IR Spectroscopy and physicochemical effects on astrophysical ices produced by energetic ions collisions

Transcription

1 IR Spectroscopy and physicochemical effects on astrophysical ices produced by energetic ions collisions Ana Lucia de Barros Physics Department Centro Federal de Educação Tecnológica Celso Suckow da Fonseca Rio de Janeiro, Brazil Guilherme C. Almeida Physics Department Pontifícia Universidade Católica Rio de Janeiro, Brazil Cíntia A. P. da Costa Physics Department Pontifícia Universidade Católica Rio de Janeiro, Brazil Enio F. da Silveria Physics Department Pontifícia Universidade Católica Rio de Janeiro, Brazil INTERNATIONAL SYMPOSIUM AND WORKSHOP ON ASTROCHEMISTRY ISWA Campinas July 2016

2 Astrophysical ices Orion Nebula The grains are covered with an icy mantle formed from simple molecules (H 2 O, CO, CO 2, O, CH 4, etc). Energetic processes induced by: - photons, - electrons (high and low-energy), - ions (cosmic rays, solar wind). Carina Nebula NASA website NASA website Irradiation induces chemical modification and desorption of species from the ice.

3 Astrophysical ices: energetic processes state of the art Projectiles: photons (e.g. new molecules, destruction/formation cross sections, photodesorption ) H 2 O:CH 3 OH:NH 3 :CO:CO 2 Muñoz Caro et al., Nature 416 (2002) 403 electrons (low and high energy range) (e.g. same as Photons) ~1-20 ev CH 3 COOH:NH 3 Lafosse et al., PCCP 8 (2006) 5564 ions (mainly H, He, C, O ions in ~50 kev and ~2 MeV energy range) (e.g. new molecules, destruction/formation cross sections, sputtering) In this work H + and He + at 1.5 MeV H 2 O Strazzulla & Baratta, Europhysics Letter 18 (1992) 517

4 PUC Van de Graaff Accelerator Rio de Janeiro, Brazil INTERNATIONAL SYMPOSIUM AND WORKSHOP ON ASTROCHEMISTRY ISWA Campinas July 2016

5 PUC Van de Graaff Accelerator FTIR Beamline UHV Chamber Overview

6 Experimental details Substrate Kbr window Temperature T = 10 K FTIR spectrometer cryostat irradiation/analysis chamber connection to beam line Pressure in irradiation chamber ~ 2 x 10-8 mbar (~10 K) Samples (ices- O) - in situ gas deposition - thickness ~ mm ( molecules/cm 2 ) - ion penetration depth > ice thickness Ion beam MeV H + and He + - flux ~10 9 ion/cm 2 s - fluence up to 2.0 x ions/cm 2 INTERNATIONAL SYMPOSIUM AND WORKSHOP ON ASTROCHEMISTRY ISWA Campinas July 2016

7 Irradiation Process SALT WINDOWS INFRARED DETECTOR O ICE INFRARED SOURCE GAS INLET CRYOSTAT H + or He + BEAM VACUUM PUMP

8 Absorbance Absrobance(peak area) FTIR spectrum of O ice H + N O 2 He + Non irradiated c = 1.07x10-11 cm 2 d = 2.05x10-12 cm N(0) =ln10. Sp /A p = 2.26 x1018 v Fluence 2500 ( ions cm -2 ) Wavenumbers (cm -1 ) Absorbance d N ln(10) A( cm / molecule ) Abs( ) total band absorbance A integrated absorbance

9 Absorbance Observed Daughter Species O 0.8 O O 3 O O O O N O 5 3 O Wavenumbers (cm -1 ) INTERNATIONAL SYMPOSIUM AND WORKSHOP ON ASTROCHEMISTRY ISWA Campinas July 2016

10 Column density (10 16 molecules cm -2 ) Daughter Species 1.5 MeV H + O H + NO 2 NO O 3 1 O 2 O 3 O O Fluence (10 11 ions cm -2 )

11 Column density (10 16 molecules/cm 2 ) Daughter Species 1.5 MeV He + O 1 He + NO 2 NO O 3 O O 3 O O 5 1E Fluence (10 11 ions cm -2 )

12 Column density (10 17 molecules/cm 2 ) Precursors Integrated (Destruction + Formation) Cross Sections Destruction d O Fluence (10 15 impacts/cm 2 )

13 Column density (10 16 molecules/cm 2 ) Column density (10 17 molecules/cm 2 ) Precursors Integrated (Destruction + Formation) Cross Sections Destruction d O Fluence (10 15 impacts/cm 2 ) N x O y f Formation Fluence (10 15 impacts/cm 2 ) N x O y (Formation + Destruction) Cross Sections

14 Column density (10 16 molecules/cm 2 ) Column density (10 17 molecules/cm 2 ) Precursors Integrated (Destruction + Formation) Cross Sections Destruction d O 3,0 2,5 Destruction Fluence (10 15 impacts/cm 2 ) 2,0 1,5 N x O y 1,0 0,5 f Formation 0, Fluence (10 15 impacts/cm 2 ) N x O y (Formation + Destruction) Cross Sections

15 Column density (10 16 molecules/cm 2 ) Column density (10 17 molecules/cm 2 ) CH Precursors 3 OH Integrated (Destruction + + Formation) Cross Cross Sections 4 3,5 3 Destruction d 2,5 2 Formation f 1,5 O 3,0 2,5 Destruction Fluence (10 15 impacts/cm 2 ) 2,0 1,5 N x O y 1,0 0,5 f Formation 0, Fluence (10 15 impacts/cm 2 )

16 Column density (10 16 molecules/cm 2 ) Column density (10 17 molecules/cm 2 ) Precursors Integrated (Destruction + Formation) Cross Sections 4 3,5 3 2,5 2 Destruction d Formation f regeneration of O from its daughter molecules 1,5 O 3,0 2,5 Destruction Fluence (10 15 impacts/cm 2 ) 2,0 1,5 N x O y 1,0 0,5 f Formation 0, Fluence (10 15 impacts/cm 2 )

17 Average (integrated) Cross Sections E in = 1.5 MeV H + 0 dn df i j i f, ijn j Li d, i N i Y i H 2 O O 100Å N i is the column density of molecular species i; f and d formation and destruction cross sections; L i and Y i are their layering and sputtering yields; Approximate Equations... Precursor molecule Daughter molecule dn df dnk f, k1n1 d, k N df k 1 f,1k Nk d,1n1 k There is no chemical reaction between daughter species!!!!!

18 Cross Sections Destruction and formation cross-sections (10-14 cm 2 ) of O with H + Molecules 10 K at 1.5 MeV Formation cross-section Destruction crosssection Precursor O - (2.1 ± 0.5) NO 2 (1.1 ± 0.2) (1.3 ± 0.2) O 2 (0.09 ± 0.01) (3.1 ± 0.6) Daughters NO (0.54 ± 0.08) (1.0 ± 0.5) S.08 O 3 (0.25 ± 0.02) (5.4 ± 0.7) O 4 (0.03 ± 0.01) (3.8 ± 0.8) O 5 (0.02 ± 0.01) (3.3 ± 0.8) O 3 (0.05 ± 0.02) (4.8 ± 0.4) de Barros et al., in press

19 The dissociation cross-sections due to 4 projectiles at different energies are determined, assuming validity of the d ~ S e 2/3 power law. 10 O d = a S e 2/3 136 Xe MeV d x cm 2 ) 1 H MeV He MeV N MeV S e (ev / atoms/cm 2 ) INTERNATIONAL SYMPOSIUM AND WORKSHOP ON ASTROCHEMISTRY ISWA Campinas July 2016

20 Summary Our experiments demonstrate that 1.5 MeV ion irradiation of nitrous oxide with H + leads to production of molecules NO 2, O 2, NO, O 3, O 4, O 5 and O 3 ; The most abundant daughter species are NO 2 and NO; Same results where observed for the He + beam irradiation; The formation and destruction cross sections of both ion beams where determined; For the O matrix, the dependence of the destruction cross section on the stopping power is found to follow a power law, i.e., σ d S e n, where n 2/3. INTERNATIONAL SYMPOSIUM AND WORKSHOP ON ASTROCHEMISTRY ISWA Campinas July 2016

21 Acknowledgments Thank you