LAMAp/LERMA, UMR 8112 du CNRS, Observatoire de Paris

Université de Cergy-Pontoise, FRANCE

Water formation through O2+D pathway on cold silicates

and amorphous water surfaces of interstellar interest

Marco. Minissale, François. Dulieu, Emanuele. Congiu, Saoud Baouche.

Giulio. Manicò, Mario. Accolla, Valerio. Pirronello Dipartimento di Fisica ed Astronomia Università degli Studi di Catania, ITALY Dipartimento di Scienze Applicate – Università Parthenope Napoli, ITALY

Henda. Chaabouni

119 th International Vacuum Congress. Paris, 11/09/2013

2

OutlineBackground : Water in the interstellar medium

Experiments

Results:

1- Reflection Absorption Infrared Spectroscopy (RAIRS) and Temperature Programmed Desorption (TPD) analysis of water formation through O2+D pathway on:

- Silicate surfaces - Solid water ices

2- Chemical desorption process of water product

3- Kinetic model for the O2+D reaction during thermal processing

Conclusions Cost meeting, 2 nd- 5 th April 2013

The Chemical Cosmos, 2 nd- 5 th April 2013

3

Detected in the ISM and outside of our Solar System as Gas, and Ice.

Abundant in the Cosmos and the Solar System (planets, comets…).

Star formation region

Gas H2O: 3 × 10−8

Gas H2O: 10−7−10−6

Background Water in in the ISM

Tgas= 50-100K

Tdust= 10 K

Tdust =Tgas= 10 K

Tgas= 10 K

4

Background

Miyauchi et al. Chem.Phys.Lett (2008)

Ioppolo et al. ApJ (2007), PCCP (2010)

Cuppen et al. PCCP (2010)

Previous studies

H + O OH

H + OH H2O

H + O2 HO2

H + HO2 H2O2

H + H2O2 H2O + OH

H + OH H2O

H + O3 O2 + OH

H + O2 HO2

H + HO2 H2O2

H + H2O2 H2O +OH

H+ OH H2O

H2+OH H2O +H

Efficient formation of H2O and H2O2 ices at 10 K-28 K in the Multi-layer regime

10- 30 layers of solid O2 ice

19 th International Vacuum Congress.

Gas-surface reactions for water formation in the ISM

(JAPAN)

(LEIDEN)

H2O2 / H2O > 1

Paris, 11/09/2013

(CERGY + LEIDEN)

(CERGY +USA)

Tielens & Hagen (1982)

5

The present work

O2+D pathway in the Sub-monolayer regime Amorphous SILICATE Amorphous H2O water ices

(~100 nm) film of Olivine (MgxFe 1−x)2SiO4 Thickness~10 Monolayers

Tsurface =10 K

(Bare dust) (Icy Mantle)

0<x<1

19 th International Vacuum Congress.

Paris, 11/09/2013

QMS

Micro-wave discharge

D diss (D2)=70 % Tgas=300 K=3.0×1012 molecules.cm-2.s-1

O2 (≤ 1 ML)

Temperature Programmed Desorption (TPD)

Tsurface=10 K- 220 K

Heating rate = 0.04K/s

(Gas phase detection) Cryocooler 5 K- 350 K

FT-IR

Spectrometer Bruker tensor 27

Reflection Absorption Infra-Red Spectroscopy (RAIRS)

(Insitu Solid phase detection)

MIR: (4000- 600) cm-1

Cryocooler 5 K- 350 K

Experiments

Sample (siliacte, water)Tsurface= 10 K

619 th International Vacuum Congress.

QMS

Triply differentially pumped beam-lines

FORMOLISM set-up, (LERMA/LAMAP, Cergy)

(MCT) Detector

10-11 mbar

83°

Quadrupole Mass Spectrometer QMS

UHV chamber

Paris, 11/09/2013

Result 1: Water formation on amorphous Silicates

Chaabouni et al. J. Chem. Phys (2012)719 th International Vacuum Congress.

RAIR specrta

n (-OD)

Successive deposition on silicate at 10K

1 min (0.18 ML) O2 + 4 min (0.65 ML) D-atoms

(1 O2 + 4 D 2 D2O )

Low surface coverages

RAIRS

Silicate at 10 K

In

tegr

ated

are

as

a)b)

c)d)e)

f)

g)(2 6)n

D2O / D2O2 5

D2O2 / D2O < 1

Sub-monolayer regime

Paris, 11/09/2013

~ 1 ML D2O ice

Inte

grat

ed a

reas

O2 exposure dose (ML)

(D2O + D2O2) at 2404 cm-1

D2O2 at 2107 cm-1

0 1 2 3 4 5 6 7 8 9 0.200

0.150

0.100

0.050

0.00

Result 2: Effect of the substrate on water formation

1 ML (O2) + 24 min (D) / Silicate surface at 10 K 1 ML (O2) + 24 min (D) / Porous ASW H2O ice surface at 10 K 1 ML (O2) + 24 min (D) / Non-porous ASW H2O ice surface (prépared at 120 K, cooled to10K)

~ 18 % (D2O) ~ 50 % (D2O) ~ 68 % (D2O)

Low formation yield of D2O water ice on Silicate at 10K

Exposure

819 th International Vacuum Congress.

D2O >> D2O2

(TPD) , Ts= [10 K – 220 K](RAIRS) , Ts=10 K

D2O

~ 5 % (O2) ~ 18 % (O2) ~ 2 % (O2)

Paris, 11/09/2013

9

RESULTS 3: The chemical desorption of water molecules

Chemical desorption of D2O moleculesupon formation on the surface at 10 K

1- Substrate : Silicate2- Exposure of 1 ML of O2 on the surface

3- QMS placed close to the surface

4- Monitoring with the QMS the species desorbing into the gas phase during the exposure of D-atoms on O2 ice at 10 K.

Surface at 10 K

QMS

D

1 ML O2

D2 , D2O gasD2O gas

19 th International Vacuum Congress. Paris, 11/09/2013

Dulieu et al, Sci.Rep . 2013

Reactions routes for water formationSilicates

Ts =10 K

D2O water formation through the barrierless reaction

D + OD D2O

H= -1600 meV

D + OD D2O

Ebarrier=2000 K Chemical desorption of D2O by the exothermic reaction

H= -3700 meV

H=- 3100 meV

H= - 5200 meV 2 D

H= - 5200 meV

OD+OD

D

H= - 2400 meV H= - 4900 meV

Eley-Readel mechanism

1019 th International Vacuum Congress.

Dulieu et al, Sci.Rep . (2013)

Paris, 11/09/2013

Chaabouni et al. J. Chem. Phys (2012)

Cuppen et al. PCCP (2010)

Thermal desorption Kinetic O2+D reaction on Silicates

Exposure 1 ML (O2 ) + X (0 min) of D atoms (6 min) (12 min) (24 min)

(35 min)

1 ML O2+ 6 min D

1 ML O2+9 min

1 ML O2+12 min D

1 ML O2+24 min D

1 ML O2+ 9 min

1 ML O2+12 min D

1 ML O2+24min D

(M 36)

19 th International Vacuum Congress.

1 ML O2+ 6 min D

1 ML O2+ 12 min

1 ML O2+24min D

1 ML O2+35 min D

1 ML O2+ 12 min

1 ML O2+24 min D

1 ML O2+35 min D

1 ML O2+ 6 min D(M 32) (M 20)

(M 36)

(QMS)

TS= 10 220 K

D

11Paris, 11/09/2013

TPD

eV

Modeling Kinetic O2+D reaction on Silicates

H2O(g)

Chemical desorption rate of D2O

O2+ D O2D

O2D +D OD + OD =0,7

D2O2 1-=0,3

D2O2 +D D2O(solid) + OD

OD + D D2O(solid)

Branching ratio of the reaction

Rate constant of reaction with a Barrier

Rate constante of reactions without Barrier

k

k1

k

k

k

1219 th International Vacuum Congress.

D2O(gas)(~ 86 %)

(TPD Experiments)

Paris, 11/09/2013

(MODEL)

13

Conclusions The O2+D reaction is efficient in the sub-monolayer regime at 10 K (D2O >> D2O2) The formation yield of D2O water ice depends on the grain surfaces.

Silicate: OD + D D2O OD + D D2O

Water ices: O2 + D DO2 + D OD +OD D2O2 D2O (solid) + OD

The formation of the first monolayer of water ice on bare dust silicates requires very long timescales to be grown ( >105 years ).

The chemical desorption of water has an impact on the gas phase composition of astrophysical environment, and can affect Stars and Planets formation.

D

19 th International Vacuum Congress.

O2 + D DO2 + D

Astrophysical implications:

Paris, 11/09/2013

High chemical desorption rate of D2O water molecules (~ 90 % ) through the exothermic OD + D reaction.

gas

19 th International Vacuum Congress. 14

Acknowledgments

Université de Cergy(LAMAp/LERMA Laboratory)

Francois DulieuMarco MinissaleEmanuele CongiuSaoud Baouche

Italy, Catania

Giulio Manicò (Model)Mario AccollaValerio Pirronello

Paris, 11/09/2013

19 th International Vacuum Congress. 15Paris, 11/09/2013

LAMAp/LERMA, UMR 8112 du CNRS, de l’Observatoire de Paris

Université de Cergy Pontoise, France

Water formation through O2+D pathway on cold silicates

and amorphous water surfaces of interstellar interest

Henda. Chaabouni

1619 th International Vacuum Congress. Paris, 11/09/2013

The Chemical Cosmos, 2 nd- 5 th April 2013

17

Detected in the ISM and outside of our Solar System as Gas, and Ice coated onto dusts.

The most Abundant component in the Cosmos and the Solar System (planets, comets…).

Star formation region Gas H2O: 3 × 10−8

Gas H2O: 10−7−10−6

Background Water in in the ISM

Tgas= 50-100K

Tdust= 10 K

Tdust =Tgas= 10 K

Tgas= 10 K

18

Background

Miyauchi et al. Chem.Phys.Lett (2008) Oba et al. ApJ (2009)

Ioppolo et al. ApJ (2007), PCCP (2010)

Cuppen et al. PCCP (2010)

Previous studies

H + O OH

H + OH H2O

H + O2 HO2

H + HO2 H2O2

H + H2O2 H2O + OH

H + OH H2O

H + O3 O2 + OH

H + O2 HO2

H + HO2 H2O2

H + H2O2 H2O +OH

H+ OH H2O

H2+OH H2O +H

Efficient formation of H2O and H2O2 ices at 10 K-28 K in the Multi-layer regime

Thick layers of solid O2

19 th International Vacuum Congress.

Gas-surface reactions for water formation in the ISM (Tielens & Hagen (1982))

(JAPAN)

(LEIDEN)

H2O2 / H2O > 1

Cuppen et al. PCCP (2010) H + HO2 --> OH+OH --> H2O2

Paris, 11/09/2013

19

OutlineBackground : Water in the interstellar medium

Experiments

Results:

1- Reflection Absorption Infrared Spectroscopy (RAIRS) and Temperature Programmed Desorption (TPD) analysis of water formation through O2+D pathway on:

- Silicate surfaces - Solid water ices

2- Chemical desorption process of water product

3- Kinetic model for the O2+D reaction during thermal processing

Conclusions Cost meeting, 2 nd- 5 th April 2013