1. Current team Mikhail Ryazanov Dr. Chirantha Rodrigo Overtone-induced dissociation and isomerization of the hydroxymethyl (CH 2 OH) radical First team: Lin Feng Dr. Jie Wei, Boris Karpichev Support: US Department of Energy CH 2 OH + 4 OH  CH 2 O + H OSU 66 th MSS, June 2011 Theory collaborators Dr. Eugene Kamarchik, Prof. Anna Krylov, Prof. Joel Bowman

2. CH 2 OH radical: dissociation on the ground state 11,600 ~ 15,000 cm -1 ~ 14,000 ~3,000 0 Wavenumbers  10 3 cm -1 2 1 (X 2 A″)CH 2 OH CH 3 O H + CH 2 O (X) ~ ~ ~ 1 2 3 4 5 O-H IR 10,484 13,600 ~16,000 7,158 3,675

3. Previous work on the hydroxymethyl radical Characterized ionization and excited Rydberg states, including conical intersections Studied excited state photochemistry Demonstrated the breaking of the weak O-H bond in CH 2 OH following IR overtone excitation Today: direct dissociation dynamics vs. isomerization CH 2 OH IE = 7.56 eV Feng, Wei, and Reisler, J. Phys. Chem. A, 108, 7903 (2004). Wei, Karpichev, and Reisler, J. Chem. Phys. 125 (3): 34303-34303 (2006).

4. Challenges – OH-stretch is the reaction coordinate for direct OH bond cleavage: How high can we go? – Isomerization vs. direct O-H fission; relative barrier heights – OH-overtone pumping is always hard: CH 3 OH, NH 2 OH, HOOH, etc. (Crim, Rizzo, Perry, etc.); – Radical is a minor species and hard to make – CH 2 OH has low-lying electronic states: Will we get substantial vibrationally mediated dissociation?

5. Detection of CH 2 OH via 1+1 REMPI 10 30 40 0 Wavenumbers  10 3 cm -1 (X 2 A″) ~ CH 2 OH CH 3 O H + CH 2 O (X) ~  14,000 11,000 15,000 cm -1 H + CH 2 O (X) ~ CsCs 3p z ( 2 A") 3p x 3s = 26,000 cm -1 Barrier heights: Radom, Schaeffer; Harding, Klippenstein; Temps; Walch…

6. OH stretch vibration: 1-3 OH 3 OH ; 10484 cm -1 ; linewidth = 0.4 cm -1 2 OH ; 7158 cm -1 ; linewidth = 0.8 cm- 1 1 OH ; 3678 cm -1 ; linewidth = 0.4 cm -1 T = 10-13 K

7. Simulation of 2 nd overtone spectrum: a/b–type transition Wei, Karpichev, Reisler, J. Chem. Phys.(2006) No H atom detected 3 OH ; Laser linewidth: 0.1 cm -1 Observed linewidth = 0.4 cm -1

8. New imaging arrangement: Slice imaging of H photofragments Lenses in field free region control VMI conditions and image size 5 ns FWHM pulser allows slicing of H fragment Design based on: A. Suits, K. Liu

9. Br Br* 3685 cm -1

10. 5ns X10 improvement in resolution and sensitivity

11. CH 2 OH H-photofragment yield spectrum in the region of 4 OH Accidental resonance between 4 OH and 3 OH + 1 asymCH [3 OH + 1 asymCH ]* 731.75 nm 13662 cm -1 [4 OH ]* 735 nm 13602 cm -1 Methanol overtone spectrum shows a similar accidental resonance between 5 OH and 4 OH + 1 asymCH. [Rizzo, Perry, Boyarkin]

12. Ground Excited A /cm –1 6.516.0 B /cm –1 1.01 C /cm –1 0.88 90% : 10% : 0% (a:b:c) T: 13 K Linewidths: Laser: 0.1 cm -1 Lorenzian width (FWHM) Strong band: ~ 1.6 cm –1 Weak band: ~ 0.6 cm –1

13. bright state dark states molecular eigenstates spectrum Coupling between a zeroth-order bright state and a dark state

14. H product Ground Excited A /cm –1 3.783.56 B /cm –1 0.840.83 C /cm –1 0.690.73 80% : 20% : 0% (a:b:c) T: 13K D product (small) D signal is is very small 4 OH =13621 cm -1 No other bands observed Lorenzian Linewidths: Both bands: ~ 1.6 cm –1 H and D products from CD 2 OH

15. From maximum KER : D 0 = 10,166 ± 70 cm -1 Compared to calculated D 0 = 10,188 cm -1 (Marenich and Boggs) Vibrational labels of CH 2 O co-fragment are marked. Excited levels = 8%. Rotational temperature of CH 2 O co-fragment: ~ 140 K CH 2 OH: Slice image of H-photofragments from 4 OH peak

16. CH 2 OH + h → H + CH 2 O, = 13662 cm  1 KER of H-photofragments from 3 OH + 1 asymCH peak Vibrational labels of CH 2 O co-fragment are marked. Excited levels = 13%.

17. CD 2 OH: Monitoring H + CD 2 O h = 13621 cm  1 0.04

18. CH 2 OH CD 2 OH Monitoring H 0.04 Formaldehyde cofragment: No CH stretch Ratio of CO str/CHH(D) bends is larger in CD 2 OH

19. Higher rotational and CHD vibrational excitation; No CO stretch CD 2 OH: Monitoring D + CHDO h = 13621 cm  1

20. Summary The OH overtone spectrum of CH(D) 2 OH has been characterized in the 4 OH region. Mixed levels (most likely involving levels 4 OH and 3 OH + 1 asymCH ) are seen in CH 2 OH but not in CD 2 OH. Dissociation, probably by tunneling through the O—H barrier, has been demonstrated. The observation of formaldehyde levels with skeletal CH(D)excitation appears to be associated with isomerization, whereas C=O stretch excitation accompanies O-H bond fission. Isomerization yield is < 10%. It appears to be the result of statistical IVR due to weak high-order resonance couplings. Electronic structure and dynamical calculations are in progress in collaborative work with Dr. Eugene Kamarchik, Joel Bowman (Emory) and Anna Krylov (USC).

21. 10 0 Wavenumbers  10 3 cm -1 H + CH 2 O (X) ~ ~ Calculated Geometries; CCSD(T)/aug-cc-pVTZ Dr. Eugene Kamarchik

22. 355nm Photolyticaly initiated reaction Cl 2  2Cl Cl + CH 3 OH  CH 2 OH + HCl k 1 = 3.7x10 13 (cm 3.mole -1.s -1 ) Radical production CH 2 OH + Cl  CH 2 O + HCl k 2 = 4x10 14 (cm 3.mole -1.s -1 ) ….. CH 3 OH/Cl 2 /He CH 2 OH 355nm

23. CH 2 OH diagnostics: 3p z REMPI or H-photofragment spectrum 0 nl m π co * 3p z (2 2 A”) 1 2 A” C-O Stretch ( 6 ) Progression 0 1 6060 2 6060 C-O

24. Detection schemes for IR spectroscopy Double Resonance CH 2 OH (X 2 A") CH 2 OH + 3p z Probe Pump n OH Scheme 2 Or: Look directly at H atom when the radical dissociates

25. Birge-Sponer plot OH stretchA B, Anharmonicity CH 3 OH 376986.1 CH 2 OH 376691.4 NH 2 OH 374390.6 HOOH 370190.5 potential Anharmonic oscillator /  = A – B   Dissociation barrier > 4ν 1 H-atom generated via tunneling

26. Tunneling: Eckart Potential Linewidth of 1.3 cm -1 corresponds to a tunneling probability of 0.2%; Imaginary frequency= 1712 cm -1 (Larry Harding) Dissociation barrier height of 15,200 cm -1 Theoretical estimation: 14000 – 16000 cm -1 CH 2 OH 9557 cm -1 13598 cm -1 ? 1712 cm -1 CH 2 O + H

27. Next goal: Excite above barrier to dissociation 11,000 16,000cm -1 14,000 ~2,000 0 Wavenumbers  10 3 cm -1 2 1 (X 2 A″)CH 2 OH CH 3 O H + CH 2 O (X) ~ ~ ~ 1 2 3 4 5 O-H IR 11,000 14,600 18,000 7,158 3,675

29. 735 nm 732 nm mode descr. freq. rel. pop. (fit) - ground 0 1 1 1 C-H sym. 2783 - - 2 C=O 1746 0.0203 0.0292 3 CH2 bend 1500 0.0187 0.0293 4* CH2 wag 1167 0.0291 0.0561 5 C-H asym. 2843 - - 6* CH2 rock 1249 0.0166 0.0348 % excited (fit) 7.8 13 % excited (int.) 7.7 12.8 T_rot (fit), K 139 158

30. bright state dark states molecular eigenstates spectrum Coupling between a zeroth-order bright state and a bath of dark states

31. Exciting the 3rd overtone, 4 1 : Monitoring H photofragments from CH 2 OH and CD 2 OH CH 2 OH and CD 2 OH have the same linewidth: 1.3 cm -1 Could not detect deuterium from CD 2 OH Isomerization is at best a minor channel.