Statetostate photodissociation studies by VUV photodissociationpump and VUVphotoionizationprobe

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

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: source • Synchrotron VUV: Resolution = 1 cm-1 and intensity = 109 - 1010 photons/s • VUV laser by 4 -wave mixing: Resolution = 0. 1 cm-1 and intensity = 1012 -1014 photons/pulse

Vacuum Ultraviolet Laser Tunable range (7. 0 -19. 0 e. V) Four-wave sum and differencefrequency mixings in rare gases or metal vapors: high efficiency

The Simulation of VUV Laser Separation from Fundamentals by Convex Lens Rcell (um) RSlit (um) Y(mm) ( ) Visible ( 2) 57. 8 443 -17. 9 3. 4 UV ( 1) 17. 3 512 -19. 6 3. 7 VUV (2 1 - 2) 16. 6 119 -25. 0 4. 7 12 cm Gas Cell 30 cm 8 mm Y Mg. F 2 Bi-Convex Lens Without using defraction grating: Achievable tunable VUV Intensities upto : 1012 -1014/pulse The surface of Slit Images and simulation were done by optical software CODE V

VUV laser velocity-mapped ion- and electronimaging appartatus Tunable VUV laser radiation Molecular beam Imaging MCP Photodissociation laser 193 nm Imaging TOF chamber

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.

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 Catom 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) C(3 P) + O(3 P) 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).

Irradiance (photons/s/cm 3) Solar VUV Irradiance in the range shorter than 200 nm Lyman β 1012 1011 1010 109 108 0 50 100 150 200 Wavelength (nm) Relevant to COSS: 91. 17 -111. 78 nm (11. 09 -13. 60 e. V)

Experimental plan for VUV photodissociation-pump and VUV photoionization-probe CO(X 1 ) C(3 P) + O(3 P) C(1 D) + O(3 P) C(3 P) + O(1 D) E = 11. 09 e. V E = 12. 37 e. V E = 13. 08 e. V 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 e. V. • Difference-frequencies for photodissociation excitation • Sum frequencies for photoionization sampling

Development of the VUV laser velocity-mapped imaging photoion (VMI-PI) apparatus CO + VUV C(3 P) + O(3 P) C(1 D) + O(3 P) C(3 P) + O(1 D) 11. 05 e. V 12. 31 e. V 13. 02 e. V 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!

Branching Ratio Measurements (a) (b): R(0) line of (4 pσ)1Σ+(v'=3) at 109484. 7 cm-1 (c) (d): R(0) line of (4 sσ)1Σ+(v'=4) at 109452. 5 cm-1

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).

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

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

I(O+) (arb. Units) 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 n=34 SO 2 + h (193. 3 and 212. 5 nm) → SO(v) + O(3 P 2)

Total kinetic energy release spectrum for SO 2 photodissociation at 193 and 212. 5 nm obtained Rydberg tagging of O(3 P 2)

C(3 P 0, 1, 2) Fine Structure Distribution by VUV-UV (1+1’) state-selective photoionization Ionization Continuum UV or VIS 2 s 22 p 4 s (3 P 2) 2 s 22 p 4 s (3 P 1) 2 s 22 p 4 s (3 P 0) VUV 3 P 2 3 P 1 3 P 0

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

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 (4 sσ)1Σ+(v = 4), (4 pσ)1Σ+(v = 3), and (4 pπ)1Π(v = 3) states Predissociative CO states Fine structure distribution in % via common state: C*[2 s 22 p 4 s (3 P 1)] 3 P 0 3 P 1 3 P via Common state : C*[2 s 22 p 3 d (3 D 1)] 2 3 P 0 3 P 1 3 P 2 (4 sσ)1Σ+(v=4) 69 ± 2 10 ± 2 21 ± 2 67 ± 4 8± 3 25 ± 3 (4 pσ)1Σ+(v=3) 54 ± 2 22 ± 2 51 ± 4 23± 3 26 ± 2 (4 pπ)1Π(v=3) 28 ± 4 40 ± 4 32 ± 5 30 ± 9 33± 12 37 ± 2

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

BR-III (4 sσ)1Σ+(v=4) 0. 62± 0. 03 0. 09± 0. 01 0. 08± 0. 01 (4 pσ)1Σ+(v=3) 0. 37± 0. 02 0. 03± 0. 02 0. 12± 0. 01 (4 pπ)1Π(v=3) 0. 20± 0. 01 0. 59± 0. 03 0. 13± 0. 01 Correlated fine structure distribution of the channel C(3 P 0, 1, 2) + O(1 D 2) [O(3 PJ)] 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 PJ) C(3 P 1)+O(3 PJ) C(3 P 0)+O(3 PJ) (4 sσ)1Σ+(v=4) 1. 7± 0. 3 0. 9± 0. 2 42. 4± 3. 0 19. 3± 2. 0 9. 1± 1. 9 26. 6± 2. 3 (4 pσ)1Σ+(v=3) 2. 7± 0. 4 0. 7± 0. 4 19. 7± 1. 6 19. 3± 1. 9 23. 3± 2. 3 34. 3± 2. 2 (4 pπ)1Π(v=3) 4. 3± 1. 1 23. 4± 3. 4 5. 5± 0. 9 27. 7± 4. 8 16. 6± 2. 7 22. 5± 3. 3

VUV Photodissociation of CO 2 Mars Early Venus earth’s atmosphere Carrier of O 2 VUV-VMI-PI apparatus

Photoproduct channels for VUV photodissociation of CO 2 + hv → CO(X 1Σ+) + O(3 P) CO 2 + hv → CO(X 1Σ+) + O(1 D) CO 2 + hv → CO(X 1Σ+) + O(1 S) CO 2 + hv → CO(a 3Π) + O(3 P) CO 2 + hv → CO(a 3Π) + O(1 D) CO 2 + hv → CO(a′ 3Σ+) + O(3 P) CO 2 + hv → CO(d 3∆) + O(3 P) CO 2 + hv → CO(e 3Σ-) + O(3 P) CO 2 + hv → CO(A 1Π) + O(3 P) CO 2 + hv → CO(I 1Σ-) + O(3 P) CO 2 + hv → CO(D 1∆) + O(3 P) hv > 5. 45 e. V hv > 7. 42 e. V hv > 9. 64 e. V hv > 11. 46 e. V hv > 13. 43 e. V hv > 12. 31 e. V hv > 12. 97 e. V hv > 13. 35 e. V hv > 13. 48 e. V hv > 13. 45 e. V hv > 13. 56 e. V (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11)

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

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).

Decoding the photochemistry of CO 2 hv

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

The VMI-PI images and corresponding KER spectra for the CO(X 1Σ+) + O(1 S) channel recorded at (a)12. 125 e. V, (b) 12. 145 e. V, and (c)12. 150 e. V.

Vibrational population Plot of β parameters as a function of v

The VMI-PI images and corresponding KER spectra for the CO(X 1Σ+) + O(1 D) channel recorded at (a)12. 125 e. V, (b) 12. 145 e. V, and (c)12. 150 e. V.

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 (1Σ+) + O(3 P 2) CO (1Σ+) + O (1 D) CO (1Σ+) + O (1 S)

Calculated Excited CO 2 potential energy surfaces

Singlet potential energy surfaces calculated at MRCI level of theory • CO(X 1Σ+) + O (1 S) channel: exclusively via 4 1 Aʹ PES • CO(X 1Σ+) + O (1 D) channel: via 3 1 Aʹ PES from conical intersection between 3 1 Aʹ and 4 1 Aʹ PES at ~3. 5 bohr

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 -Vis photoionization [2 s 22 p 3 d (3 D° 3)] VUV 2 autoionization [2 s 22 p 3(2 P°)3 s (1 P° 1)] C is an exit channel in CO 2 photodissociation

C(3 P 2) photofragment excitation spectrum hv O Energy (e. V) C Roaming Pathway 2 C C O OC … O O C(3 P) + O 2(X 3Σg-) O O C 1 A hv (11. 44 e. V) (7. 13 e. V) Singlet Pathway 1 (6. 03 e. V) O C O O C 1Σ+ 1 C O CO 2(X 1Σg+) D. Y. Hwang and A. M. Mebel, Chemical Physics 256, 169 (2000) S. Y. Grebenshchikov, The Journal of Chemical Physics 138, 224106 (2013)

C+ ion TOF spectra TOF spectrum at the CO 2 (3 p 1Πu 103) Rydberg state CO 2 + hν(VUV 1) → C(3 PJ) + O 2(X 3Σg-) C(3 PJ) + hν(VUV 2) → C+ + e- The C+ ion signal relates to both the photodissociation (VUV 1) and photoionization (VUV 2) laser radiations

C(3 P 2) velocity-map ion images

Threshold of the C(3 P) + O 2(X 3Σg-) channel

VUV photodissociation of N 2 Photodissociation of N 2: N 2 + hv 1 → N(4 S) + N(4 S) N 2 + hv 1 → N(4 S) + N(2 D) N 2 + hv 1 → N(4 S) + N(2 P) N 2 + hv 1 → N(2 D) + N(2 D) VUV 1 hv ≥ 9. 759 e. V hv ≥ 12. 139 e. V hv≥ 13. 339 e. V hv ≥ 14. 529 e. V VUV 2 N(4 S) + hv 2 → N+ + e- or N(2 D) + hv 2 → N+ + e-

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 1Πu symmetry. The upward arrows indicate thresholds of the N(4 S) + N(2 P) and N(2 D) + N(2 D) channels

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 1Σu+ symmetry. The upward blue arrows indicate threshold of the N(4 S) + N(2 P) and N(2 D) + N(2 D) channels.

Greetings from Ng Group 2013 Thank you:

Greetings from Ng Group 2013 Thank you: