3) Ribeiro et al. Phys.Chem.Chem.Phys., 15, 17, 7473

12 Counts (Arb. units) Laboratory experiments - PDMS Counts (Arb. units) Isobutyronitrile CHCN (69 u) 1 1 CHCNH + ( CHCN H + n (n=1-) 1 5 H + H 3 + CH + N + CH + 3 C H + 3 CH N + C 3 H + C 3 + CH + C 3 H + 3 CH 3 CHCN + CHC + CHCNH ( CHCN)H O + ( CHCN) CHC Desorption of CHCN ion clusters PDMS mass spectrum of CHCN at 1 K

13 Laboratory experiments - PDMS Counts (Arb. units) 6 Acetonitrile CH 3 CN (41u) 5 CN)CH + 3 CN H + CH 3 CNH H + 5 H + C + CH CH C H + 3 CH 3 N + CH 3 CN + CHCN + H PDMS mass spectrum of CH 3 CN at 1 K. Inset: Desorption of CH 3 CN ion clusters

14 ESID and PDMS comparison 1 - ESID PDMS Stronger fragmentation in ESID Proton transfer processes during ion desorption

15 ESID and PDMS comparison 1 - ESID PDMS Stronger fragmentation on surface in ESID in respect to CH 3 CN; Similar Ion Yield for CHCN + ( = 69) ion desorption in ESID and PDMS; Proton transfer processes during ion desorption.

16 Summary Remarks Strong fragmentation on surface and ion desorption is oberseved for all studied nitriles; Fragmentation caused by electrons is initiated by Coulomb explosion after Auger electronic decay; Predominance for saturated and protonated fragments desorption. The last might play a role in ion-neutral reactions on gas-phase; Cluster ion desorption may be a route for delivering for complex molecules (nitriles) to the cold interstellar and circumstellar material exposed to ionizing radiation Similar conclusions can be ascribed to the Titan atmosphere, where a set of complex nitriles is known to exist

17 Acknowledgements Thank you for your attention!