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NO-He collisions: First fully state-selected differential

NO-He collisions: First fully state-selected differential cross sections obtained with ion imaging. A.Gijsbertsen , H. Linnartz, J. Klos a , F.J. Aoiz a , E.A. Wade b , D.W. Chandler b and S. Stolte. Department of Physical Chemistry, De Boelelaan 1083, 1081 HV Amsterdam.

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NO-He collisions: First fully state-selected differential

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  1. NO-He collisions: First fully state-selected differential cross sections obtained with ion imaging A.Gijsbertsen, H. Linnartz, J. Klosa, F.J. Aoiza, E.A. Wadeb, D.W. Chandlerb and S. Stolte Department of Physical Chemistry, De Boelelaan 1083, 1081 HV Amsterdam vrije Universiteit amsterdam aDepartamento de Quimica Fisica, Facultad de Quimica,Universidad Complutense, 28040 Madrid, SpainbCombustion Research Facility, Sandia National Laboratories, Livermore, California 94550

  2. Outline • Introduction • Ion imaging • NO-He experiments • Differential cross sections • Conclusions and outlook

  3. Introduction oriented 21/2 NO ( j = ½,  = -1) + R  21/2 NO ( j’,’,’ ) + R With R = Ar, He, D2,...

  4. Introduction NO-Ar, Etr  500 cm-1 Sif NO-He, Etr  500 cm-1 Sif

  5. Introduction • Fluorescence measurements provide only total collision cross sections, we also want to measure differential cross sections to: • Get a better insight on the origin of the “steric effect”. • Test He-NO PESs. • Focus on effect of parity breaking and conservation on the differential cross section.

  6. Introduction Differential cross section He-NO (Sandia) j’=7.5 Th. Ex. Westley et al., J. Chem. Phys. 114, 2669 (2001)

  7. Introduction • Improvements to the experimental setup: • Ion imaging detection (differential cross sections) • More powerful excimer pumped dye laser (to do 1+1’ REMPI, 226 + 308 nm)

  8. 226 nm, 1 mJ 308 nm, 5 mJ He Hexapole NO source chamber NO collision chamber He source dye laser XeCl excimer laser Experimental setup Hexapole state selected NO collides with He at Ecoll  500 cm-1: Crossed 1+1’ REMPI detection excitation  226 nm ionization  308 nm NO (j=½, =½, =-1)  NO ( j’, ’, ’ )

  9. + - + + - + - + + - Ion imaging Ion imaging: Measure a velocity distribution for every rotational state of the NO molecules after collision. MCP + Phosphor screen + CCD camera

  10. velocity mapping

  11. velocity mapping

  12. velocity mapping

  13. velocity mapping

  14. velocity mapping The velocity distribution is recorded with a CCD camera. Ion images show the angular dependence of the inelastic collision cross sections of scattered NO (j’, ’, ’) molecules.

  15. vNO vHe Experiments 200 To test our setup, some 2% NO was seeded in the He beam. The NO beam consists of 16 % NO in Ar. This image reflects the velocity distributions for both our pulsed beams. 300 250 250 300 200 150 350 100 400 50 450 150 200 250 300 350

  16. vNO vHe Some parameters Voltages: Vrepellor= 730 VVextractor = 500 V Sensitivity: S = 7.7 m/s/pixel NO beam velocity: vNO = 590 +/- 25 m/s He beam velocity: vHe= 1760 +/- 50 m/s Images are: - 80 x 80 pixels - averaged over 2000 laser shots (@ 10 Hz) Forward scattering ( = 0): Backward scattering ( = ):

  17. Experiments Parity conserving: p’ = p = - 1 j’ = 1.5 j’ = 2.5 j’ = 3.5 j’ = 4.5 j’ = 5.5 j’ = 6.5 * * j’ = 7.5 j’ = 8.5 j’ = 9.5 j’ = 10.5 j’ = 11.5 j’ = 12.5 *Marked images are from Q-branch transitions that are more sensitive to rotational alignment and show more asymmetry. These images were omitted for the extraction of the DCS.

  18. Experimentally obtained NO-He differential cross sections are compared to recent Hibridon CC calculations using Vsum and Vdif on a RCCSD(T) PES (Klos et al., J. Chem. Phys. 112, 2195 (2000)) Experimentally obtained dcs’s are normalized on the (theoretical) total cross section.

  19. Experiments Parity conserving: p’ = p = - 1

  20. Experiments Parity breaking: p’ = - p = 1 j’ = 1.5 j’ = 2.5 j’ = 3.5 j’ = 4.5 j’ = 5.5 j’ = 6.5 * * * * * j’ = 7.5 j’ = 8.5 j’ = 9.5 j’ = 10.5 j’ = 11.5 j’ = 12.5

  21. Experiments Parity breaking: p’ = - p = 1

  22. NO-He P12 (’=3/2,’=1) j’ = 1.5 j’ = 2..5 j’ = 3.5 j’ = 4.5 j’ = 5.5 j’ = 6.5 j’ = 7.5 j’ = 8.5 j’ = 9.5 j’ = 10.5 j’ = 11.5 j’ = 12.5 15-03-2004

  23. Conclusions and Outlook • Ion imaging setup works very well. • The use of a hexapole makes crossed beam ion imaging experiments more sensitive and easier instead of more difficult. • Our experimental results overall agree with quantum calculations. They show slightly more forward scattering. • A propensity rule for the DCS is seen experimentally. • Measurements of orientation dependence of the DCSs will be attempted. • Is it possible to invert oriented DCSs to PESs?

  24. Questions? j’ = 4.5, R21

  25. NO-He, P11 (’=1/2, ’=1) j’ = 1.5 j’ = 2.5 j’ = 3.5 j’ = 4.5 j’ = 5.5 j’ = 6.5 j’ = 7.5 j’ = 8.5 j’ = 9.5 j’ = 10.5 j’ = 11.5 j’ = 12.5 12-03-2004

  26. NO-He, P11 (’=1/2, ’=1) j’ = 1.5 j’ = 2.5 j’ = 3.5 j’ = 4.5 j’ = 7.5 j’ = 5.5 j’ = 6.5

  27. NO-He R21 (’=1/2, ’=-1) j’ = 1.5 j’ = 2.5 j’ = 3.5 j’ = 4.5 j’ = 5.5 j’ = 6.5 j’ = 7.5 j’ = 8.5 j’ = 9.5 j’ = 10.5 j’ = 11.5 j’ = 12.5 12-03-2004

  28. NO-He R21 (’=1/2, ’=-1) j’ = 1.5 j’ = 2.5 j’ = 3.5 j’ = 4.5 j’ = 5.5 j’ = 6.5 j’ = 7.5 j’ = 8.5 j’ = 9.5 j’ = 10.5 j’ = 11.5 j’ = 12.5

  29. DCS extraction • Extraction of differential cross sections (dcs’s) from • images (forward deconvolution): • Calculate the center(pixel) of the scattering circle • use intensity on an outer ring of the image as trial dcs • Use the trial dcs to simulate an image • Improve the dcs, minimizing the difference between simulated and measured image • Step 3 and 4 are repeated until the simulated an measured • images correspond well enough.

  30. NO-He R11 Q21 (’=1/2, ’=1) j’ = 1.5 j’ = 2.5 j’ = 3.5 j’ = 4.5 j’ = 5.5 j’ = 6.5 j’ = 7.5 j’ = 8.5 j’ = 9.5 j’ = 10.5 j’ = 11.5 j’ = 12.5 15-03-2004

  31. NO-He Q11 P21 (’=1/2, ’=-1) j’ = 1.5 j’ = 2..5 j’ = 3.5 j’ = 4.5 j’ = 5.5 j’ = 6.5 j’ = 7.5 j’ = 8.5 j’ = 9.5 j’ = 10.5 j’ = 11.5 j’ = 12.5 17-03-2004

  32. NO-He P12 (’=3/2,’=1) j’ = 1.5 j’ = 2..5 j’ = 3.5 j’ = 4.5 j’ = 5.5 j’ = 6.5 j’ = 7.5 j’ = 8.5 j’ = 9.5 j’ = 10.5 j’ = 11.5 j’ = 12.5 15-03-2004

  33. NO-He R22 (’=3/2,’=-1) j’ = 1.5 j’ = 2..5 j’ = 3.5 j’ = 4.5 j’ = 5.5 j’ = 6.5 j’ = 7.5 j’ = 8.5 j’ = 9.5 j’ = 10.5 j’ = 11.5 j’ = 12.5 15-03-2004

  34. NO-He P22 Q12 (’=3/2,’=-1) j’ = 1.5 j’ = 2..5 j’ = 3.5 j’ = 4.5 j’ = 5.5 j’ = 6.5 j’ = 7.5 j’ = 8.5 j’ = 9.5 j’ = 10.5 j’ = 11.5 j’ = 12.5 15-03-2004

  35. NO-He Q22 R12 (’=3/2,’=1) j’ = 1.5 j’ = 2..5 j’ = 3.5 j’ = 4.5 j’ = 5.5 j’ = 6.5 j’ = 7.5 j’ = 8.5 j’ = 9.5 j’ = 10.5 j’ = 11.5 j’ = 12.5 15-03-2004

  36. p’ = p = - 1 p’ = - p = 1 p’ = p = - 1 Experiments A Quasi quantum mechanical treatment yield the following propensity rule depending on the parity These parity-pairs of similar DCSs are also seen in experimental results, the ratios can be verified from HIBRIDON results.

  37. The ratios between differential cross sections within parity pairs, is close to what the Quasi- Quantmum Treatment (QQT) predics. For large j the agreement becomes worse.

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