DETERMINATION OF METHANOL PHOTOLYSIS BRANCHING RATIOS VIA ROTATIONAL

DETERMINATION OF METHANOL PHOTOLYSIS BRANCHING RATIOS VIA ROTATIONAL SPECTROSCOPY Carson Powers, Morgan N. Mc. Cabe, Susanna L. Widicus Weaver Department of Chemistry, Emory University Wednesday, June 21, 2017

Methanol Photolysis in the Interstellar Medium (ISM) h ν Radicals are mobile on grain surfaces at T > 20 K and can combine with other radicals. CH 3 OH hν CH 2 OH + H CH 3 O + H CH 3 + OH HCO H 2 O, CH 3 OH, NH 3 , H 2 CO Ice mantle glycolaldehyde methyl formate CH 3 CO Garrod R. T. , Widicus Weaver S. L. , & Herbst E. Astrophys. J. , 682, 283 -304, 2008. CH 3 acetone

Previous Studies of Methanol Photolysis Branching Ratios Hagege et al. (1968) (gas phase, mass spec) ~75% Öberg et al. (2009) (condensed phase, IR) ~73% ~15% ~12% ~20% ~0% Öberg et al. A&A, 504, 891 -913, 2009. Hagege J. , Roberge P. C. , Vermeil C. Trans. Faraday Soc. , 64, 3288 -3299, 1968.

Experimental Setup Pulsed Valve with Fused Silica Capillary Tube Beam Block Excimer Laser Cylindrical Focusing Lens Oscilloscope Microwave Synthesizer (250 k. Hz-50 GHz) Multipass Optical System Millimeter/Submillimeter Frequency Multiplier (x 3 -x 27) Detector

Multipass Optical Path

Parent Methanol Reference Lines

Rotation Diagram for Parent Methanol T = 12 ± 5 K Nmethanol = (1. 19 ± 0. 03)× 1017 cm-2

Laser Photolysis + Methanol Depletion

Formaldehyde Photolysis Product T = 19 K N/Nmethanol = (3. 7 ± 0. 4)× 10 -5

Methanol Dissociation 140 Energy (kcal/mol) 120 100 80 60 40 20 0 Hays B. M. , Wehres N. , Alligood De. Prince B. A. , Roy A. L. M. , Laas J. C. , & Widicus Weaver S. L. Chem. Phys. Lett. , 630, 18 -26, 2015. Lyman alpha = 235. 19 kcal/mol

Methoxy Photolysis Product Scaling x 100 Scaling x 10 T = 3. 7 K N/Nmethanol = (6 ± 2)× 10 -4

Hydroxymethyl Photolysis Product T = 0. 6 K N/Nmethanol = (8. 1 ± 3)× 10 -4 Based on frequencies reported by Bermudez, Bailleux and Cernicharo, 2016, A&A, 598, A 9. Caveats: -- No line strength information included -- Our fit of the reported lines does not converge

Methanol Photolysis Branching Ratios Hagege et al. Trans. Faraday Soc. , 64, 1968 Öberg et al. A&A 504, 2009

Conclusions and Future Work Determine optimal laser position on tube Try different Ar/CH 3 OH ratios Collect more hydroxymethyl lines, refine fit Measure other branching ratios for COMs Try other laser wavelengths, compare branching ratio changes

Acknowledgements Luyao Zou, AJ Mesko, Kevin Roenitz Undergraduates: (on project) Samuel Zinga; (off project) Elena Jordanov, Lindsay Rhoades, Houston Smith Past Group Members: Brian Hays and Jake Laas NASA Emerging Worlds Award NNX 15 AH 74 G

Boltzmann Diagram Analysis Variables Values h Planck constant c Speed of light A Einstein A coefficient Upper State degeneracy k Boltzmann constant Frequency (MHz) Number density Rotational Partition Function Upper State Energy Rotational Temperature