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VUV Spectroscopy of VUV Spectroscopy of Astrophysical IcesAstrophysical Ices
Michael DavisMichael Davis
IntroductionIntroduction
Experimental backgroundExperimental background Apparatus and techniquesApparatus and techniques Results and spectraResults and spectra DiscussionDiscussion
BackgroundBackground
Accretion of gas phase atoms and
molecules
A mantle of simple volatile molecules
is formed, processed by
UV/charged pratical irradiation
An outer volatile mantle protects an inner organic mantle from irradiation
Chemical explosions and other processes release molecules into the gas phase
BackgroundBackground
Ion irradiation Ion irradiation caused by Jupiter’s caused by Jupiter’s magnetospheremagnetosphere
Ices exist in bulkIces exist in bulk Higher temperatures Higher temperatures
(~100K) than ISM (~100K) than ISM (~10K)(~10K)
ApparatusApparatus
ApparatusApparatus
Designed to travel to Designed to travel to irradiation sourcesirradiation sources
CaF/MgFCaF/MgF22 substrate substrate
for IR/UV for IR/UV transmissiontransmission
Helium/nitrogen Helium/nitrogen cryogens, achieves cryogens, achieves temperatures <20Ktemperatures <20K
Reaches base Reaches base pressure 10pressure 10-8-8mbarmbar
Ion gauge
Rotary feed-through
Sample mount
Cryogen inlet
ApparatusApparatus
Sample deposition
Irradiation
Detection methods
FT
IR
SO
UR
CE
RF DEUTERIUM DISCHARGE
LAMP (UV)
DE
TE
CT
OR
FTIR Spectroscopy
VUV Spectroscopy
PMTSYNCHROTRON
SOURCE
ELECTRON GUN
ION
SO
UR
CE
SY
NC
HR
OT
RO
N
ExperimentsExperiments
VUV spectroscopy undertaken at:VUV spectroscopy undertaken at: ISA Storage Ring, University of AarhusISA Storage Ring, University of Aarhus SRS, Daresbury LaboratorySRS, Daresbury Laboratory
Most recent beam-times September 2004 Most recent beam-times September 2004 (ISA) and December 2004 (SRS)(ISA) and December 2004 (SRS)
Looking at simple ices (NHLooking at simple ices (NH33, CO, CO, CO, CO22) )
and mixtures with waterand mixtures with water Depositions at different speeds and Depositions at different speeds and
temperaturestemperatures
ExperimentsExperiments
Why use VUV spectroscopy?Why use VUV spectroscopy? Complements FTIR studiesComplements FTIR studies Highlight differences between gas and solid Highlight differences between gas and solid
phase VUV dataphase VUV data Knowing electronic transitions allows to Knowing electronic transitions allows to
know the effects of irradiation by UV know the effects of irradiation by UV discharge lamp discharge lamp
ExperimentsExperiments
Presenting NHPresenting NH33 and NH and NH33/H/H22O resultsO results
Depositing at 25K, 75K, 85K and 95KDepositing at 25K, 75K, 85K and 95K Annealing up to 120KAnnealing up to 120K Depositing ~0.2µm in <2 minutes and Depositing ~0.2µm in <2 minutes and
~30 minutes~30 minutes Mixtures at 9:1, 1:1 and 1:3 ratiosMixtures at 9:1, 1:1 and 1:3 ratios
Deposition speedDeposition speed
In ammonia, no In ammonia, no difference in curve difference in curve featuresfeatures
Absorbance is Absorbance is increasedincreased
Other molecules Other molecules show drastic show drastic changeschanges
0
0.5
1.0
1.5
2.0
2.5
140 160 180 200 220
NH3 deposited at 20K in 93s
NH3 deposited at 20K in 1760s
Wavelength (nm)
Ab
sorb
an
ce
Temperature EffectsTemperature Effects
Annealing from Annealing from 20K to >75K shifts 20K to >75K shifts the main peak and the main peak and adds another adds another featurefeature
Depositing at 95K Depositing at 95K has a similar has a similar effect, but more effect, but more pronouncedpronounced 0
1
2
3
140 160 180 200
NH3 dep. at 20K
NH3 ann. at 110K
NH3 dep. at 95K
Wavelength (nm)
Ab
sorb
an
ce
194nm
Temperature EffectsTemperature Effects
Depositing at Depositing at ~75K-85K causes ~75K-85K causes major changesmajor changes
New features New features seen, existing seen, existing features modifiedfeatures modified
0
1
2
3
140 160 180 200
NH3 dep. at 20K
NH3 dep. at 72.5K
NH3 dep. at 87K
NH3 dep. at 95K
Wavelength (nm)
Ab
sorb
an
ce
194nm
Temperature EffectsTemperature Effects
Some features Some features enhanced or enhanced or decreaseddecreased
No major changes No major changes to curve shapeto curve shape
Completely Completely different result different result than annealing the than annealing the 20K sample20K sample 0
0.5
1.0
1.5
2.0
2.5
140 160 180 200
NH3 dep. at 72.5K
NH3 ann. at 118K
Wavelength (nm)
Ab
sorb
an
ce
NHNH33:H:H22O MixturesO Mixtures
Adding small Adding small amounts of water amounts of water to the ammonia to the ammonia does not change does not change the spectra the spectra significantlysignificantly
No water features No water features visiblevisible
0
0.5
1.0
1.5
2.0
2.5
140 160 180 200
NH3 dep. at 20K
NH3:H
2O 10:1 dep. at 28K
NH3 dep. at 72.5K
NH3:H
2O 9:1 dep. at 72K
Wavelength (nm)
Ab
sorb
an
ce
NHNH33:H:H22O MixturesO Mixtures
Additional HAdditional H22O O
suppresses the suppresses the crystal structurecrystal structure
Some HSome H22O remains O remains
after NHafter NH33 has been has been
desorbeddesorbed No significant No significant
annealing effectsannealing effects0
1
2
3
140 160 180 200
NH3 dep. at 72.5K
NH3:H
2O 1:1 dep. at 72K
NH3:H
2O 1:3 dep. at 77K
NH3:H
2O 1:3 ann. at 150K
H2O dep.at 25K
Wavelength (nm)
Ab
sorb
an
ce
SummarySummary
Outline of experimental techniques and Outline of experimental techniques and apparatusapparatus
Deposition speed has little effect in NHDeposition speed has little effect in NH33
Deposition temperature has a major Deposition temperature has a major effect in NHeffect in NH33
Annealing has some effect on spectraAnnealing has some effect on spectra Sample is not strongly affected by water Sample is not strongly affected by water
“impurities”“impurities”
AcknowledgementsAcknowledgements
Prof. Nigel MasonProf. Nigel Mason Dr Anita DawesDr Anita Dawes Dr Robin MukerjiDr Robin Mukerji Philip HoltomPhilip Holtom Bhalamurugan SivaramanBhalamurugan Sivaraman Sarah WebbSarah Webb David Shaw (SRS)David Shaw (SRS) The Open UniversityThe Open University EPSRCEPSRC PPARCPPARC
