1 / 45

Cheuk-Yiu Ng Department of Chemistry University of California, Davis

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

pmary
Download Presentation

Cheuk-Yiu Ng Department of Chemistry University of California, Davis

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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. Neutral Photodissociation processes in the VUV range were labeled as “dark reactions” • 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: • Synchrotron VUV: Resolution = 1cm-1 and intensity = 109 - 1010 photons/s • VUV laser by 4-wave mixing: Resolution = 0.1 cm-1 and intensity = 1012-1014 photons/pulse

  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 Gas Cell  Y MgF2 Bi-Convex Lens The surface of Slit Without using defraction grating: Achievable tunable VUV Intensities upto : 1012-1014/pulse Images and simulation were done by optical software CODE V

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

  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, N2, and CO2etc.

  7. CO is the second most abundant molecular species after H2 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(3P) + O(1D) C(1D) + O(3P) C(3P) + O(3P) hv 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).

  8. Solar VUV Irradiance in the range shorter than 200 nm Lyman β Irradiance (photons/s/cm3) 1012 1011 1010 109 108 0 50 100 150 200 Wavelength (nm) Relevant to COSS: 91.17-111.78 nm (11.09-13.60 eV)

  9. Experimental plan for VUV photodissociation-pump and VUV photoionization-probe CO(X1) C(3P) + O(3P) E = 11.09 eV  C(1D) + O(3P) E = 12.37 eV  C(3P) + O(1D) E = 13.08 eV By tuning ω2 in the range of 400-900 nm with ω1 fix at the nonlinear medium (Kr or Xe): • The difference-frequency (2ω1-ω2) and sum-frequency (2ω1+ω2) 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

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

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

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

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

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

  15. PFI-PI and PIE bands of O(3P0:3P1:3P2) formed by photodissociation of SO2 at 193 and 212.5 nm I(O+) (arb. Units) n=34 SO2 + h(193.3 and 212.5 nm) → SO(v) + O(3P2)

  16. Total kinetic energy release spectrum for SO2 photodissociation at 193 and 212.5 nm obtained Rydberg tagging of O(3P2)

  17. C(3P0,1,2) Fine Structure Distribution by VUV-UV (1+1’) state-selective photoionization Ionization Continuum UV or VIS 2s22p4s (3P2) 2s22p4s (3P1) 2s22p4s (3P0) VUV 3P2 3P1 3P0

  18. C(3P0,1,2) Fine Structure Distribution VUV-UV (1 + 1’) detection State-selective VUV-(1+1’) photoionization

  19. C(3P2) + O(1D) -------- (BR-III)*(F2) C(3P1) + O(1D) -------- (BR-II)*(F1) C(3P) + O(1D) C(3P0) + O(1D) -------- (BR-I)*(F0) CO + VUV C(3P2) + O(3P) -------- [1-(BR-III)]*(F2) C(3P1) + O(3P) -------- [1-(BR-II)]*(F1) C(3P) + O(3P) C(3P0) + O(3P) -------- [1-(BR-I)]*(F0) BR-I = [C(3P0) + O(1D)] / { [C(3P0) + O(3P)] + [C(3P0) + O(1D)] } BR-II = [C(3P1) + O(1D)] / { [C(3P1) + O(3P)] + [C(3P1) + O(1D)] } BR-III = [C(3P2) + O(1D)] / { [C(3P2) + O(3P)] + [C(3P2) + O(1D)] } F0 = [C(3P0)] / {[C(3P0)] + [C(3P1)] + [C(3P2)]} F1 = [C(3P1)] / {[C(3P0)] + [C(3P1)] + [C(3P2)]} F2 = [C(3P2)] / {[C(3P0)] + [C(3P1)] + [C(3P2)]}

  20. Correlated fine structure distribution of the channel C(3P0,1,2) + O(1D2) [O(3PJ)]

  21. VUV Photodissociation of CO2 CO2 Early earth’s atmosphere Carrier of O2 Mars Venus VUV-VUV-VMI-PI apparatus

  22. Photoproduct channels for VUV photodissociation of CO2 CO2 + hv→ CO(X 1Σ+) + O(3P) hv > 5.45 eV(1) CO2 + hv→ CO(X 1Σ+) + O(1D) hv > 7.42 eV (2) CO2 + hv→ CO(X 1Σ+) + O(1S) hv > 9.64 eV (3) CO2 + hv→ CO(a 3Π) + O(3P) hv > 11.46 eV (4) CO2 + hv→ CO(a 3Π) + O(1D) hv > 13.43 eV (5) CO2 + hv→ CO(a′ 3Σ+) + O(3P) hv > 12.31 eV (6) CO2 + hv→ CO(d 3∆) + O(3P) hv > 12.97 eV (7) CO2 + hv→ CO(e 3Σ-) + O(3P) hv > 13.35 eV (8) CO2 + hv→ CO(A1Π) + O(3P) hv > 13.48 eV (9) CO2 + hv→ CO(I 1Σ-) + O(3P) hv > 13.45 eV (10) CO2 + hv→ CO(D 1∆) + O(3P) hv > 13.56 eV (11)

  23. Comparison of absorption and O(3P2) photofragment spectra of CO2

  24. The detection of O atoms VUV-Visible photoionization VUV autoionization 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).

  25. Decoding the photochemistry of CO2 hv

  26. The fine structure branching ratio of CO(a3Π) + O(3PJ) and CO(X1Σ+) + O(3PJ) channelsat CO2 4s Rydberg state

  27. The VMI-PI images and corresponding KER spectra for the CO(X1Σ+) + O(1S) channel recorded at (a)12.125 eV, (b) 12.145 eV, and (c)12.150 eV.

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

  29. The VMI-PI images and corresponding KER spectra for the CO(X1Σ+) + O(1D) channel recorded at (a)12.125 eV, (b) 12.145 eV, and (c)12.150 eV.

  30. CO2 photodissociation: angular distribution of the CO(ν) + O(3P2,1,0) [O(1D), and O(1S)] photofragment channels CO (1Σ+) + O(3P2) CO (1Σ+) + O (1D) CO (1Σ+) + O (1S)

  31. Calculated Excited CO2 potential energy surfaces

  32. Singlet potential energy surfaces calculated at MRCI level of theory • CO(X1Σ+) + O (1S) channel: exclusively via 4 1Aʹ PES • CO(X1Σ+) + O (1D) channel: via 3 1Aʹ PES from conical • intersection between 3 1Aʹ and 4 1Aʹ PES at ~3.5 bohr

  33. Comparison of CO2 absorption spectrum with the C(3P2) and O(1S) PHOFEX spectra L. Archer et al.Journal of Quantitative Spectroscopy and Radiative Transfer117, 88 (2013) VUV2-Vis photoionization [2s22p3d (3D°3)] VUV2 autoionization [2s22p3(2P°)3s (1P°1)] C is an exit channel in CO2 photodissociation

  34. C(3P2) photofragment excitation spectrum Roaming Pathway 2 O C C O O O C … Energy (eV) O OC O C(3P) + O2(X3Σg-) O C O O O (11.44 eV) 1Σ+ C O O C Singlet Pathway 1 1A1 (7.13 eV) (6.03 eV) hv hv O C D. Y. Hwang and A. M. Mebel, Chemical Physics 256, 169 (2000) S. Y. Grebenshchikov, The Journal of Chemical Physics 138, 224106 (2013) CO2(X1Σg+) O

  35. C+ ion TOF spectra TOF spectrum at the CO2 (3p1Πu103) Rydberg state CO2 + hν(VUV1) → C(3PJ) + O2(X3Σg-) C(3PJ) + hν(VUV2) → C+ + e- The C+ ion signal relates to both the photodissociation (VUV1) and photoionization (VUV2) laser radiations

  36. C(3P2) velocity-map ion images

  37. Threshold of the C(3P) + O2(X3Σg-) channel

  38. VUV photodissociation of N2 Photodissociation of N2: N2 + hv1 → N(4S) + N(4S) hv ≥ 9.759 eV N2 + hv1 → N(4S) + N(2D) hv ≥ 12.139 eV N2 + hv1 → N(4S) + N(2P) hv≥ 13.339 eV N2 + hv1 → N(2D) + N(2D) hv ≥ 14.529 eV VUV1 VUV2 N(4S) + hv2 → N+ + e- or N(2D) + hv2 → N+ + e-

  39. Branching ratios for the spin-forbidden N(4S) + N(2D) and N(4S) + N(2D) channels and the spin-allowed N(2D) + N(2D) channel from N2 valence and Rydberg states with 1Πusymmetry. The upward arrows indicate the thresholds of the N(4S) + N(2P) and N(2D) + N(2D) channels

  40. Branching ratios for the spin-forbidden N(4S) + N(2D) and N(4S) + N(2D) channels and the spin-allowed N(2D) + N(2D) channel from N2 valence and Rydberg states with 1Σu+ symmetry. The upward blue arrows indicate the threshold of the N(4S) + N(2P) and N(2D) + N(2D) channels.

  41. Greetings from Ng Group 2013 Thank you:

  42. Greetings from Ng Group 2013 Thank you:

More Related