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The Liberation of CO from Photoprocessed Methanol Ice

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Presentation on theme: "The Liberation of CO from Photoprocessed Methanol Ice"— Presentation transcript:

1 The Liberation of CO from Photoprocessed Methanol Ice
Houston Smith, AJ Mesko, and Susanna L. Widicus Weaver Department of Chemistry, Emory University Stefanie Milam NASA GSFC

2 Interstellar Medium Interstellar medium (ISM) is abundant in chemical species in star-forming regions Thousands of lines visible in a chemically rich source Sarah M. Fortman et al. 2012, J. Mol. Spectrosc., Volume 280, Pages 11-20

3 Schematic of a Star-forming region
T (gas) = K T (dust) ~90 K ~60 K ~45 K ~20 K CO2 CO N2 O2 ice complex organics H2O, CH3OH, NH3 CH3OH ice H2S SiO CH3CN CO2 ice trapped CO UV H2O ice Hot Core ~1016 cm ~5x1017 cm

4 Relevant Chemical Pathways in the ISM
H2O + hn OH + H H2 + O CH3OH + hn CH3 + OH CH3O + H CH2OH + H H2CO + hn HCO + H hn H2O, CO, CH3OH, H2CO Ice mantle HCO + CH2OH HOCH2CHO (glycolaldehyde) HCO + CH3O CH3OCHO (methyl formate) HCO + OH HCOOH (formic acid) HCO + CH3 CH3CHO (acetaldehyde) CH3 + CH3O CH3OCH3 (dimethyl ether) CH3 + CH2OH CH3CH2OH (ethanol) CH2OH + CH2OH HOCH2CH2OH (ethylene glycol) Garrod, Widicus Weaver, & Herbst, ApJ 682, 2008

5 Millimeter/Submillimeter Spectroscopy
Above a Processed Ice Sample Stage Detector Multiplier Chain Frequency Synthesizer Lock-In Amplifier UV Lamp Sample Line Cryostat Computer

6 Experimental Setup

7 Proof of Concept Experiments
Detection of desorbed water from a pure ice using a temperature programmed desorption experiment (TPD) Detection of photodesorbed water

8 TPD of Pure Water Ice (10,1)  (11,0)

9 Water Photodesorption
10,1  11,0

10 Relevant Chemical Pathways in the ISM
H2O + hn OH + H H2 + O CH3OH + hn CH3 + OH CH3O + H CH2OH + H H2CO + hn HCO + H hn H2O, CO, CH3OH, H2CO Ice mantle HCO + CH2OH HOCH2CHO (glycolaldehyde) HCO + CH3O CH3OCHO (methyl formate) HCO + OH HCOOH (formic acid) HCO + CH3 CH3CHO (acetaldehyde) CH3 + CH3O CH3OCH3 (dimethyl ether) CH3 + CH2OH CH3CH2OH (ethanol) CH2OH + CH2OH HOCH2CH2OH (ethylene glycol) Garrod, Widicus Weaver, & Herbst, ApJ 682, 2008

11 Methanol Photolysis There was no direct methanol or methanol products, CH3O, or H2CO, photodesorption Methanol was shown to more readily photofragment than photodesorb from methanol ice Bertin et al. 2016, ApJ Lett., 817, L12

12 Photo and Thermal Processing of Methanol Ice
Two different experiments were conducted to determine the temperature at which CO is liberated from methanol ice The first experiment had simultaneous photoprocessing and thermal processing The second experiment had photoprocessing for a period of time and then thermal processing

13 Simultaneous Photo and Thermal Processing of Methanol Ice
J=5  4 J =5  4

14 Methanol TPD from Photoprocessed Methanol Ice
32,0  21,0

15 TPD of CO from a Photoprocessed Methanol Ice
J= 5  4

16 Comparison to Previous Studies
CO Thermal Desorption from Photoprocessed Methanol Ice 100 K 120 K 140 K 160 K 200 K 180 K 220 K Pure CO Ice Thermal Desorption1 Pure Methanol Ice Thermal Desorption2 CO Desorption from Simultaneous Processing of Methanol Ice Pure Methanol Ice Thermal Desorption 1. Oberg et al. A&A 449, (2006) 2. Martin-Domenech et al. A&A 1406 (2014)

17 Future Work Verification of CO results
Calibration of the PID loop temperature controller has been done since these measurements were performed Ice thickness measurements Use TPD of pure H2O, CH3OH, and CO ices as a calibration tool to corroborate literature values Addition of FTIR to monitor ice directly Increasing sensitivity by using multipass optics or cavity enhanced detection in Fall 2017 Determine the temperature at which other photofragments of methanol such as CH2OH, CH3O, and H2CO are liberated from photoprocessed methanol ice.

18 Acknowledgements The Widicus Weaver Group: Carson Powers, Kevin Roenitz, Samuel Zinga Former group members: Luyao Zou, AJ Mesko, Lindsay Rhoades, Elena Jordanov, Morgan McCabe, Brian Hays, Nadine Wehres, Jacob Laas, Anthony Chirillo, Mateo Correa, Jim Sanders, Trevor Cross, Althea Roy, Bridget Alligood DePrince, Mary Radhuber, Danna Qasim, Blithe Rocher, Shiya Wang, Jessica Walsh O’Sullivan, Brandon Carroll, Anne Carroll, Jay Kroll, Brett McGuire, Sophie Lang, Thomas Anderson NASA GSFC SIF Program NASA Award NNX16AE49A NASA EW Grant NNX15AH74G Michael Heaven, Emory Eric Herbst and Robin Garrod, UVA Thomas Orlando, GA Tech Reggie Hudson and Perry Gerakines, NASA GSFC

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