1. State-to-state photodissociation studies by VUV-photodissociation-pump and VUV-photoionization-probe method Cheuk-Yiu Ng Department of Chemistry University of California, Davis Photo dissociation in Astrochemistry Leiden Observatory Workshop (Feb. 3-5, 2015)

2. Most neutral photodissociation processes have not been explored because of the lack of intense tunable VUV light sources. Can we now take on this challenge? Improvement in VUV laser source Improvement in VUV laser source: Synchrotron VUV: Resolution = 1cm -1 and intensity = 10 9 - 10 10 photons/s VUV laser by 4-wave mixing: Resolution = 0.1 cm -1 and intensity = 10 12 -10 14 photons/pulse Neutral Photodissociation processes in the VUV range were labeled as “dark reactions”

3. Vacuum Ultraviolet Laser Tunable range (7.0-19.0 eV) Four-wave sum and difference- frequency mixings in rare gases or metal vapors: high efficiency

4. The Simulation of VUV Laser Separation from Fundamentals by Convex Lens 12cm 30cm 8mm MgF 2 Bi-Convex Lens The surface of Slit Gas Cell R cell (um)R Slit (um)Y(mm) ()() Visible (  2 ) 57.8443-17.93.4 UV (  1 ) 17.3512-19.63.7 VUV (2  1 -  2 ) 16.6119-25.04.7 Y  Images and simulation were done by optical software CODE V Without using defraction grating: Achievable tunable VUV Intensities upto : 10 12 -10 14 /pulse

5. VUV laser velocity-mapped ion- and electron- imaging appartatus Tunable VUV laser radiation Molecular beam Imaging TOF chamber Photodissociation laser 193 nm Imaging MCP

6. State-to-state photodissociation Study State-to-state photodissociation studies by VUV laser photodissociation pump VUV laser photoionization probe Goals: To apply on photodissociation Atmospheric gases CO, N 2, and CO 2 etc.

7. CO is the second most abundant molecular species after H 2 in the interstellar medium. Thus, VUV photodissociation study of CO is very important to understand the properties of the interstellar medium, planet formation, and C- atom and O-atom isotope fractionation. CO photodissociation in the VUV region is still largely unknown. C( 3 P) + O( 1 D) C( 1 D) + O( 3 P) M. Eidelsberg, F. Launay, K. Ito, T. Matsui, P. C. Hinnen, E. Reinhold, W. Ubachs, and K. P. Huber, J. Chem. Phys., 121 (1), 292 (2004). C( 3 P) + O( 3 P) hvhv

8. 0 50 100 150 200 Wavelength (nm) Irradiance (photons/s/cm 3 ) 10 12 10 1110 10 9 10 8 Solar VUV Irradiance in the range shorter than 200 nm Relevant to COSS: 91.17-111.78 nm (11.09-13.60 eV) Lyman β

9. Experimental plan for VUV photodissociation-pump and VUV photoionization-probe By tuning ω 2 in the range of 400-900 nm with ω 1 fix at the nonlinear medium (Kr or Xe): The difference-frequency (2ω 1 -ω 2 ) and sum-frequency (2ω 1 +ω 2 ) can be generated in the respective ranges of 6.9-11.5 and 11.3-16.0 eV. Difference-frequencies for photodissociation excitation Sum frequencies for photoionization sampling CO(X 1  )  C( 3 P) + O( 3 P)  E = 11.09 eV  C( 1 D) + O( 3 P)  E = 12.37 eV  C( 3 P) + O( 1 D)  E = 13.08 eV

10. Development of the VUV laser velocity-mapped imaging photoion (VMI-PI) apparatus CO + VUV  C( 3 P) + O( 3 P) 11.05 eV C( 1 D) + O( 3 P) 12.31 eV C( 3 P) + O( 1 D) 13.02 eV C( 3 P) + VUV  C + + e - C( 1 D) + VUV  C + + e - We found that photodissociation and photoionization can be accomplished with the same laser pulse!

11. (a) (b): R(0) line of (4pσ) 1 Σ + (v'=3) at 109484.7 cm -1 (c) (d): R(0) line of (4sσ) 1 Σ + (v'=4) at 109452.5 cm -1 Branching Ratio Measurements

12. R. Visser, E. F. van Dishoeck, and J. H. Black, Astron. Astrophys. 503 (2), 323 (2009). Branching Ratio measurements : 25 identified predissociative vibronic bands Above dissociation energy of CO

13. The branching ratio into the spin-forbidden channel strongly depends on the vibronic state of CO excited by the VUV photon. Dissociation into the channel C( 1 D) + O( 3 P) Branching Ratio Measurements for CO

14. Dissociation into the channel C( 1 D)+O( 3 P) Strong rotational dependence Rotational dependence

16. PFI-PI and PIE bands of O( 3 P 0 : 3 P 1 : 3 P 2 ) formed by photodissociation of SO 2 at 193 and 212.5 nm I(O + ) (arb. Units) SO 2 + h  (193.3 and 212.5 nm) → SO(v) + O( 3 P 2 ) n=34

17. Total kinetic energy release spectrum for SO2 photodissociation Total kinetic energy release spectrum for SO2 photodissociation at 193 and 212.5 nm obtained Rydberg tagging of O( 3 P 2 )

18. 3P03P0 3P13P1 3P23P2 2s 2 2p4s ( 3 P 0 ) 2s 2 2p4s ( 3 P 1 ) 2s 2 2p4s ( 3 P 2 ) VUV Ionization Continuum C( 3 P 0,1,2 ) Fine Structure Distribution by VUV-UV (1+1’) state-selective photoionization UV or VIS

19. State-selective VUV-(1+1’) photoionization C( 3 P 0,1,2 ) Fine Structure Distribution VUV-UV (1 + 1’) detection

20. Fine structure distributions (in %) for C( 3 P 0, 3 P 1, and 3 P 2 ) Fine structure distributions (in %) for C( 3 P 0, 3 P 1, and 3 P 2 ) formed by VUV photodissociation of CO excited in the N = 1 rotational levels of the (4sσ) 1 Σ + (v = 4), (4pσ) 1 Σ + (v = 3), and (4pπ) 1 Π(v = 3) states Predissociative CO states Fine structure distribution in % via common state: C*[2s 2 2p4s ( 3 P 1 )] via Common state : C*[2s 2 2p3d ( 3 D 1 )] 3P03P0 3P13P1 3P23P2 3P03P0 3P13P1 3P23P2 (4sσ)1Σ+(v=4)69 ± 210 ± 221 ± 267 ± 48±325 ± 3 (4pσ)1Σ+(v=3)54 ± 224 ± 2 22 ± 251 ± 423±326 ± 2 (4pπ)1Π(v=3)28 ± 440 ± 432 ± 530 ± 933±1237 ± 2

21. CO + VUV C( 3 P) + O( 1 D) C( 3 P) + O( 3 P) C( 3 P 0 ) + O( 1 D) -------- (BR-I)*(F0) C( 3 P 1 ) + O( 1 D) -------- (BR-II)*(F1) C( 3 P 2 ) + O( 1 D) -------- (BR-III)*(F2) C( 3 P 0 ) + O( 3 P) -------- [1-(BR-I)]*(F0) C( 3 P 1 ) + O( 3 P) -------- [1-(BR-II)]*(F1) C( 3 P 2 ) + O( 3 P) -------- [1-(BR-III)]*(F2) BR-I = [C( 3 P 0 ) + O( 1 D)] / { [C( 3 P 0 ) + O( 3 P)] + [C( 3 P 0 ) + O( 1 D)] } BR-II = [C( 3 P 1 ) + O( 1 D)] / { [C( 3 P 1 ) + O( 3 P)] + [C( 3 P 1 ) + O( 1 D)] } BR-III = [C( 3 P 2 ) + O( 1 D)] / { [C( 3 P 2 ) + O( 3 P)] + [C( 3 P 2 ) + O( 1 D)] } F0 = [C( 3 P 0 )] / {[C( 3 P 0 )] + [C( 3 P 1 )] + [C( 3 P 2 )]} F1 = [C( 3 P 1 )] / {[C( 3 P 0 )] + [C( 3 P 1 )] + [C( 3 P 2 )]} F2 = [C( 3 P 2 )] / {[C( 3 P 0 )] + [C( 3 P 1 )] + [C( 3 P 2 )]}

22. BR-IBR-IIBR-III (4sσ) 1 Σ + (v=4) 0.62±0.03 0.09±0.01 0.08±0.01 (4pσ) 1 Σ + (v=3)0.37±0.020.03±0.020.12±0.01 (4pπ) 1 Π(v=3)0.20±0.010.59±0.030.13±0.01 C( 3 P 2 )+O( 1 D)C( 3 P 1 )+O( 1 D)C( 3 P 0 )+O( 1 D)C( 3 P 2 )+O( 3 P J )C( 3 P 1 )+O( 3 P J )C( 3 P 0 )+O( 3 P J ) (4sσ) 1 Σ + (v=4)1.7±0.30.9±0.242.4±3.019.3±2.09.1±1.926.6±2.3 (4pσ) 1 Σ + (v=3)2.7±0.40.7±0.419.7±1.619.3±1.923.3±2.334.3±2.2 (4pπ) 1 Π(v=3)4.3±1.123.4±3.45.5±0.927.7±4.816.6±2.722.5±3.3 Correlated fine structure distribution of the channel C( 3 P 0,1,2 ) + O( 1 D 2 ) [O( 3 P J )]

23. CO 2 MarsVenus Early earth’s atmosphere VUV Photodissociation of CO 2 Carrier of O 2 VUV-VUV-VMI-PI apparatus

24. CO 2 + hv → CO(X 1 Σ + ) + O( 3 P)hv > 5.45 eV(1) CO 2 + hv → CO(X 1 Σ + ) + O( 1 D)hv > 7.42 eV(2) CO 2 + hv → CO(X 1 Σ + ) + O( 1 S)hv > 9.64 eV(3) CO 2 + hv → CO(a 3 Π) + O( 3 P)hv > 11.46 eV(4) CO 2 + hv → CO(a 3 Π) + O( 1 D)hv > 13.43 eV(5) CO 2 + hv → CO(a′ 3 Σ + ) + O( 3 P)hv > 12.31 eV(6) CO 2 + hv → CO(d 3 ∆) + O( 3 P)hv > 12.97 eV(7) CO 2 + hv → CO(e 3 Σ - ) + O( 3 P)hv > 13.35 eV(8) CO 2 + hv → CO(A 1 Π) + O( 3 P) hv > 13.48 eV(9) CO 2 + hv → CO(I 1 Σ - ) + O( 3 P) hv > 13.45 eV(10) CO 2 + hv → CO(D 1 ∆) + O( 3 P) hv > 13.56 eV(11) Photoproduct channels for VUV photodissociation of CO 2

25. Comparison of absorption and O( 3 P 2 ) photofragment spectra of CO 2

26. The detection of O atoms Z. Lu, Y. C. Chang, H. Gao, Y. Benitez, Y. Song, C. Y. Ng and W. M. Jackson, Journal of Chemical Physics, In press (2014). VUV-Visible photoionization VUV autoionization

27. Decoding the photochemistry of CO 2 hv

28. The fine structure branching ratio of CO(a 3 Π) + O( 3 P J ) and CO(X 1 Σ + ) + O( 3 P J ) channels at CO 2 4s Rydberg state

29. The VMI-PI images and corresponding KER spectra for the CO(X 1 Σ + ) + O( 1 S) channel recorded at (a)12.125 eV, (b) 12.145 eV, and (c)12.150 eV.

30. Vibrational population Plot of β parameters as a function of v

31. The VMI-PI images and corresponding KER spectra for the CO(X 1 Σ + ) + O( 1 D) channel recorded at (a)12.125 eV, (b) 12.145 eV, and (c)12.150 eV.

32. CO 2 photodissociation: angular distribution of the CO(ν) + O( 3 P 2,1,0 ) [O( 1 D), and O( 1 S)] photofragment channels CO ( 1 Σ + ) + O ( 1 S) CO ( 1 Σ + ) + O ( 1 D) CO ( 1 Σ + ) + O( 3 P 2 )

33. Calculated Excited CO2 potential energy surfaces

34. Singlet potential energy surfaces calculated at MRCI level of theory CO(X 1 Σ + ) + O ( 1 S) channel: exclusively via 4 1 A ʹ PES CO(X 1 Σ + ) + O ( 1 D) channel: via 3 1 A ʹ PES from conical intersection between 3 1 A ʹ and 4 1 A ʹ PES at ~3.5 bohr

35. Comparison of CO 2 absorption spectrum with the C( 3 P 2 ) and O( 1 S) PHOFEX spectra L. Archer et al. Journal of Quantitative Spectroscopy and Radiative Transfer 117, 88 (2013) VUV 2 autoionization [2s 2 2p 3 ( 2 P°)3s ( 1 P° 1 )] VUV 2 -Vis photoionization [2s 2 2p3d ( 3 D° 3 )] C is an exit channel in CO 2 photodissociation

36. C( 3 P) + O 2 (X 3 Σ g - ) CO 2 (X 1 Σ g + ) hv 1A1 1A1 1Σ+1Σ+ (11.44 eV) (6.03 eV) (7.13 eV) hv Singlet Pathway 1 C( 3 P 2 ) photofragment excitation spectrum Roaming Pathway 2 Energy (eV) D. Y. Hwang and A. M. Mebel, Chemical Physics 256, 169 (2000) S. Y. Grebenshchikov, The Journal of Chemical Physics 138, 224106 (2013) O C O C O O C O O C O O O C O C O OC O … C O O

37. C + ion TOF spectra TOF spectrum at the CO 2 (3p 1 Π u 1 0 3 ) Rydberg state The C + ion signal relates to both the photodissociation (VUV 1 ) and photoionization (VUV 2 ) laser radiations CO 2 + hν(VUV 1 ) → C( 3 P J ) + O 2 (X 3 Σ g - ) C( 3 P J ) + hν(VUV 2 ) → C + + e -

38. C( 3 P 2 ) velocity-map ion images

39. Threshold of the C( 3 P) + O 2 (X 3 Σ g - ) channel

40. VUV 2 VUV 1 VUV photodissociation of N 2 Photodissociation of N 2 : N 2 + hv 1 → N( 4 S) + N( 4 S) hv ≥ 9.759 eV N 2 + hv 1 → N( 4 S) + N( 2 D) hv ≥ 12.139 eV N 2 + hv 1 → N( 4 S) + N( 2 P) hv≥ 13.339 eV N 2 + hv 1 → N( 2 D) + N( 2 D) hv ≥ 14.529 eV N( 4 S) + hv 2 → N + + e - or N( 2 D) + hv 2 → N + + e -

41. Branching ratios for the spin-forbidden N( 4 S) + N( 2 D) and N( 4 S) + N( 2 D) channels and the spin-allowed N( 2 D) + N( 2 D) channel from N 2 valence and Rydberg states with 1 Π u symmetry. The upward arrows indicate the thresholds of the N( 4 S) + N( 2 P) and N( 2 D) + N( 2 D) channels

42. Branching ratios for the spin-forbidden N( 4 S) + N( 2 D) and N( 4 S) + N( 2 D) channels and the spin-allowed N( 2 D) + N( 2 D) channel from N 2 valence and Rydberg states with 1 Σ u + symmetry. The upward blue arrows indicate the threshold of the N( 4 S) + N( 2 P) and N( 2 D) + N( 2 D) channels.

44. Thank you: Greetings from Ng Group 2013

45. Thank you: Greetings from Ng Group 2013