Laboratory evidence for isotope effects of surface processes. Emanuele Congiu François Dulieu, Henda Chaabouni LERMA Laboratory

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1 Laboratory evidence for isotope effects of surface processes Emanuele Congiu François Dulieu, Henda Chaabouni LERMA Laboratory

2 COST Action Our Astrochemical History

3 Desorption (3) Accretion (1) COST Action Our Astrochemical History

4 The FORMOLISM set-up H D

5 Sticking efficiency: H2 vs D2 Sticking Flux in = Flux out Matar et al 2010; Chaabouni et al 2012

6 Sticking efficiency: H2 vs D2 D2 H2 Different sticking coefficients for H2 and D2 Matar et al 2010; Chaabouni et al 2012

7 Sticking efficiency: H2 vs D2 If we suppose that differences between H2 and D2 are due to their mass, then their sticking efficiency should be the same if the temperature is rescaled by a factor of 2...

8 Sticking efficiency: H vs D Our model is able to fit the theoretical values for H and D by Buch et al 1991 Matar et al 2010; Chaabouni et al 2012

9 Surface reaction: HNCO + H/D Hydrogenation of isocyanid acid... Will it lead to formamide? HNCO + 2H NH2CHO? Noble et al. 2015, A&A, 576, A91

10 Surface reaction: HNCO + H/D a) HNCO (m/z=43) b) HNCO + H (m/z=43) a b Noble et al. 2015, A&A, 576, A91 COST Action Our Astrochemical History

11 Surface reaction: HNCO + H/D a) HNCO (m/z=43) c) HNCO + D (m/z=43) d) HNCO + D (m/z=44) DNCO a c d Noble et al. 2015, A&A, 576, A91 COST Action Our Astrochemical History

12 Surface reaction: HNCO + H/D a) HNCO (m/z=43) c) HNCO + D (m/z=43) d) HNCO + D (m/z=44) DNCO No signal at m/z=47 a (NHDCDO) Noble et al. 2015, A&A, 576, A91 COST Action Our Astrochemical History

13 Surface reaction: HNCO + H/D Proposed reaction scheme: The expected hydrogenation of HNCO to NH2CHO does not readily occur and thus has a very high barrier Noble et al. 2015, A&A, 576, A91 COST Action Our Astrochemical History

14 H/D scrambling in ice mantles Deposition of binary layered ices at 10 K Detection of the desorbed species via QMS and temperature-programmed desorption (TPD) See also Ratajczak et al 2009; Ratajczak et al 2011

15 H/D scrambling in ice mantles Very efficient H/D exchange on the onset of desorption gas phase =/= solid phase!

16 H/D scrambling in ice mantles Number of D is conserved! Main reaction at play:

17 H/D (or OH/OD) scrambling in ice mantles We also carried out an experiment to determine if an H/D scrambling was going on or if it was the whole hydroxyl group involved in the exchange instead...?

18 H/D (or OH/OD) scrambling in ice mantles We also carried an experiment to determine if an H/D scrambling was going on or if it was the whole idroxyl group involved in the exchange instead...

19 Desorption: isotopologues of hydrogen Desorption of pure H2, HD, D2 Dulieu et al 2005 Amiaud et al in prep.

20 Desorption: isotopologues of hydrogen Desorption of mixtures of isotopologues Dulieu et al 2005 Amiaud et al in prep.

21 Desorption: isotopologues of hydrogen Desorption of mixtures of isotopologues - isotope segregation Dulieu et al 2005 Amiaud et al in prep.

22 Desorption: isotopologues of hydrogen Desorption of mixtures of isotopologues - isotope segregation Eads=60meV, t(resid)>10^13 days Eads=30meV, t(resid)>0.01 days!!! Eads,H2 Dulieu et al 2005 Amiaud et al in prep. D2 kicks out HD and H2 molecules HD and H2 are pushed toward shallower binding sites

23 Case of water (Speedy et al 1996) D atoms and D-bearing molecules are better retained on interstellar dust grains

24 Suggestions for future research (laboratory) -investigation of desorption properties of ice mixtures of water isotopologues the fact that deuterated species are pretty systematically less volatile could explain overabundant D2O/HDO ratios in select interstellar regions (Talk by Audrey Coutens) Implications for the origin of water on Earth, comets or asteroids? What really governs the HDO/H2O ratio in cometary ices?

25 Suggestions for future research (laboratory) Cometary ices might have a story to tell...