International Symposium on Molecular Spectroscopy, 2017 Direct measurement of OD+CO branching kinetics using time-resolved frequency comb spectroscopy Bryce J Bjork JILA and University of Colorado at Boulder International Symposium on Molecular Spectroscopy, 2017

A key reaction in atmospheric and combustion chemistry The OH+CO Reaction A key reaction in atmospheric and combustion chemistry Strong pressure and anomalous temperature dependencies OH+CO OH…CO TS1 trans-HOCO cis-HOCO TS2 TS3 H-CO2 TS5 H+CO2 -120 -80 -40 40 Energy (kJ/mol) TS4 Reaction Progress kT = 2.5 kJ/mol at 300 K Bjork, Science (2016) and Nguyen et al. Phys. Chem Lett, 3, 1549 (2012)

A key reaction in atmospheric and combustion chemistry The OH+CO Reaction A key reaction in atmospheric and combustion chemistry Strong pressure and anomalous temperature dependencies OH+CO OH…CO TS1 trans-HOCO cis-HOCO TS2 TS3 H-CO2 TS5 H+CO2 -120 -80 -40 40 Energy (kJ/mol) TS4 Reaction Progress kT = 2.5 kJ/mol at 300 K Bjork, Science (2016) and Nguyen et al. Phys. Chem Lett, 3, 1549 (2012)

Imagine you had a tool to see all of these species in real time… The OH+CO Reaction Imagine you had a tool to see all of these species in real time… OH+CO OH…CO TS1 trans-HOCO cis-HOCO TS2 TS3 H-CO2 TS5 H+CO2 -120 -80 -40 40 Energy (kJ/mol) TS4 Reaction Progress kT = 2.5 kJ/mol at 300 K

The Optical Frequency Comb Laser Pulse Time Frequency

The Optical Frequency Comb Laser Pulse Time Frequency

(1) (2) Our tool Mid-IR Frequency Comb Source (3-5 mm) Mid-IR Camera Time (log scale) Wavenumber grating (1) (2) VIPA etalon

(1) (2) (2) Our tool Mid-IR Frequency Comb Source (3-5 mm) Optical Enhancement Cavity Mid-IR Camera Time (log scale) Wavenumber grating (1) (2) (2) VIPA etalon

(1) (2) (3) (2) Our tool Mid-IR Frequency Comb Source (3-5 mm) Optical Enhancement Cavity Spatially Dispersive VIPA Spectrometer (3) Mid-IR Camera Time (log scale) Wavenumber grating (1) (2) (2) VIPA etalon

+ + + Reaction Scheme (( )) 266 nm O(1D) O2 O3 D OD O(1D) D2 OD CO D (( )) D CO2 [M] T = 300 K, Ptotal ≈ 100 Torr

trans-DOCO TS3 40 TS2 TS1 OH+CO OH…CO Energy (kJ/mol) TS5 -40 H-CO2 trans-HOCO cis-HOCO TS2 TS3 H-CO2 TS5 H+CO2 -120 -80 -40 40 Energy (kJ/mol) TS4 Reaction Progress kT = 2.5 kJ/mol at 300 K

trans-DOCO P Q R Data trans-DOCO OD

trans-DOCO

cis-DOCO TS3 40 TS2 TS1 OH+CO OH…CO Energy (kJ/mol) TS5 -40 H-CO2 TS4 trans-HOCO cis-HOCO TS2 TS3 H-CO2 TS5 H+CO2 -120 -80 -40 40 Energy (kJ/mol) TS4 Reaction Progress kT = 2.5 kJ/mol at 300 K

cis-DOCO

D+CO2 TS3 40 TS2 TS1 OH+CO OH…CO Energy (kJ/mol) TS5 -40 H-CO2 TS4 -80 trans-HOCO cis-HOCO TS2 TS3 H-CO2 TS5 H+CO2 -120 -80 -40 40 Energy (kJ/mol) TS4 Reaction Progress kT = 2.5 kJ/mol at 300 K

D+CO2

Reactants and Products trans-DOCO cis-DOCO CO2

Concentrations vs. Time 1b OD + CO DOCO* D + CO2 M 1a DOCO

D+CO2 OD + CO DOCO* D + CO2 DOCO M 1a 1b CO2 Formation OD Decay

Mass Balance Our measurement Golden et al. (1998) OD + CO DOCO* D + CO2 DOCO M 1a 1b Our measurement Golden et al. (1998) Paraskevopoulos & Irwin (1982)

Isomerization

Isomerization

Simple Isomerization A B Initially, we start with [A]/[B] = 1

Isomerization (+5) (+2.5) (+0) (-2.5) (-5) [CO] formation equilibrium / steady-state

Isomerization Rate formation isomerization loss cis → trans trans → cis

Summary TS3 40 TS2 TS1 OH+CO OH…CO Energy (kJ/mol) TS5 -40 H-CO2 TS4 trans-HOCO cis-HOCO TS2 TS3 H-CO2 TS5 H+CO2 -120 -80 -40 40 Energy (kJ/mol) TS4 Reaction Progress

Acknowledgements Mid-IR Team Thinh Bui Oliver Heckl Kana Iwakuni Bryce Bjork (now at Vienna) Bryan Changala Collaborators: Mitchio Okumura (Caltech) Dave Patterson (Harvard) John Doyle (Harvard) Garrett Cole (CMS) Ben Spaun Jun Ye

Thank you for your attention!