1. Near-Infrared Spectroscopy of Interstellar and Planetary Ice Analogs
Amanda M. Cook
Dr. Perry A. Gerakines
Research Funded by a grant from the NSF REU program

2. Where are ices detected?
Interstellar Clouds
CO: Triton, Pluto, Comets
NH3: Miranda, Charon
CH4: Triton, Pluto, Kuiper Belt Objects, Comets
Background is Neptune’s satellite, Triton
Miranda: moon of uranus
Charon: pluto’s moon
Kuiper belt: a disk-like cloud of comets that lies beyond Neptune’s orbit, out to about 120 AU (pluto lies at ~40 AU)…Oort cloud ~100,000 AU
HOW ARE ICES DETECTED?

3. Combined Near-IR and Mid-IR Spectra of N2+CH4
Spectroscopy
Bending Modes
Stretching Modes
Resonance
Combined Near-IR and Mid-IR Spectra of N2+CH4
10000
8000
6000
4000
2000
0.0
0.5
1.0
1.5
Absorbance
Wavenumber (cm-1) O H
Asymmetric vs. Symmetric stretch
For example, the bending mode of water is on the right
The stretching mode is on the left
This spectrum shows that just like any other kind of vibration, these molecular vibrations also have resonance, which means they vibrate in the same mode, at different frequencies. The fundamental frequencies are generally found in the mid IR, while the harmonic frequencies show much smaller features and are found in the near-IR
OUR GOAL: to correlate near-IR features in astronomical ice analogs with those in the mid-IR
HOW DO WE DO THIS IN THE LAB?

4. Experimental Set-up Gas Bulb UV lamp Infrared Beam from Spectrometer
Turbo-pump
Helium Cooling
System
Gas Bulb
UV lamp
Infrared Beam from Spectrometer
Sample Chamber
Average pressure: between 5x10-7 and 5x10-6 torr …..atmospheric pressure is 760 torr
Average Temp: K
Build ice slowly to expose to UV (ice ends up being ~ microns in thickness)
SO HERE’S THE DATA WE CAME UP WITH, USING THESE METHODS…

5. NH3+CO Photolysis Products
The important things to notice here are the differences in the two spectra
1330 and 1338: formamide– HCONH2
1505 and 1700: H2CO—formaldehyde
2160: OCN- cyanate ion
POINT OUT NIR REGION

6. A Closer Look…
Now we’re going to take a closer look at the this tiny peak

7. NH3+CO Photolysis Product
A comparison of 4 different spectra. The bottom is an unphotolyzed sample; the top three are in order according to length of photolyzation
At ~4710 wavenumbers
Wavenumber: a measure of frequency; the reciprocal of wavelength.
The wavelength of infrared is slightly longer than that of visible light.
Frequency of vibration, as shown by the previous slide
There is a high possibility that the 4710 feature could be a harmonic vibration of the CO2 stretching feature at However, we did a pure CO2 deposit, and this feature did not show up at all. Nonetheless, the possibility remains.,

8. Identifying the Feature
Pure Ethylene
Pure CO2 Deposit
NOT CO2….
Probably not Ethylene, either because we have none of the other features of ethylene in our spectrum
Quirico and Schmitt (1997)

9. Triton Spectrum
The wavelength is shown here in microns. The wavelength of our feature in microns is about 2.1 microns.
Notice the peak to the left of where I have marked. The author has identified it as CO2.
It’s possible that we may have created this unidentified feature in our own ice sample. Even though we cannot identify our feature with much certainty, at this point, it still helps to know the the feature was produced with a certain mixture of NH3+CO, and not with any methane (CH4) in the mixture. This may give us clues fro further investigation of Triton’s chemical composition.
NOW WE ALSO DID ANOTHER MIXTURE : N2+CH4
Cruikshank et al. (1993)

10. N2+CH4 Photolysis Products
Propane (red) C3H8: 743, 2885, 2978
Ethane (blue) C2H6: 820, 2235, 2942
Shows that there were photolysis products….we DID make something, it just didn’t show up in the near ir

11. Triton, molecule, serine (amino acid), dna, life (maybe even intelligent life)
If nothing else, we can understand more clearly how WE evolved in the universe.
THANK YOU