Dr Helen Jane Fraser

Dr. Helen Jane Fraser
(h.fraser@phys.strath.ac.uk)
Department of Physics
University of Strathclyde
(HF ubiquitous)…

Not exhaustive
1. Ice + Interstellar = > 600 hits (2005 – 2011)
3. + Ion* = > 157 hits (2005 – 2011)
• Yet not much of this yet filtering through to gas-grain models
(they have a hard enough time already!!)
• Lots of good work – not always angled to make it accessible to
multidisciplinary audience
• Experiments with ions and radicals per see not easy!! (Nor is
theory)
Recent nice (review) papers (with loads of refs in them):
- Ice in space: surface science investigations of the thermal desorption of model interstellar ices
on dust grain analogue surfaces
Burke & Brown, PCCP, 12, issue 23, 5947 – 5969 (2010)
- Ice surface reactions: A key to chemical evolution in space
Watanabe & Kouchi PROGRESS IN SURFACE SCIENCE, 83, issue 10-12, 439 – 489 (2008)
- Reaction Networks for Interstellar Chemical Modelling: Improvements and Challenges
Wakelam, et al. SPACE SCIENCE REVIEWS, 156, Issue: 1-4, 13-72 (2010)
-The Spitzer Ice Legacy
Oberg et al ApJ (2011) 2011arXiv1107.5825O

Role of Ice
in “Star
and Planet
Formation”

Icy Grains in Protostellar Envelopes
Credit: NASA/JPL-Caltech/R. Hurt (SSC)

Figure 1; This image from NASA's Spitzer Space Telescope shows the
"mountains" of gas and dust in a dense molecular cloud where stars are born.
Dubbed "Mountains of Creation" by Spitzer scientists, these towering “peaks”
are illuminated at their tips with light from warm, embryonic stars, and packed
full of molecules, atoms and ions. Credit; Image courtesy of NASA/JPL-Caltech/L. Allen
(Harvard-Smithsonian CfA)
Temperature = 10 K (-263 deg)
Pressure = 10 -18 Bar cf. Earth = 1 Bar

Fraser et al, A&G, 2003

• THERMODYNAMICS
we need enough energy for the
reactants to form products
• KINETICS
We have many millions of years in space
but we need the reactions to occur within
the lifetime of the astronomical object
(and when reagents are available)

• T too low to overcome activation energy barrier
Energy
E a
reactants
T = 10 - 200 K
‘No barrier chemistry’
products
• Molecular density so low that 3 body collisions are rare
(10 6 (max) vs. 10 21 molecules cm -3 )
– ‘all’ collisions should be effective collisions!!
+
+
+

H 2
CO 2
CH 3 OH
H 2 O
List of Detected Cosmic Molecules in
Interstellar and Circumstellar Environments.
CO
http://www.astro.uni-koeln.de/cdms/molecules

Image courtesy of K Pontoppidan

adapted from an original idea in HJ Fraser, MP Collings and MRS McCoustra,
Review of Scientific Instruments, 2002, 73, 2161

Key to
‘large’ molecule
formation
=
WATER ICE & DUST

Complex molecules - do they form in / on ices then
desorb or do we desorb ions / radicals or reactive
molecules and have a post desorption chemistry?
Credit: Y,-J. Kuan, S.B. Charnley, H.-C. Huang,
W.-L. Tseng, Z. Kisiel, Astrophys J. 593, 848 (2003)
glycine
in Orion!
Credit: C.R. O'Dell/Rice University, NASA.
Radio = large molecules
Permanent dipoles

Remote
Observations
Laboratory Experiments
Theoretical
Chemistry
Modelling of
Environment

Observing
Interstellar
Ices

Background star
Proto-star
AKARI / Spitzer / Hershel

Figure courtesy of E van Dishoeck

Realistically – can ONLY claim H 2 O / CO 2 / CO with any confidence
Back out HCOOH / H2CO / CH 3 OH / NH 3 / CH 4 with some confidence
Perhaps get 13 CO 13 CO 2 OCN if present (low s)
ANYTHING ESO-VLT else is ISSAC speculative - and always will be….
Only lab detections or gas phase links (via KNOWN chemical pathways
will tell us for sure) AKARI AOT04
Spitzer - IRS
ISO
ISO
van Dishoeck et al., Pacific-Chem Proceedings (2006)

Ice Structure in Space
• Band profile indicates ice amorphous
• Majority of ice FORMS by
chemical vapour deposition
i.e. H + OH, O 2 + H, H 2 +
O ???
• Only in disks / behind
shocks does it vapour deposit
from gas phase
H 2 O (g) → H 2 O (s)
Watanabe & Kouchi (2008) PSS
• WE DON’T KNOW ANYTHING ELSE
ABOUT water ICE STRUCTURE FROM
OBSERVATIONS OF ICES ALONE

Water Ice
Structure
(synergy with theory)

H 2 O = most abundant
condensed solid in ISM
Al Halabi et. al.
JCP 120, 3358
(2004)
> 180 K
Al Halabi, Fraser
et. al. A&A, 422,
777 (2004)
< 150 –180 K
< 130 K
< 70 K
Ehrenfreund, Fraser, et. al. P&SS, 51, 473 (2003)
McCann Sweatmann & Fraser, JCP (2011) in prep
Fraser & Miller JCP (2011) in prep

Wang et al ApJ ( 2005)

Ice in Space
• catalytic structure for chemistry
• on the ice surface
• & in grain bulk
governed by its structure & hydrogen bonding
…depends on intrinsic properties of ‘local’ environment as ice formed / deposited
Ice has potential e.g. temperature, to be density, a (the) ‘impurities’ KEY tracer
depends on evolution of environment as ISM evolves
of prevailing physical and chemical conditions
(a) as clouds form, evolve & form stars & planets
• ‘glue-like’ properties from bulk porosity
(b) biological haven
• changes electrostatics
(c) chemical nano-factory
• leads to grain sticking and aggregation in planet building
Ice is the controlling reservoir of molecules in SFR
governed by its structure & hydrogen bonding
to/from the gas phase, thereby intrinsically
linked to our OTHER tracers / probes of SF
…depends on intrinsic properties of ‘local’ environment as ice formed / deposited
e.g. temperature, density, ‘impurities’
depends on evolution of environment as ISM evolves

Synergy with
the Laboratory

Solid-State Astrochemistry
10 7 pre-stellar
10 7 star formation
10 6 – 10 7 planet formation
…then we have a solar system
1 expt = 12 –48 hr
Image Credit: A. Caulet(ST-ECF, ESA) and NASA
Astronomy
small grains
P < 10 -10 – 10 -15 mbar
(dominated by H 2 then CO)
T grain = 10 – 300 K
T gas = 10 – 1000 K
1 Lyman α / Lyman-Werner band UV photon
per 10 6 years per grain
1 atom / molecule – grain collision per 10 4 years
1 X-Ray / CR ‘direct hit’ per 10 5 years
Surface Science
To date = defined surfaces
P < 10 -10 mbar
(also dominated by H 2 then CO)
T grain = 10 – 450 K
T gas = 100 - 300 K
1 Lyman α / Lyman-Werner band UV photon
per molecule per second!! (≈ 5 sec ≅ ISM)
@ 1 L (Langmuir) dose = 10 15 molec cm -2 s -1
1 X-Ray / CR ….

Why is there such a large degree
Establish the reaction kinetics & reaction mechanism
Analyse competing reaction pathways & product yields
of chemical
Predict how similar
complexity?
reactions proceed
What effects do solid state chemical
Measure sticking probabilities / binding energies
reactions Understand have how on the the physical evolution properties of star
of the grain/ ice affect the chemistry
Identify dominant processes in different physical environments
forming environments?
How can chemistry help us to
Solid-state probe and tracer species
understand Historical the map physical of physcial environments
conditions
we are observing?

• What does astronomy need?
Solid-State Astrochemistry
• data
i.e.
sticking probability S(θ)
Astronomy
control initial state…
binding energy E des
observe final state
(assuming E ads = E des = BE)
• understanding “how to apply data”
i.e. all the above may be f (T grain , θ….)
(NOT ALWAYS A SIMPLE NUMBER)
• understanding importance of KINETICS
as well as THERMODYNAMICS
Surface
Science
Determine values empirically &
accurately
• Numbers
[x product , x reagent ] = ƒ (t, P, T, θ…)
OH
Cosmic
Rays
CO 2 carbon
CO or silicate
based
H 2 CO
CH 3 OH
H 2 O
NH 3
N
H
H 2
O
hν
QMS
probe gas ϕ
IR-RAIRS
H 2 CO
CH 3 OH
hν
CO
substrate
OH
H N
O
H 2 O
probe
surface
species
10 nm – 10 µm
1 - 3 cm
Fraser, Collings & McCoustra, Rev. Sci. Inst. 73, no.5, 2161 (2002); Fraser & Van Dishoeck, ASR, 33, 14 (2004)

Solid-State Astrochemistry Labs
Spectroscopy
Mid- NIR
HV (10 -6 )
Trans-FTIR
Spectra (cf. directly to obs)
A-values (∫I(ν)→no. of molecules)
Leiden (van Dishoeck, Linnartz)
Birmingham, AL (Gerrakines)
NASA Ames (Allamandola, Sandford)
Cataina (Palumbo)
Desorption / Scattering
Thermal / UV
Electron / collision
UHV (10 -10 )
TPD / RAIRS
Reactivity
HV + UHV
TPD/RAIRS/STM
hν / electron / atom
trans-FTIR + HPLC
Kinetic & thermodynamic data
Quantum yield
(direct to models & interpretation of obs)
Fraser (Strathclyde), Brown (UCL), McCoustra (HW), Leiden (van Dishoeck),
Kaiser (Hawaii), Sitz (Austin), Martin (Marseille), Kay, Kimmel (PNWL)
THEORY [Fraser (Strathclyde), Leiden (van Dishoeck, Kroes),
Darling (Liverpool)]
Energy Partition
Reaction rates & branching ratios
Quantum yield, isotopic effects
(direct to models & interpretation of obs)
UHV: Leiden (van Dishoeck, Linnartz), McCoustra (HW), Fraser (Strathclyde), Lemaire
(Cergy), Hiraoka (Japan), Watanabe (Japan), Barrigola (Virginia), Mason (OU)
H2 – Pirronello (Cataina), Vidali (Syracuse), Lemaire (Cergy), Hornekaer (Aarhus), Price
(UCL) HV: - more historic – Gerrakines, Ehrenfreund, Allamandola, Sandford, Schutte
- recent – Bernstein, Dartois, Munoz-Caro, Palumbo (Cataina)

Overview
1. Physical Processes
Desorption, trapping, ice structure, H-bonding
2. Chemical Processes
Surface chemical reactions, hν vs. electron vs. atom-molecule,
3. Complex Chemistry
Deuteration, ‘bio-molecules’, ions & radicals, where next?

Desorption
+ Trapping
e.g. H 2 O + CO

a) COporous
ASW
CO in multilayer CO on internal / external H 2 O surfaces
2139 cm -1
CO at H 2 O-CO
interface
2152 cm -1 & 2139 cm -1
b) COcompact
ASW
2152 cm -1 & 2139 cm -1 CO inside ice
(trapped in collapsed pores)
2136 cm -1
CO in multilayer
CO at external H 2 O surface
2139 cm -1
2152 cm -1 & 2139 cm -1 No CO
CO at H 2 O-CO
interface
2152 cm -1 & 2139 cm -1
c) CO-
I c
CO in multilayer
2139 cm -1 No CO No CO
CO at H 2 O-CO
interface
2152 cm -1 & 2139 cm -1
d) mixed
CO-H 2 O Ice
CO on internal / external H 2 O surfaces CO on internal / external H 2 O surfaces
2152 cm -1 & 2139 cm -1 2152 cm -1 & 2139 cm -1
CO inside ice
(trapped in collapsed pores)
2136 cm -1
Substrate
Temperature (K)
8 30
80
Fraser et al. MNRAS, 353, 59 (2004)

Implementing the Kinetic Model in Astrochemistry
+
1 K / 10 3 yr
1 K / 10 2 yr
1 K / 10 yr
1 K / yr
no desorption
from
ice surface
from
‘in’ ice
desorption
single step
no discrimination
between
ASW & Ic
desorption
from CO
overlayer
1 K / 10 3 yr
1 K / 10 2 yr
1 K / 10 yr
1 K / yr

Chemical Reactivity

e.g. H 2 O formation
Hiraoka (1998) [O in N 2 O]
‘Holy Grail’
How astrophysically
relevant are the
conditions?

Miyauchi et al CPL (2008), Ioppolo et al ApJ (2008, 2010), Dulieu et al JCP (2008, 2010, 2011)…..
Japanese + Ledien group – RAIRS
French Group TPD + RAIRS

Miyauchi et al CPL (2008), Ioppolo et al ApJ (2008, 2010), Dulieu et al JCP (2008, 2010, 2011)…..
• all produce H 2 O (D 2 O / HDO)
• all O 2 + H (D) [ 18 -O]
• all produce significant H 2 O 2 , O 3
Is O 2 dominant in
cloud edges?
Is it frozen out?
Hard to make GROUND STATE OH radicals
neither detected
in ISM ices
HARD to do experiments on ice + ions or radicals

Deuteration
The HDO/H 2 O abundance ratio =
key diagnostic of the evolution of water
during the star- and planet-formation process
& its origin on Earth.
Link to OH / OD [H/D ratio] during H 2 O formation

Deuterium fractionation on dust
D
H
O
Surface reactions produce
the following molecules:
H 2 CO, HDCO, D 2 CO??
DUST
NH 3 , NH 2 D, ND 2 H, ND 3
CH 3 OH, CH 3 OD
CH 2 DOH, CHD 2 OH
CH 2 DOD, CHD 2 OD
CD 3 OH, CD 3 OD
CO
H 2 O, HDO, D 2 O,
H 2 , HD, D 2
Tielens 1983; Charnley et al. 1997; Caselli et al. 2002, P&SS

CO freezes out in
v. dense ISM
regions
(where H 2 and HD
dominate – not H/
D)
H 2 CO –
underproduced cf.
ISM gas phase
abundances
CH 3 OH formation
Route from HCO /
DCO to HCOOH
still unclear
though HCOOH
detected in ices
D into CH groups – can occur gas / surface
D into OH groups??? D into NH groups??
CH 3 OH – can be
made @ rate
comensurate
with reproducing
ISM gas phase
abundances
Also detect OH (NEVER OD – why?)
H 3 0 + but NOT D 3 O + why?
Watanabe et al. (2005) IAU Proc.

Interesting Papers
on Solids & Ions..
• Title: Formation of H(2)(+) by Ultra-Low-Energy Collisions of Protons with Water Ice
Surfaces
Author(s): Bag Soumabha; McCoustra Martin R. S.; Pradeep T.
Source: JOURNAL OF PHYSICAL CHEMISTRY C Volume: 115 Issue: 28 Pages:
13813-13819 DOI: 10.1021/jp203310k Published: JUL 21 2011
• CO(2) FORMATION IN QUIESCENT CLOUDS: AN EXPERIMENTAL STUDY OF THE
CO plus OH PATHWAY
Author(s): Noble J. A.; Dulieu F.; Congiu E.; et al.
Source: ASTROPHYSICAL JOURNAL Volume: 735 Issue: 2 Article Number: 121
DOI: 10.1088/0004-637X/735/2/121 Published: JUL 10 2011
• Title: Kinetics of the OCN(-) and HOCN formation from the HNCO + H(2)O thermal
reaction in interstellar ice analogs
Author(s): Theule P.; Duvernay F.; Ilmane A.; et al.
Source: ASTRONOMY & ASTROPHYSICS Volume: 530 Article Number: A96 DOI:
10.1051/0004-6361/201016051 Published: JUN 2011
• Title: Photochemistry of polycyclic aromatic hydrocarbons in cosmic water ice II. Near
UV/VIS spectroscopy and ionization rates
Author(s): Bouwman J.; Cuppen H. M.; Steglich M.; et al.
Source: ASTRONOMY & ASTROPHYSICS Volume: 529 Article Number: A46 DOI:
10.1051/0004-6361/201015762 Published: MAY 2011

Key ?
1. From an astronomy perspective
3. From a chemistry perspective
5. Recombining Both

Observational Prospects
Now:
AKARI / SPITZER
IR absorption features of ices / gas phase data
Very Now:
Hershel / ALMA
Gas phase observations, high resolution, high spatial definition
but INFERS GAS PHASE by working backwards
Wished for now:
JWST (MIRI) / SPICA (SAFARI)
Gas and ices co-observed high resolution & high spatial
definition

The Spitzer Ice Legacy…
Oberg et al ApJ in press (2011)

The Hershel Legacy…
Goldsmith et al ApJ (in press)
O 2 ….. H 2 O… H 2 O +
Johnstone et al ApJ (in press)
Kristensen et al A&A (2011)
Neufield et al ApJ (2010)

Future Ice Observations
Large scale = ice mapping cf. solid state material
distribution with other astronomical observables
e.g. Noble et al (2011) Sonnentrucker et al ApJ(2009), Pontoppidan et al A&A (2006)
(images courtesy K. Pontoppidan)
small scale =
resolving snow lines
in disks / seeing ice
in disks
e.g. Pontoppidan et al A&A (2004), Oberg et al ApJ in press (2011)

known unknowns and unknown unknowns …
Can we back out surface chemistry from gas phase observations?
Model should reproduce lab (show controlled process)
then use same model on astro timescales
Disentangle what lab shows and theory can tell us
from what astrochemistry needs (what is good enough)
What are concrete observational tests of ice chemistry /
ice desorption/ gas-ice coupling?
What is the test molecule x that is ‘complex’ and ONLY made in solid phase?
What are the key set of surface reactions?
What data is needed in a database?
Thermal desorption of single / bi components understood
but what about multilple components? larger molecules?
What about ions radicals sputtering?
How to model ice / monolayer //do the underlying surfaces matter?
Bulk vs small grain effects on surfaces + morphology

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