The deuterated isotopologues of NH3

Transcription

1 The deuterated isotopologues of NH3 F. Daniel1 A. Faure1, C. Rist1, M. Gérin2, E. Roueff2, D. Lis2, L. Wiesenfeld1, P. Hily-Blant1 1 IPAG, Grenoble 2 LERMA, Paris

2 Isotopic ratios to trace our origins - Earth formation : volatile elements (e.g. N2, H2O) have been delivered lately through comet and asteroid bombardement

3 Isotopic ratios to trace our origins - Earth formation : volatile elements (e.g. N2, H2O) have been delivered lately through comet and asteroid bombardement isotopes (D, 15N) put constraints on the models of formation [1] [1] Ceccarelli et al., 2014, prpl, 914, 859

4 Isotopic ratios to trace our origins - Earth formation : volatile elements (e.g. N2, H2O) have been delivered lately through comet and asteroid bombardement isotopes (D, 15N) put constraints on the models of formation [1] source : ESA [1] Ceccarelli et al., 2014, prpl, 914, 859

5 Isotopic ratios to trace our origins - Earth formation : volatile elements (e.g. N2, H2O) have been delivered lately through comet and asteroid bombardement isotopes (D, 15N) put constraints on the models of formation [1] factor 10 characteristic of the cosmic D/H abundance source : ESA [1] Ceccarelli et al., 2014, prpl, 914, 859

6 Isotopic ratios to trace our origins - Earth formation : volatile elements (e.g. N2, H2O) have been delivered lately through comet and asteroid bombardement isotopes (D, 15N) put constraints on the models of formation [1] factor 2 factor 10 low proportion of volatiles would come from comets characteristic of the cosmic D/H abundance source : ESA [1] Ceccarelli et al., 2014, prpl, 914, 859

7 The deuterated isotopologues of NH3 - fundamental isotopic ratio : [D]/[H] ~ [1] - process of chemical enrichement the abundance of deuterated isotopologues is largely higher than expected from statistical considerations [2] : [NH2D] / [NH3] ~ [ND2H] / [NH2D] ~ [ND3] / [ND2H] ~ 0.03 [ND3] / [NH3] ~ [1] Linsky et al., 2006, ApJ, 647, 1106 [2] Roueff et al., 2005, A&A, 438, 585

8 The deuteration of NH3 formation of NH3 He+ 4H2 e- N2 N+ NH4+ NH3 (1) (gas phase) - the reaction N+ + H2 NH+ + H requires an energy ~170K - the internal energy of ortho-h2 accelerates the sequence if o-h2 / p-h2 > 10-4

9 The deuteration of NH3 formation of NH3 He+ 4H2 e- N2 N+ NH4+ NH3 (1) (gas phase) - the reaction N+ + H2 NH+ + H requires an energy ~170K - the internal energy of ortho-h2 accelerates the sequence if o-h2 / p-h2 > 10-4 deuteration of NH3 solid phase: probabilistic approach where the abundances of multi-deuterated species are D/H gas phase: complex reactivity network with a competition between formation and destruction processes Schematically: 1/ formation of NH3 through (1) 2/ proton transfer with XH+ et XD+ ions NHnD4-n+ n [1;4] 3/ followed by dissociative recombination with e- NHnD3-n n [1;3]

10 The deuteration of NH3 formation of NH3 He+ 4H2 e- N2 N+ NH4+ NH3 (1) (gas phase) - the reaction N+ + H2 NH+ + H requires an energy ~170K + -4 T : deuteration ofthe H3sequence becomesifinefficient - the internal energy of high ortho-h accelerates o-h / p-h > high level of deuteration observed in Orion BN KL? deuteration of NH3 solid phase: probabilistic approach where the abundances of multi-deuterated species are D/H gas phase: complex reactivity network with a competition between formation and destruction processes Schematically: 1/ formation of NH3 through (1) 2/ proton transfer with XH+ et XD+ ions NHnD4-n+ n [1;4] 3/ followed by dissociative recombination with e- NHnD3-n n [1;3]

11 The deuteration of NH3 formation of NH3 He+ 4H2 e- N2 N+ NH4+ NH3 (1) (gas phase) - the reaction N+ + H2 NH+ + H requires an energy ~170K - the internal energy of ortho-h2 accelerates the sequence if o-h2 / p-h2 > 10-4 deuteration of NH3 solid phase: probabilistic approach where the abundances of multi-deuterated species are D/H gas phase: complex reactivity network with a competition between formation and destruction processes Schematically: lowthrough T : desorbtion 1/ formation of NH (1) of the molecules formed on grains? 3 NHnD4-n+ n [1;4] 2/ proton transfer with XH+ et XD+ ions 3/ followed by dissociative recombination with e- NHnD3-n n [1;3]

12 The deuteration of NH3 Model predictions [1] : solid phase: the abundance ratio is ~ constant, independently of the physical conditions gas phase: to first order, the gas phase chemistry would give ratios : [1] Rodgers & Charnley, 2001, ApJ, 553, 613

13 The deuteration of NH3 Model predictions [1] : solid phase: the abundance ratio is ~ constant, independently of the physical conditions 1.5 would give ratios 1.7: gas phase: to first order, the gas phase chemistry ''Ideally'', a precise determination of the ND2H / NH2D and ND3 / ND2H abundance ratio should allow to discriminate between the two formations paths [1] Rodgers & Charnley, 2001, ApJ, 553, 613

14 The deuteration of NH3 Model predictions [1] : solid phase: the abundance ratio is ~ constant, independently of the physical conditions 1.5 would give ratios 1.7: gas phase: to first order, the gas phase chemistry ''Ideally'', a precise determination of the ND2H / NH2D and ND3 / ND2H abundance ratio should allow to discriminate between the two formations paths typically, an accuracy better than a factor ~2 is needed on the estimate of the abundance ratio [1] Rodgers & Charnley, 2001, ApJ, 553, 613

15 Accuracy : Radiative Transfer Emission observed energy levels : out of thermodynamical equilibrium (LTE) - collisions / molecules in the gaz (H2, He,...) Cij = n(h2) Rij - radiation (molecule(s), continuum,...) I

16 Accuracy : Radiative Transfer Study on the 14N/15N abundance ratio in the star forming region B1b (perseus) [1] B1c B1b B1b SCUBA (850 μm) [1] Daniel et al., 2013, A&A, 560, 3

17 Accuracy : Radiative Transfer Study on the 14N/15N abundance ratio in the star forming region B1b (perseus) [1] B1c B1b B1b Gerin Gerinetetal. al.(2009) (2009)[2]: [2]: analysis analysisbased basedon onlte LTE approximation approximation 15 NH D/ SCUBA (850 μm) 2DD==470 NH2 D/15NH NH [2] Gérin et al., 2009, A&A, 498, 9 [1] Daniel et al., 2013, A&A, 560, 3

18 Accuracy : Radiative Transfer Study on the 14N/15N abundance ratio in the star forming region B1b (perseus) [1] B1c B1b B1b Gerin Gerinetetal. al.(2009) (2009)[2]: [2]: analysis analysisbased basedon onlte LTE approximation approximation 15 NH D/ SCUBA (850 μm) 2DD==470 NH2 D/15NH NH Daniel Danieletetal. al.(2013) (2013)[1]: [1]: analysis analysisbased basedon onrt RT modeling modeling 15 NH D/ = NH2D/15NH NH2D 2D = 230 [2] Gérin et al., 2009, A&A, 498, 9 [1] Daniel et al., 2013, A&A, 560, 3

19 Accuracy : Radiative Transfer Study on the 14N/15N abundance ratio in the star forming region B1b (perseus) [1] B1c B1b B1b Gerin Gerinetetal. al.(2009) (2009)[2]: [2]: analysis analysisbased basedon onlte LTE approximation approximation 15 NH D/ SCUBA (850 μm) 2DD==470 NH2 D/15NH NH Daniel Danieletetal. al.(2013) (2013)[1]: [1]: analysis analysisbased basedon onrt RT modeling modeling Daniel Danieletetal. al.(2016) (2016)[3]: [3]: analysis analysisbased basedon onrt RT modeling modeling++new newrates rates 15 NH D/ = NH2D/15NH NH2D NH D/ ==280 2D = 230 NH2 2D/15NH NH2D D [3] Daniel et al., 2016, arxiv: [2] Gérin et al., 2009, A&A, 498, 9 [1] Daniel et al., 2013, A&A, 560, 3

20 Accuracy : Radiative Transfer Study on the 14N/15N abundance ratio in the star forming region B1b (perseus) [1] Apart for N15NH+, ratios cluster around 300 : against fractionation effects not clear with the initial 14N/15N NH2D estimate B1c B1b B1b Gerin Gerinetetal. al.(2009) (2009)[2]: [2]: analysis analysisbased basedon onlte LTE approximation approximation 15 NH D/ SCUBA (850 μm) 2DD==470 NH2 D/15NH NH Daniel Danieletetal. al.(2013) (2013)[1]: [1]: analysis analysisbased basedon onrt RT modeling modeling Daniel Danieletetal. al.(2016) (2016)[3]: [3]: analysis analysisbased basedon onrt RT modeling modeling++new newrates rates 15 NH D/ = NH2D/15NH NH2D NH D/ ==280 2D = 230 NH2 2D/15NH NH2D D [3] Daniel et al., 2016, arxiv: [2] Gérin et al., 2009, A&A, 498, 9 [1] Daniel et al., 2013, A&A, 560, 3

21 Accuracy : Radiative Transfer Study on the 14N/15N abundance ratio in the star forming region B1b (perseus) [1] Apart for N15NH+, ratios cluster around 300 : against fractionation effects not clear with the initial 14N/15N NH2D estimate B1c B1b B1b Gerin Gerinetetal. al.(2009) (2009)[2]: [2]: analysis analysisbased basedon onlte LTE approximation approximation Daniel Danieletetal. al.(2013) (2013)[1]: [1]: Daniel et al. (2016) [3]: Daniel et al. (2016) [3]: analysis analysisbased basedon onrt RT analysis based on RT 15 analysis based on RT modeling NH D/ NH D = SCUBA (850 μm) modeling 2 2 NH D/ NH D = 470 modeling Two ingredients 2'insure' the accuracy : 2 modeling++new newrates rates 15 - the method of analysis NH D/ 15 NH 2 2DD==230 NH D/ NH 230 NH D/1515NH D = the accuracy of collisional rate coefficients NH2 2D/ NH2 2D = 280 [3] Daniel et al., 2016, arxiv: [2] Gérin et al., 2009, A&A, 498, 9 [1] Daniel et al., 2013, A&A, 560, 3

22 Rate coefficients for the NH3 isotopologues collisions with He - NH3 - NH3 - NH2D : Green et al [1] - ND2H - NH3 ; ND3 : Machin et al [4] : Machin et al [2] : Machin et al [3] : Yang et al [5] collisions with H2 - NH3 - NH3 - NH3 - ND2H [1] [2] [3] [4] [5] : Danby et al. 1987, 1988 [6,7] : Offer et al [8] : Maret et al [9] : Wiesenfeld et al [10] Green et al., 1976, JCP, 64, 3463 Machin et al., 2005, JPhB, 38, 1519 Machin et al., 2006, A&A, 460, 953 Machin et al., 2007, A&A, 465, 647 Yang et al., 2008, EPJD, 47, 351 [6] Danby et al., 1987, JPhB, 20, 1039 [7] Danby et al., 1988, MNRAS, 235, 229 [8] Offer et al., 1989, JPhB, 22, 439 [9] Maret et al., 2009, A&A, 399, 425 [10] Wiesenfeld et al., 2011, MNRAS, 413, 509

23 Rate coefficients for the NH3 isotopologues - Schrodinger equation - Born-Oppenheimer decoupling of the electronic and nuclear motions 1/ electronic / nuclear interactions : Potential Energy Surface (PES) 2/ nuclear motion on this PES

24 Rate coefficients for the NH3 isotopologues - Schrodinger equation - Born-Oppenheimer decoupling of the electronic and nuclear motions 1/ electronic / nuclear interactions : Potential Energy Surface (PES) 2/ nuclear motion on this PES The NH3 - H2 [1] PES is modified to treat the NHnD3-n - H2 system [2,3]: 1/ modification of the center of mass 2/ rotation of the coordinate system 3/ fit of the ab-initio PES points [1] Maret et al., 2009, MNRAS, 399, 425 [2] Machin et al., 2006, MNRAS, 460, 953 [3] Wiesenfeld et al., 2011, MNRAS, 413, 509

25 Rate coefficients for the NH3 isotopologues - Schrodinger equation - Born-Oppenheimer decoupling of the electronic and nuclear motions 1/ electronic / nuclear interactions : Potential Energy Surface (PES) 2/ nuclear motion on this PES The NH3 - H2 [1] PES is modified to treat the NHnD3-n - H2 system [2,3]: 1/ modification of the center of mass 2/ rotation of the coordinate system 3/ fit of the ab-initio PES points Collisional dynamics solved with the codes MOLSCAT and Hibridon [1] Maret et al., 2009, MNRAS, 399, 425 [2] Machin et al., 2006, MNRAS, 460, 953 [3] Wiesenfeld et al., 2011, MNRAS, 413, 509

26 Rate coefficients for the NH3 isotopologues - Schrodinger equation - Born-Oppenheimer decoupling of the electronic and nuclear motions 1/ electronic / nuclear interactions : Potential Energy Surface (PES) 2/ nuclear motion on this PES The NH3 - H2 [1] PES is modified to treat the NHnD3-n - H2 system [2,3]: 1/ modification of the center of mass 2/ rotation of the coordinate system 3/ fit of the ab-initio PES points Collisional dynamics solved with the codes MOLSCAT and Hibridon cross section [1] Maret et al., 2009, MNRAS, 399, 425 [2] Machin et al., 2006, MNRAS, 460, 953 [3] Wiesenfeld et al., 2011, MNRAS, 413, 509

27 Rate coefficients for the NH3 isotopologues - Schrodinger equation - Born-Oppenheimer decoupling of the electronic and nuclear motions 1/ electronic / nuclear interactions : Potential Energy Surface (PES) 2/ nuclear motion on this PES The NH3 - H2 [1] PES is modified to treat the NHnD3-n - H2 system [2,3]: 1/ modification of the center of mass 2/ rotation of the coordinate system 3/ fit of the ab-initio PES points Collisional dynamics solved with the codes MOLSCAT and Hibridon rate coefficient [1] Maret et al., 2009, MNRAS, 399, 425 [2] Machin et al., 2006, MNRAS, 460, 953 [3] Wiesenfeld et al., 2011, MNRAS, 413, 509

28 rate coefficients for NH2D / H2 : levels up to JKa,Kc = 770 (E ~ 735 K) and temperatures in the range T = 5-300K

29 rate coefficients for NH2D / H2 : levels up to JKa,Kc = 770 (E ~ 735 K) and temperatures in the range T = 5-300K Comparison with the rates previsously calculated with He [1] [1] Machin et al., 2006, A&A, 460, 953

30 rate coefficients for ND2H and ND3 with H2 : levels up to ~ 100 cm-1 and temperatures in the range T = 5-50K Comparison with the rates previsously calculated with H2 [1] [1] Wiesenfeld et al., 2011, MNRAS, 413, 509

31 Experimental validation of the PES differential cross section : ND3 H2 [1] [1] Tkac et al., 2015, Mol. Ph., 113, 3925

32 Experimental validation of the PES differential cross section : ND3 H2 [1] Ma et al [2] theoretical characterization of the resonnance features for NH3- H2 and ND3 - H2 future crossed beam experiment to test the validity of the PES: position and strength of the resonnances visible with a resolution of 2 cm-1 [1] Tkac et al., 2015, Mol. Ph., 113, 3925 [2] Ma et al., 2015, JCP, 143, 4312

33 Observations of the NH3 isotopologues Roueff et al., 2005, A&A, 438, 585

34 Observations of the NH3 isotopologues Roueff et al., 2005, A&A, 438, 585 o nly 2 o bje cts whe re the 3 de u te rate d NH 3 isotop o lo gu e s we re dete cte d

35 Observations of the NH3 isotopologues Roueff et al., 2005, A&A, 438, 585 physical models of the sources has been recently updated : - Barnard 1 : Daniel et al [1] E : Bacmann et al [2] (in L1689N) [1] Daniel et al., 2013, A&A, 560, 3 [2] Bacmann et al., 2016, arxiv:

36 Impact of the new NH2D / H2 rate coefficients re-evaluation of the NH2D abundance in B1b old [NH2D] new [NH2D]

37 Impact of the new NH2D / H2 rate coefficients re-evaluation of the NH2D abundance in B1b - abundance profile largely affected by the rate coefficients - column density unchanged ( cm cm-2) - the 14N/15N ratio sligthly modified ( )

38 Impact of the new ND2H and ND3 rates p-nd2h o-nd2h o-nh2d m-nd E

39 Observations of the NH3 isotopologues from Daniel et al., 2016, arxiv: old values refere to Roueff et al., 2005, A&A, 438, 585 New estimates of the abundance ratios within a factor 1-4 with the initial estimates

40 Grain vs. gas phase?

41 Grain vs. gas phase? - ND2H / NH2D and ND3 / ND2H would favor a solid phase formation

42 Grain vs. gas phase? - ND2H / NH2D and ND3 / ND2H would favor a solid phase formation - ratios between spin isomers also provide constraints

43 Grain vs. gas phase? - ND2H / NH2D and ND3 / ND2H would favor a solid phase formation - ratios between spin isomers also provide constraints grain formation: proportional to nuclear spin statistical weights

44 Grain vs. gas phase? - ND2H / NH2D and ND3 / ND2H would favor a solid phase formation - ratios between spin isomers also provide constraints grain formation: proportional to nuclear spin statistical weights gas phase formation: complex trend that depends on physical conditions n(h2) = 105 cm-3 T = 12K from Harju et al., 2016, in prep.

45 Grain vs. gas phase? - ND2H / NH2D and ND3 / ND2H would favor a solid phase formation - ratios between spin isomers also provide constraints grain formation: proportional to nuclear spin statistical weights gas phase formation: complex trend that depends on physical conditions n(h2) = 105 cm-3 T = 12K spin statistical weigths from Harju et al., 2016, in prep.

46 Grain vs. gas phase? - ND2H / NH2D and ND3 / ND2H would favor a solid phase formation - ratios between spin isomers also provide constraints grain formation: proportional to nuclear spin statistical weights gas phase formation: complex trend that depends on physical conditions 5 B1b -3 n(h2) = 10 cm T = 12K 16293E o/p NH2D o/p ND2H 2* 2** * Lis et al 2006 [1] ** Gérin et al 2006 [2] from Harju et al., 2016, in prep. [1] Lis et al., 2006, ApJ, 636, 916 [2] Gérin et al., 2006, A&A, 454, L63

47 Conclusions - new rate coefficients for NH2D, ND2H and ND3 with H2 large variations with the rates previously reported

48 Conclusions - new rate coefficients for NH2D, ND2H and ND3 with H2 large variations with the rates previously reported - influence on astrophysical models (the B1b and 16293E cases) : - re-evaluation of the abundance ratios ND2H / NH2D and ND3 / ND2H - determination of the spin isomer ratios : ortho/para NH2D and ortho/para ND2H

49 Conclusions - new rate coefficients for NH2D, ND2H and ND3 with H2 large variations with the rates previously reported - influence on astrophysical models (the B1b and 16293E cases) : - re-evaluation of the abundance ratios ND2H / NH2D and ND3 / ND2H - determination of the spin isomer ratios : ortho/para NH2D and ortho/para ND2H both would favor the solid phase chemistry

50 Conclusions - new rate coefficients for NH2D, ND2H and ND3 with H2 large variations with the rates previously reported - influence on astrophysical models (the B1b and 16293E cases) : - re-evaluation of the abundance ratios ND2H / NH2D and ND3 / ND2H - determination of the spin isomer ratios : ortho/para NH2D and ortho/para ND2H both would favor the solid phase chemistry drawbacks : - source sample (only 2 objects with complex structures) - reliability of the gas phase chemistry predictions?

51 Conclusions - new rate coefficients for NH2D, ND2H and ND3 with H2 large variations with the rates previously reported - influence on astrophysical models (the B1b and 16293E cases) : - re-evaluation of the abundance ratios ND2H / NH2D and ND3 / ND2H - determination of the spin isomer ratios : ortho/para NH2D and ortho/para ND2H both would favor the solid phase chemistry drawbacks : - source sample (only 2 objects with complex structures) - reliability of the gas phase chemistry predictions? perspectives : - current observational facilities (ALMA) easy to enlarge the sample - deuteration in protostellar disks? - comparison with NH3 deuteration fraction in comets? material reprocessed by comparison to the D/H inherited from the PSN stage?