Ion Irradiation of Astrophysical Ice Analogues

Sun 29Sun 29thth June 2003 June 2003 [email protected]@ucl.ac.uk

Ion Irradiation of Ion Irradiation of Astrophysical Ice Astrophysical Ice

AnaloguesAnalogues

4th Annual LEIF Meeting, Belfast

Anita DawesAnita Dawes


IntroductionIntroduction Not much is known about the mechanisms involved in Not much is known about the mechanisms involved in

solid state chemistry in astrophysical environments.solid state chemistry in astrophysical environments.

Over 120 molecular species have been detected Over 120 molecular species have been detected in spacein space Abundances and formation cannot be explained by gas Abundances and formation cannot be explained by gas

phase chemistryphase chemistry


2 3 4 5 6 7 8 9 10 11H2 C3 c-C3H C5 C5H C6H CH3C3N CH3C4H CH3C5N? HC9N

AlF C2H l-C3H C4H l-H2C4 CH2CHCN HCOOCH3 CH3CH2CN (CH3)2CO

AlCl C2O C3N C4Si C2H4 CH3C2H CH3COOH (CH3)2O NH2CH2COOH ? 12C2 C2S C3O l-C3H2 CH3CN HC5N C7H CH3CH2OH C6H6

CH CH2 C3S c-C3H2 CH3NC NH2CH3 H2C6 HC7N

CH+ HCN C2H2 CH2CN CH3OH HCOCH3 CH2OHCHO C8H 13+CN HCO CH2D

+ ? CH4 CH3SH c-C2H4O HC11N

CO HCO+ HCCN HC3N HC3NH+ CH2CHOH PAHs

CO+ HCS+ HCNH+ HC2NC HC2CHO C60C60++

CP HOC+ HNCO HCOOH NH2CHO

CSi H2O HNCS H2CHN C5N

HCl H2S HOCO+ H2C2O

KCl HNC H2CO H2NCN

NH HNO H2CN HNC3

NO MgCN H2CS SiH4

NS MgNC H3O+ H2COH+

NaCl N2H+ NH3

OH N2O SiC3

PN NaCNSO OCSSO+ SO2

SiN c-SiC2SiO CO2

SiS NH2

CS H3+

HF SiCNSHFeO AlNCAlNC

>120 Interstellar and Circumstellar Molecules>120 Interstellar and Circumstellar Molecules

National Radio Astronomy Observatory

Formic Acid

Acetic Acid

Glycolaldehyde

Benzene

Cyanopolyynes

Glycine ?

http://www.cv.nrao.edu/~awootten/allmols.html


Whittet et.al.A&A 315, L357-L360 (1996)Whittet et.al.A&A 315, L357-L360 (1996)

Ices in Space...Ices in Space...Gibb et.al. ApJ 536, 347-356 (2000)Gibb et.al. ApJ 536, 347-356 (2000)

W33A

SpeciesSpecies EliasElias1616

NGC 7538 NGC 7538 IRS 9IRS 9 GL 7009SGL 7009S W33AW33A GL 2136GL 2136 Sgr A*Sgr A* CometsComets

HH22OO 100 100 100 100 100 100 100

CO CO (total)(total) 25 16 15 8 2 <12 5-30CO CO (polar)(polar) 3 2 - 6 2 - -CO CO (nonpolar)(nonpolar) 22 14 - 2 - - -COCO22 (total)(total) 18 22 21 13 16 14 3-20

COCO22 (polar)(polar) 18 14 - 11 13 14 -

COCO22 (nonpolar)(nonpolar)

<1 8 - 2 3 <1 -

CHCH44 - 2 4 1.5 - 2 1

CHCH33OHOH <3 5 30 18 6 <4 0.3-5

HH22COCO - 4 3 6 3 <3 0.2-1

HCOOHHCOOH - 3 - 7 - 3 0.05OCSOCS <0.2 - 0.2 0.2 - - 0.5NHNH33 9 13 - 15 - 20-30 0.1-1.8

XCNXCN <0.5 1 1.5 3.5 0.3 - 0.01-0.4

Gibb et.al. ApJ 536, Gibb et.al. ApJ 536, 347-356 (2000)347-356 (2000)


PlanetSatellite

Ices

JupiterJupiter IoIo SO2, SO3, H2S?, H2O?

EuropaEuropa H2O, SO2, SH, CO2, CH, XCN, H2O2, H2SO4

GanymedGanymedee

H2O, SO2, SH, CO2, CH, XCN, O2, O3

CallistoCallisto H2O, SO2, SH, CO2, CH, XCN

SaturnSaturn MimasMimas H2O

EnceladusEnceladus H2O

TethysTethys H2O

DioneDione H2O, C, HC, O3

RheaRhea H2O, HC?, O3

HyperionHyperion H2O

IapetusIapetus H2O, C, HC, H2S?

PhoebePhoebe H2O

RingsRings H2O

UranusUranus MirandaMiranda H2O, NH3

ArielAriel H2O, OH?

UmbrielUmbriel H2O

TitaniaTitania H2O, C, HC, OH?

OberonOberon H2O, C, HC, OH?

NeptunNeptunee

TritonTriton N2, CH4, CO, CO2, H2O

PlutoPluto CharonCharon H2O, NH3, NH3 hydrate

N2, CH4, CO, H2O

KBO’sKBO’s H2O, HC-ices (CH4, CH3OH), HC, silicates

Ices in the outer Solar SystemIces in the outer Solar System


IntroductionIntroduction Not much is known about the mechanisms involved in Not much is known about the mechanisms involved in

solid state chemistry in astrophysical environments.solid state chemistry in astrophysical environments.

Over 120 molecular species have been detected Over 120 molecular species have been detected in spacein space Abundances and formation cannot be explained by gas Abundances and formation cannot be explained by gas

phase chemistryphase chemistry

Require laboratory data to understand the Require laboratory data to understand the mechanisms involved in condensed phase mechanisms involved in condensed phase molecular formation/destruction.molecular formation/destruction.

The nature of ices and their processing depends The nature of ices and their processing depends on the environment in which they are found...on the environment in which they are found...


Radiation EnvironmentsRadiation Environments The astrophysical ices can be The astrophysical ices can be broadlybroadly divided into 3 divided into 3

environments:environments: Icy grain mantles in the ISMIcy grain mantles in the ISM

Dense clouds: Dense clouds: Lyman-Lyman-, cosmic rays, cosmic rays Cold diffuse clouds: Cold diffuse clouds: UV dominatedUV dominated

Cometary ices Cometary ices Oort cloud: Oort cloud: cosmic ray dominatedcosmic ray dominated

Icy solar system bodiesIcy solar system bodies e.g. Mars polar caps: e.g. Mars polar caps: solar wind, solar UVsolar wind, solar UV Galilean satellites: Galilean satellites: magnetospheric ions (dominant) & solar magnetospheric ions (dominant) & solar

wind – wind – OO++, O, O2+2+, O, O3+3+, O, O4+4+, O, O6+6+, , SS++, S, S2+2+, S, S3+3+, S, S4+4+, S, S5+5+, S, S22++, SO, SO22

++, , NaNa++, K, K2+2+, C, C6+6+, H, H22OO++, H, H33OO++, OH, OH++, H, H++, He, He++, H, H22

++ and H and H33++

The ices can be physically characterised by the:The ices can be physically characterised by the: Thickness, temperature & compositionThickness, temperature & composition Energy, flux & type of processing radiationEnergy, flux & type of processing radiation

In our laboratory regime:In our laboratory regime: Ices are already present, i.e. not concerned with ice Ices are already present, i.e. not concerned with ice

accretion / formation accretion / formation thick ice layers (to ignore the effect of the substrate)thick ice layers (to ignore the effect of the substrate) Ion, photon and electron irradiationIon, photon and electron irradiation


To pumping station

Electrical feed-through Rotary feed-

through

Detectors (Spectroscopy):UV-VIS / FTIR spectrometerPMT

Sources (Spectroscopy):UV-VIS / FTIR spectrometerSynchrotron

Liquid Helium / Liquid Nitrogen Cryostat

Resistive heaterRhodium-iron RTD

CaF2 substrateCopper sample mount

Ion gauge

50.15

Liquid nitrogen exhaust

Cryogen inlet via transfer line

Temperature controller

HV (UHV) chamber:HV (UHV) chamber: P~10P~10-7-7-10-10-10-10 mbar mbar

CaFCaF22 substrate for substrate for transmission spectroscopytransmission spectroscopy

120 nm – 10 120 nm – 10 mm Temperature:Temperature:

LN2 / LHe cryostatLN2 / LHe cryostat >30 K>30 K Rh-Fe sensorRh-Fe sensor Resistive coax. HeaterResistive coax. Heater

4 ports4 ports Sample depositionSample deposition SpectroscopySpectroscopy IrradiationIrradiation

Transmission spectra Transmission spectra recorded vs. wavelength / recorded vs. wavelength / frequencyfrequency

Portable ApparatusPortable Apparatus


Sample PreparationSample Preparation

• Ice layers are vapour deposited directly onto a cold substrate.

• The gases are prepared in a reservoir prior to dosing

• Pure gases or mixtures

• Sample thickness is determined from the pressure of gas deposited.

• Ice thickness is calibrated by measuring the absorption through the sample (column densities) or analysing interference fringes

TurboPump

To rotary Feed-through

To RotaryPump for roughing

Liquid sample Gas from

Lecture bottle

UHV

Gas reservoir

Baratron

ON/OFF Valve

PrecisionLeak Valve

ON/OFF valve

Needle valve

Gas regulator

Pirani Gauge

~10m thick CO2 ice (left)

~3 m thick H2O ice (right)


RadiationRadiation SourceSource EnergyEnergy

PhotonPhoton

Hydrogen LampHydrogen Lamp(on-site not yet in operation)(on-site not yet in operation)

Synchrotron RadiationSynchrotron Radiation(Daresbury SRS & (Daresbury SRS & ÅÅrhus ASTRID)rhus ASTRID)

Limited WavelengthsLimited Wavelengths(Lyman-(Lyman- dominated) dominated)

Tuneable: (3-10eV)Tuneable: (3-10eV)(grating monochromator)(grating monochromator)

ElectronElectron Electron Gun Electron Gun (on-site not yet in operation)(on-site not yet in operation)

< 20 eV< 20 eV

Ion:Ion:

singly and singly and multiply chargedmultiply charged

Van de Graff AcceleratorVan de Graff Accelerator (QUB)(QUB)

ECR Ion sourceECR Ion source (QUB)(QUB)

keV – MeVkeV – MeV

Low keVLow keV

Sample IrradiationSample Irradiation

1 hour of irradiation in the lab is equivalent to 1000 years 1 hour of irradiation in the lab is equivalent to 1000 years irradiation in space!irradiation in space!

Once deposited, the samples are irradiated with either photons, ions or Once deposited, the samples are irradiated with either photons, ions or electronselectrons

• The products may be probed at regular intervals by The products may be probed at regular intervals by

spspecectrtrososcocopypy• UV-UV-VVIISS & VUV & VUV : Electronic Structure: Electronic Structure• FTIR FTIR : Vibrational Structure: Vibrational Structure


What are we currently looking at?What are we currently looking at?

Study of HStudy of H22O, COO, CO22 and H and H22O:COO:CO22 ices ices These are two of the most abundant moleculesThese are two of the most abundant molecules Present in all astrophysical environments (grain mantles, Present in all astrophysical environments (grain mantles,

comets, Galilean satellites, Mars & Triton.comets, Galilean satellites, Mars & Triton.

Irradiation with ionsIrradiation with ions 100 keV H100 keV H++

Low energy (1-5 keV) Low energy (1-5 keV) singlysingly charged ions charged ions Low energy (1-5*q keV) Low energy (1-5*q keV) multiplymultiply charged ions charged ions implantation – implantation – reactivereactive ions: ions: CC++ on H on H22O and HO and H++ on CO on CO22

Irradiation with photonsIrradiation with photons Zero order Synchrotron radiationZero order Synchrotron radiation Discrete wavelengths (synchrotron grating monochromator)Discrete wavelengths (synchrotron grating monochromator)

Products we are looking for in HProducts we are looking for in H22O:COO:CO22 ices: ices: Carbonic acid (HCarbonic acid (H22COCO33)) CO, COCO, CO33, H, H22O:COO:CO22 complex, HCO, O complex, HCO, O33(?) and others (?)(?) and others (?)

FTIR spectraFTIR spectra


Irradiation of HIrradiation of H22O:COO:CO22 ice at 90 K with ice at 90 K with100 keV H100 keV H++

H2O

H2OH2O

CO2

13CO2

CO2

H2O:CO2

H2O

H2OH2O

CO2

13CO2

CO2

H2O:CO2

H2CO3

(2850) H2CO3

(2580)

CO(2140)

CO3

(2044)

H2CO3

(1703)

H2CO3

(1488)H2CO3

(1295)

After 1 hour irradiationAfter 1 hour irradiation


H2O

H2OH2O

CO2

13CO2

H2O:CO2

H2O

H2OH2O

CO2

13CO2

H2O:CO2

H2CO3

(2850) H2CO3

(2580)

CO(2140)

H2CO3

(1703)

H2CO3

(1488)H2CO3

(1295)NO CO3!

After 0.5 hour irradiationAfter 0.5 hour irradiation

Irradiation of HIrradiation of H22O:COO:CO22 ice at 50 K with ice at 50 K with5 keV H5 keV H++


Warm-up after Warm-up after HH++ Irradiation Irradiation of Hof H22O:COO:CO22 ice ice

50 K100 K120 K140 K

CO2

H2O

H2O

160 K

CO2

H2OH2O

H2O

CO

Crystalline

H2O

CO2

H2O180 K

CO2

H2OH2O

H2O

CO

200 K

H2O

H2O H2O

CO2

220 K

H2OCO2

Temp:

H2CO3

H2CO3

250 K


HH22COCO33 yield after irradiation with yield after irradiation with

HH++,, HeHe++,, OO++ andand NeNe++ (all at 5 keV)(all at 5 keV)

Yield depends on:Yield depends on: Ion range?Ion range? Reactive, Reactive,

unreactive ion?unreactive ion?

Low or no yield Low or no yield with multiply with multiply charged ions (Ncharged ions (N3+3+, , NN5+5+, N, N6+6+) – ) – not not shown hereshown here::

Lack of secondary Lack of secondary electrons?electrons?

Small penetration Small penetration depth?depth?


The CO profileThe CO profile

The 2152 cmThe 2152 cm-1-1 CO CO feature possible feature possible origin:origin:

formation at formation at different sites in different sites in the ice matrix the ice matrix (substitutional / (substitutional / interstitial)interstitial)

(Sandford et.al. ApJ 329, 498-(Sandford et.al. ApJ 329, 498-510, 1998)510, 1998)

CO diffusion into CO diffusion into unirradiated ice unirradiated ice and interaction and interaction with the dangling with the dangling OH bondsOH bonds

(Palumbo, J Phys Chem A, (Palumbo, J Phys Chem A, 101, 4298-4301, 1997)101, 4298-4301, 1997)

(Sandford et.al. ApJ 329, 498-510, 1998)


0.012

0.017

0.022

0.027

0.032

0.037

0.042

0.047

212021302140215021602170

Wavenumber (cm-1)

ABS

0.012

0.017

0.022

0.027

0.032

0.037

0.042

0.047

212021302140215021602170

0.012

0.017

0.022

0.027

0.032

0.037

0.042

0.047

212021302140215021602170

0.012

0.017

0.022

0.027

0.032

0.037

0.042

0.047

212021302140215021602170

0.012

0.017

0.022

0.027

0.032

0.037

0.042

0.047

212021302140215021602170

CO formation by irradiation of HCO formation by irradiation of H22O:COO:CO22=1 with different =1 with different ions (5*q keV) at 50Kions (5*q keV) at 50K

The 2152 cmThe 2152 cm-1-1 CO CO feature :feature :

Increases with mass Increases with mass of ionof ion

interstitial ?interstitial ?

Increases with Increases with decreasing decreasing penetration depth of penetration depth of ionion

diffusion ?diffusion ? Repeated Repeated

experiment at ~ 100 experiment at ~ 100 K with heavier K with heavier ions.....ions..... No 2152 No 2152 feature!feature!

diffusion ?diffusion ?

(CO partially sublimes >27 (CO partially sublimes >27 K)K)

CO

H+

He+

N3+

O+

Ne+


97.8

97.9

98.0

98.1

98.2

98.3

98.4

98.5

98.6

98.7

98.8

21202125213021352140214521502155216021652170

Wavenmber (cm-1)

%Tra

nsm

issi

on

Irradiation of pure HIrradiation of pure H22O with 2 keV CO with 2 keV C++

Irradiation time 00:00

97.8

97.9

98.0

98.1

98.2

98.3

98.4

98.5

98.6

98.7

98.8

21202125213021352140214521502155216021652170

Wavenmber (cm-1)

%Tra

nsm

issi

on

00:15

97.8

97.9

98.0

98.1

98.2

98.3

98.4

98.5

98.6

98.7

98.8

21202125213021352140214521502155216021652170

Wavenmber (cm-1)

%Tra

nsm

issi

on

00:30

97.8

97.9

98.0

98.1

98.2

98.3

98.4

98.5

98.6

98.7

98.8

21202125213021352140214521502155216021652170

Wavenmber (cm-1)

%Tra

nsm

issi

on

00:45

97.8

97.9

98.0

98.1

98.2

98.3

98.4

98.5

98.6

98.7

98.8

21202125213021352140214521502155216021652170

Wavenmber (cm-1)

%Tra

nsm

issi

on

01:00

97.8

97.9

98.0

98.1

98.2

98.3

98.4

98.5

98.6

98.7

98.8

21202125213021352140214521502155216021652170

Wavenmber (cm-1)

%Tra

nsm

issi

on

01:15

97.8

97.9

98.0

98.1

98.2

98.3

98.4

98.5

98.6

98.7

98.8

21202125213021352140214521502155216021652170

Wavenmber (cm-1)

%Tra

nsm

issi

on

COApolar Component Polar Component

2152 cm-1 feature

01:15


Summary of Results... Summary of Results... More questions...?More questions...?

CO, COCO, CO33 and H and H22COCO33 were seen after irradiation of H were seen after irradiation of H22O:COO:CO22 with 100 keV H with 100 keV H++

But...But...

No HNo H22COCO33 seen with highly charged ions (or signal too weak?) seen with highly charged ions (or signal too weak?) Low penetration depth?Low penetration depth? Lack of secondary electrons?Lack of secondary electrons? PE vs KE effect?PE vs KE effect?

No CONo CO33 seen after irradiation of H seen after irradiation of H22O:COO:CO33 with low (<5*q keV) with low (<5*q keV) energy/multiply charged ions!energy/multiply charged ions!

KE vs PE effect?KE vs PE effect? Nuclear vs electronic stopping?Nuclear vs electronic stopping?

2152 cm2152 cm-1-1 feature of CO was seen in H feature of CO was seen in H22O:COO:CO22 irradiated ice with heavier irradiated ice with heavier ions at T<60 Kions at T<60 K

But...But...

2152 cm2152 cm-1-1 feature was not seen in H feature was not seen in H22O:COO:CO22 irradiated ice with any ion at T > irradiated ice with any ion at T > 90 K90 K Many more...Many more...


To do... To do... Search for Answers!Search for Answers!

Changing the beam...Changing the beam... Singly vs. multiply charged ionsSingly vs. multiply charged ions

kinetic vs. potential effects?kinetic vs. potential effects? Secondary electrons...Secondary electrons...

Different energiesDifferent energies nuclear vs. electronic stopping nuclear vs. electronic stopping

effect of ions (latter dominates effect of ions (latter dominates as energy increases)as energy increases)

Different ions Different ions Effect of ion Effect of ion

mass/momentum/velocitymass/momentum/velocity Reactive / unreactive ionsReactive / unreactive ions Implantation – chemical vs. Implantation – chemical vs.

physical effectsphysical effects Low energy electron irradiationLow energy electron irradiation

Secondary electron effect Secondary electron effect following ion irradiationfollowing ion irradiation

Ion vs. Photon irradiationIon vs. Photon irradiation Systematic comparisonSystematic comparison

Changing the sample...Changing the sample... TemperatureTemperature

Diffusion (e.g. CO)Diffusion (e.g. CO) Activation energyActivation energy Crystalline vs. amorphous iceCrystalline vs. amorphous ice Get down to 10K!!Get down to 10K!!

CompositionComposition Isotopic substitution to identify Isotopic substitution to identify

reaction pathwaysreaction pathways Ratio of componentsRatio of components

StructureStructure PorosityPorosity Crystalline vs. amorphous iceCrystalline vs. amorphous ice

ThicknessThickness Ion / photon penetration depthIon / photon penetration depth ImplantationImplantation


GeneralGeneral SummarySummaryGeneralGeneral SummarySummary More experimental work is needed to fully understand the mechanisms More experimental work is needed to fully understand the mechanisms

involved in synthesis of molecules under astrophysical environments...involved in synthesis of molecules under astrophysical environments...

The design of the new apparatus allows flexibility to perform a wide The design of the new apparatus allows flexibility to perform a wide variety of experiments, using different sources to irradiate samples and variety of experiments, using different sources to irradiate samples and implement a variety of spectroscopic techniques using different implement a variety of spectroscopic techniques using different instruments.instruments. Ion accelerators – Belfast (singly & multiply charged ions)Ion accelerators – Belfast (singly & multiply charged ions) Synchrotron Sources – Synchrotron Sources – ÅÅrhus & Daresbury (irradiation & rhus & Daresbury (irradiation &

spectroscopy... Circular dichroism)spectroscopy... Circular dichroism)

Electron and photon sources Electron and photon sources

These experiments will enable us to better understand the processes These experiments will enable us to better understand the processes behind chemical processing if ices in the ISM and the planets, satellites, behind chemical processing if ices in the ISM and the planets, satellites, comets and meteorites within our solar system.comets and meteorites within our solar system. (The apparatus can also (The apparatus can also be adapted to study atmospheric ices e.g. polar stratospheric clouds)be adapted to study atmospheric ices e.g. polar stratospheric clouds)

A systematic experimental approach is required to identify reaction A systematic experimental approach is required to identify reaction pathways and intermediates whilst pinning down the different variables pathways and intermediates whilst pinning down the different variables (both sample and irradiation parameters).(both sample and irradiation parameters).

Many more experiments to come...Many more experiments to come...


AcknowledgementsAcknowledgements

Nigel MasonNigel Mason

Stephen BrottonStephen BrottonMike DavisMike DavisPhilip HoltomPhilip Holtom

Bob McCulloughBob McCulloughand Ian Williams and Ian Williams (QUB)(QUB)

Roland TrasslRoland Trassl(Geissen University)(Geissen University)

SSøøren Vrønning ren Vrønning HoffmannHoffmann(ASTRID, (ASTRID, Århus)Århus)

Documents

Ion Irradiation of Astrophysical Ice Analogues