M. Cueto, M. Jiménez-Redondo, V.J. Herrero, J. L. Doménech, J

M. Cueto, M. Jiménez‐Redondo, V.J. Herrero, J. L. Doménech, J. Cernicharo
Inst. Estructura de la Materia, CSIC, Spain
Funding: CSD2009‐00038 “ASTROMOL”, FIS2010‐16455
2
1. Introduction
2. Kinetics of Cold Plasmas of H2 + Simple Gases of interest to Interstellar Media (ISM).
3. Spectroscopy in the Laboratory and detection in Space of Ions of Astrophysical Interest.
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Interest of cold plasmas with high H2 content
• Plasma‐Wall Interaction in Nuclear Fusion Reactors
This talk
• Thin Film Processing (microelectronics, solar cells…)
• Chemistry of Interstellar Media (ISM) & Planet Atmospheres
Hydrogen: the main constituent of Universe!
Periodic Table of Astronomers
H 75%
He 23%
O 1%
C 0.5%
N 0.1% …
Ar 0.02%... 4
 180 molecular species detected till now in space:
•
•
•
•
•
Simple radicals (OH, NH…)
Diatomic molecules (H2, HD, O2, N2…)
Polyatomic species (H2O, D2O, NH3…)
Protonated ions (H3+, H2D+, N2H+, H3O+…)
Complex species (amino acids, C60… )
http://www.astrochymist.org/astrochymist_mole.html
actualized list of the species found
Molecules play key roles in the Generation of New Stars in Interstellar Molecular Clouds
5
• MOLECULAR IONS can be neutralized
much more efficiently than ATOMIC IONS.
Through dissociative neutralizations:
AB+ + e  A + B, they decouple the gas
from any electro‐magnetic field.
The Horsehead Nebula, dark molecular cloud in Orion
• MOLECULES cool efficiently the gas
heated by gravity collapse, thanks to
their large number of energy levels,
many more than ATOMS, allowing very
efficient absorption and emission of
radiation.
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Electro‐Magnetic Spectrum
e‐ + e+ annihilation
(0.5 MeV, 4 nm)
Cosmic background 2.7 K (0.2 meV, 1 mm)
MW
Molecular
Transitions

Electronic
Vib‐Rotational
Rotational
Cold ISM Regions
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Spectral transmittance of dark Molecular Clouds
Composed mainly of H2 and Dust (1%)
Barnard 68
T  16 K
UV ‐ visible
( large dust opacity )
Infrared ‐ Radio waves
( good transparency )
Most appropriate for molecular detection !
8
Cold H2 rich lab plasmas vs. ISM Molecular Clouds
Similarities
• Gas‐phase dominated by H2
• Low ionization degree • Low density  only binary collisions
• Extensive ion‐molecule chemistry (large k  f(Tgas))
• The lack of three body reactions implies that surface chemistry
is crucial to explain the formation of molecules like H2
9
Cold H2 rich lab plasmas vs. ISM Molecular Clouds
Differences
• Ionization mechanisms: Lab: electron impact Molec. Clouds: cosmic rays • Neutralizations of ions : Lab: neutralization in the wall
Molec. Clouds: dissociative electron attachment
• Surface chemistry: Different relevance of the different possible processes, such as Langmuir‐Hinshelwood, Eley‐Rideal…
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2. Kinetics of Cold Plasmas rich in H2 of interest to Interstellar Media (ISM).
Electric discharges studied:
H2 , H2 + N2 , H2 + O2 , H2 + Air , H2 + Ar
11
Experimental details
HOLLOW CATHODE DISCHARGES
•
•
•
•
Low Pressure  0.7 ‐ 20 Pa
Low ionization degree  10‐5
Te  3 ‐ 8 eV ( > 104 K )
Tgas (neutrals & ions)  300 K
Tanarro et al., JPC. A 111, 9003 (2007) Jiménez‐Redondo et al, PSST, 22,25022(2013)
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Kinetic Models
Main Processes Considered: •
Ionization + dissociation by electron impact in the glow
• Gas phase ion‐molecule reactions
• Surface recombination of neutrals and ion neutralizations
• Zero order models, 2 volumes: negative glow + cathode sheath • Set of time dependent differential equations for neutrals and ions
• Maxwellian electron energy distributions
14
H2 lab. plasmas: Neutrals
-3
Concentration (x 10 cm )
2
0.08 mbar
15
Experiment
Model
1
H2
H
0
1
2
Mass (a.m.u)
Méndez et al, JCP A 110, 6060 (2006)
[H2] / [H]  85 ‐ 90 %
Balance [H2 ]  [H] : Dissociation  Wall Recombination
Very efficient H2 dissociation,
with large rate coefficients 
Strong recycling of H2 in the walls must occur !
15
H/H2 balance in Space
Unexpectedly large concentration of H2 molecules in molecular clouds: (H2 / H  10 4)  H2 formation on dust surfaces. Dust  1%
dust
particle
ISM dust surfaces slightly covered with atoms  Langmuir‐Hinshelwood recombination, i.e., atoms adsorbed on the surfaces migrate until they meet another one and react.
Laboratory plasmas: high surface coverage 
Eley‐Rideal mechanisms prevail, i.e., one atom reaches the surface, meets another atom and reacts.
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Hydrogen lab. Plasmas: Ions
Inversion of the Major Ion from H2+ to H3+ ( with Pgas   Te  )
+
0.5
Symbols: Exper.
Lines : Model
+
H2
0
1
+
H
3
H2 (Pa)
10
3 -1
H3
+
H2 H2H3+ H
+
k (cm s )
Relative Ion Conc.
1
-9
10

+

7
8
H2+e H2+2e
-10
10
4
5
6
T
Balance H2+ / H3+ : H2 + e  H2+ + 2e  H2+ + H2  H3+ + H
Méndez et al, JCP A 110, 6060 (2006)
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H3+ in Space
•
Second most abundantly produced interstellar species, next to H2.
H2 + Cosmic Rays H2+ + e
•
H2+ + H2  H3+ + H
Starts a chain of barrier‐less protonation reactions to form new species, like water: H3+ + O → OH+ + H2 …… H3O+ + e  H2O + H
H3+ IR spectrum in lab: Oka (1980)
H3+ in Jupiter Ionosphere:
Oka & Geballe (1990)
H3+ in ISM: Geballe & Oka (1996)
H2+ not yet detected in ISM !
Ions:
Protonated ions prevail over the parent ones: NH4+, increases markedly with NH3 content.
H3+ + NH3  NH4+ + H2
N2H++ NH3  NH4+ + N2 …
Carrasco et al. PCCP, 13, 19561 (2011)
Relative concentration
Neutrals:
NH3 : Minor stable product ( 2%),
produced by wall reactions involving H,
N, NH & NH2 in several steps.
8 Pa, H2+ (% variable) N2
0
10
Neutrals
H2
-1
N2
10
NH3
-2
10
0.00
0.6
Relative concentration
H2 + N2 lab. plasmas
18
0.03
0.5
0.06
0.09
0.12
+
NH4
0.4
0.3
N 2H
0.2
H3
+
+
0.1
Protonated ions
0.0
0.00
0.03
0.06
0.09
0.12
Fraction of N2 (discharge off)
(H2 + O2) 8 Pa
H2 + O2 plasmas
Neutrals :
• H2O, formed at the walls, more abundant than the O2 precursor.
0
10
Relative concentration
See posters session: P‐27 !
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-1
10
H2
H2O
O2
-2
10
Neutrals
0.00
0.03
0.06
0.09
0.12
0.15
0.8
• H3O+ always dominant.
• Hardly any O2H+ is detected.
Carrasco et al., Plasma Phys. Contr. Fusion, 54, 124019 (2012) 0.7
Relative concentration
Ions :
H 3O
+
0.4
Protonated ions
0.3
+
0.2
H3
0.1
0.0
0.00
O 2H
0.03
+
0.06
0.09
0.12
0.15
Fraction of O2 (with discharge off)
NH4+ &
H3
O+
in Space
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T (K)
400
200
NH4+
100
30
H3O+
Protostar envelope, static model, 105 years after “switch on” of a protostar.
Rodgers & Charnley, ApJ 585, 355 (2003)
Distance to star center (cm)
NH4+ and H3O+ predominate as their neutral precursors, NH3 and H2O, evaporate from the dust surfaces (ISM : H2O / H2  10‐5, NH3 / H2  10‐7)
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• NH3 slightly lower than H2O
in spite of [N2]/[O2]  4
• NH3 needs more formation steps in the walls
Ions
+
• NH4 clearly dominates when NH3
reaches enough concentration.
Relative concentration
Neutrals
0
10
H2
-1
10
N2
H2O
NH3
-2
0.06
0.09
O2
0.12
0.15
0.18
0.6
+
NH4
0.5
0.4
Protonated ions
0.3
+
H3O
0.2
+
H3
+
0.1
Carrasco et al., Plasma Phys. Contr. Fusion, 54, 124019 (2012) Neutrals
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0.03
Relative concentration
H2 + Air plasmas
(H2 + Air) 8 Pa
0.0
N2H
0.03
0.06
0.09
0.12
0.15
0.18
Fraction of air (with discharge off)
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Hierarchy of protonated ions
NH3
0.6
Proton affinity (kJ mol‐1)
Protonated ion
853.6
NH4+
H3
O+
H2O
691
N2
493.8
N2H+
H2
422.3
H3 +
+
O2
421
HO2
Ar
371
ArH+
+
NH4
0.5
Relative concentration
Molecule (H2 + Air) 8 Pa
8 Pa
H2 + % Air
0.4
+
H3O
0.3
+
0.2
H3
0.1
N2H
0.0
+
HO2
+
0.03 0.06 0.09 0.12 0.15 0.18
Fraction of air (with discharge off)
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H2 + Ar lab. plasmas (H2 + 15 % Ar) 2 Pa
Ions
Ar + H2+  ArH+ + H Ar + H3+  ArH+ + H2
ArH++ H2  Ar + H2+
Relative Ion Current
• H3+ is the major ion.
• ArH+ > Ar+  balance of reactions:
1
+
+
H3
H H+
2
ArH
+
0.1
Ar
0.01
1
2
+
40 41
3
Ion mass
Méndez et al., PCCP. 12,4239 (2010) 24
ArH+ in Space
First detection of 36ArH+ (and of any noble gas molecule) in Space,
Herschel Space Observatory (December 2013), 36ArH+ rotational transitions. 36ArH+,
J=1-0
617.5 GHz
36ArH+,
J=2-1
1243.6 GHz
Barlow et al, Science,342,1343 (2013) Crab Nebula: from supernova explosion observed in China in 1054 AD. 36Ar formed by ‐particle capture chain.
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• Unfortunately, the Herschel mission ended in
spring 2013.
• The Earth atmosphere presents a high opacity
for those 36ArH+ rotational transitions.

Herschel Telescope
Future searches for 36ArH+ will rely in
ground‐based INFRARED observations. CRIRES (CRyogenic high‐resolution
InfraRed Echelle Spectrograp) ESO.
Atacama, Chile.
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3 ‐ Spectroscopy in Laboratory and detection in Space of Ions of Astrophysical Interest : ArH+ & NH4+ isotopologes
Experimental set‐up for IR absorption of ions by difference frequency laser spectroscopy in our lab
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ArH+ IR spectroscopy
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signal / V
40
6
0.10
R(6)
+
ArH
 = 1-0
0.08
R(6)
40
40ArH+ : +
ArH
 = 2-1
Signal / Noise  1000 0.06
at  = 1‐0 , with a single scan.
4
0.04
2
[40ArH+]  3 x 1010 cm‐1
0.02
Kinetic temp.: 390  10 K 0
2711.39
2711.40
2711.41
2587.72
2587.73
-1
2587.74
2587.75
wavenumber / cm
Solar wind composition: 40Ar/ 38Ar/ 36Ar = 0.0 / 15.0 / 85.0 %
Earth’s atmosphere comp.: 40Ar/ 38Ar/ 36Ar = 99.6 / 0.06 / 0.34 %
40Ar:


Product of 40K decay, ½ = 1.25 × 109 y.
IR spectra of 19 vib‐rotational lines of 36ArH+
and 38ArH+
obtained,
only 8 measured before in labs, with worse resolution. 36ArH+
38ArH+
100 averages
800 averages
108 cm‐1
2 x 107 cm‐1
M. Cueto et al, ApJL. 783:L5 (2014)
The data have also been used in a Dunham‐type global fit of all published laboratory data (IR and sub‐mm) of all isotopologues.
Exposure time at CRIRES granted by ESO
to find out the 36ArH+/38ArH+ ratio in Crab Nebula
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Ammonium Ion Spectroscopy
Unfortunately, the tetrahedric symmetry of NH4+ precludes its observation in radio frequencies. NH4+
NH3D+
However, the isotopic variant NH3D+, with small permanent dipole moment ( = 0.26 D), is a good candidate for radio‐astronomical searches.
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Deuterium enrichment in Space
In spite of the cosmic ratio D/H  10‐5 ! , deuterated molecules are abundantly found in cold ISM regions (T < 20 K),
due to the “Zero Point Energy” effect initiated by H3+
B1‐bS dark cloud (12 K) X+ / H2
NH4+
NH3D+
( NH3D+ / NH4+ ) ratio remarkably enhanced
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Energy
Zero point energy effect
The lowest vibrational level is closer to the minimum of the potential curve as the isotope composition increases in weight
Internuclear distance
IRAM 30m radio‐telescope surveys of NH3D+ in Sierra Nevada, Granada (Spain)
• Orion IRc2: proto‐star region • Perseo B1‐bS: cold pre‐stellar core Orion
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35
Orion IRc2 survey Perseo B1‐bS survey TGAS  100 K
TGAS  12 K
U-262816.7
U-262816.73
262807
Unassigned peak found close to the predicted frequency for NH3D, Jk (10‐00) = 262807  9 MHz ( 3) (Nakanaga & Amano 1986) IR spectrum of NH3D+ + *NH4+
in 30 Pa (NH3 (30%) + D2) discharge
Levels involved in the
4 IR band of NH3D+
2
J
1
0
K=0
10 – 00 pure rotational transition
Orion survey: mm spectrum
36
37
Cernicharo et al, ApJ. 771, L10 (2013)
Domenech et al, ApJ. 771, L11 (2013)
New Predicted Jk (10‐00) = 262817  6 MHz (3)
NH3D+, exact matching!
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Conclusions
•
Neutral products like HD, NH3 or H2O are efficiently formed in reactor
surfaces for the rich H2 containing mixtures of the plasmas studied.
•
The ion chemistry is dominated by very efficient protonation reactions,
in analogy with the interstellar medium.
•
The preponderance of a given ion is largely given by the proton affinity of
its neutral precursor.
•
•
The new IR data of 36ArH+ and 38ArH+ should help in future ISM searches.
Thanks to the new laboratory data, the ammonium ion (NH3D+) has been
detected for the first time in the ISM.
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Thank you!

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