methanol photodissociation and its role in the complex chemistry of the interstellar...

Methanol Photodissociation and its Role in the

Complex Chemistry of the Interstellar MediumJacob C. Laas†, Mary L. Radhuber†, Robin T. Garrod,‡ and Susanna L. Widicus Weaver†

†Department of Chemistry, Emory University, Atlanta, GA 30322‡Department of Astronomy, Cornell University, Ithaca, NY 14853

Final Abundances for High-Mass Hot Core

Chemical Abundances During Hot Core Warm-Up

Objectives• Accurately determine methanol photolysis

branching ratios using molecular spectroscopy

• Use astrochemical models to study effects of

photolysis branching ratios on complex

interstellar chemistry

Motivation• Methanol photolysis branching ratios are

largely unmeasured, but are thought to play a

major role in complex interstellar chemistry:

CH3OH CH2OH + H

CH3O + H

CH3 + OH

CH2O + H2

CH2 + H2O

HCOH + H2

hν

Highly reactive radicals!

HCOglycolaldehyde

methyl formate

acetaldehyde

Methanol Photolysis• Methanol photolysis is efficient at many

wavelengths from 120-200 nm; branching

ratios change with wavelength

• THz spectroscopy is being used for

quantitative monitoring of gas-phase

photolysis products

Astrochemical Modeling• Ice composition was set to match observations and earlier model1

• Branching ratios of three primary methanol photolysis product

channels were adjusted

• Two-stage physical model involving collapse and gradual warm-

up was used

• Molecular abundances were monitored as a function of time

References1 Robin T. Garrod, Susanna L. Widicus Weaver, & Eric Herbst 2008, Ap. J., 682, 283-302.

AcknowledgementsEric Herbst, Thomas Orlando, & Michael Heaven

Results & Future Work• Photolysis branching ratios influence relative abundances of

structural isomers and formation of complex organic molecules

• Branching ratios with CH3 at 90% gave best match to Sgr

• Quantitative gas-phase measurements of branching ratios are

needed to guide future models

• Wavelength dependence of photolysis should also be determined

and incorporated into models

• Future collaboration with Orlando group at GA Tech planned for

condensed-phase measurements