1. 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 vrije Universiteit amsterdam a Departamento de Quimica Fisica, Facultad de Quimica,Universidad Complutense, 28040 Madrid, Spain b Combustion Research Facility, Sandia National Laboratories, Livermore, California 94550

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

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

4. SifSif SifSif NO-Ar, E tr  500 cm -1 NO-He, E tr  500 cm -1 Introduction

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

7. 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) Introduction

8. NO source chamber He source XeCl excimer laser dye lase r 308 nm, 5 mJ 226 nm, 1 mJ He Hexapole NO collision chamber Experimental setup Hexapole state selected NO collides with He at E coll  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

14. 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. 50 100 150 200 250 300 150200250300350 200 250 300 350 400 450 Experiments 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. v NO v He

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

17. * 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 * Parity conserving: p’ = p = - 1 Experiments *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. ***** 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 Parity breaking: p’ = - p = 1 Experiments

21. Parity breaking: p’ = - p = 1

22. NO-He P 12 (  ’=3/2,  ’=1) 15-03-2004 j’ = 1.5 j’ = 2..5j’ = 3.5 j’ = 4.5j’ = 5.5 j’ = 6.5 j’ = 7.5 j’ = 8.5j’ = 9.5 j’ = 10.5j’ = 11.5 j’ = 12.5

23. Conclusions and Outlook 1.Ion imaging setup works very well. 2.The use of a hexapole makes crossed beam ion imaging experiments more sensitive and easier instead of more difficult. 3.Our experimental results overall agree with quantum calculations. They show slightly more forward scattering. 4.A propensity rule for the DCS is seen experimentally. 5.Measurements of orientation dependence of the DCSs will be attempted. 6.Is it possible to invert oriented DCSs to PESs?

24. Questions? j’ = 4.5, R 21

28. NO-He, P 11 (  ’=1/2,  ’=1) 12-03-2004 j’ = 1.5 j’ = 2.5 j’ = 3.5 j’ = 4.5 j’ = 5.5 j’ = 6.5 j’ = 7.5 j’ = 8.5j’ = 9.5 j’ = 10.5 j’ = 11.5 j’ = 12.5

29. NO-He, P 11 (  ’=1/2,  ’=1) j’ = 1.5j’ = 2.5j’ = 3.5j’ = 4.5 j’ = 7.5 j’ = 6.5j’ = 5.5

30. 12-03-2004 NO-He R 21 (  ’=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’ = 8.5j’ = 9.5 j’ = 10.5 j’ = 11.5 j’ = 12.5

31. NO-He R 21 (  ’=1/2,  ’=-1) j’ = 11.5 j’ = 1.5j’ = 2.5j’ = 3.5j’ = 4.5 j’ = 8.5j’ = 7.5j’ = 6.5 j’ = 5.5 j’ = 12.5j’ = 10.5j’ = 9.5

32. DCS extraction Extraction of differential cross sections (dcs’s) from images (forward deconvolution): 1.Calculate the center(pixel) of the scattering circle 2.use intensity on an outer ring of the image as trial dcs 3.Use the trial dcs to simulate an image 4.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.

33. NO-He R 11 Q 21 (  ’=1/2,  ’=1) 15-03-2004 j’ = 1.5 j’ = 2.5j’ = 3.5 j’ = 4.5j’ = 5.5 j’ = 6.5 j’ = 7.5 j’ = 8.5j’ = 9.5 j’ = 10.5j’ = 11.5 j’ = 12.5

34. NO-He Q 11 P 21 (  ’=1/2,  ’=-1) 17-03-2004 j’ = 1.5 j’ = 2..5j’ = 3.5 j’ = 4.5j’ = 5.5 j’ = 6.5 j’ = 7.5 j’ = 8.5j’ = 9.5 j’ = 10.5j’ = 11.5 j’ = 12.5

35. NO-He P 12 (  ’=3/2,  ’=1) 15-03-2004 j’ = 1.5 j’ = 2..5j’ = 3.5 j’ = 4.5j’ = 5.5 j’ = 6.5 j’ = 7.5 j’ = 8.5j’ = 9.5 j’ = 10.5j’ = 11.5 j’ = 12.5

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

37. NO-He P 22 Q 12 (  ’=3/2,  ’=-1) 15-03-2004 j’ = 1.5 j’ = 2..5j’ = 3.5 j’ = 4.5j’ = 5.5 j’ = 6.5 j’ = 7.5 j’ = 8.5j’ = 9.5 j’ = 10.5j’ = 11.5 j’ = 12.5

38. NO-He Q 22 R 12 (  ’=3/2,  ’=1) j’ = 1.5 j’ = 2..5j’ = 3.5 j’ = 4.5j’ = 5.5 j’ = 6.5 j’ = 7.5 j’ = 8.5j’ = 9.5 j’ = 10.5j’ = 11.5 j’ = 12.5 15-03-2004

39. 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. Experiments p’ = p = - 1 p’ = - p = 1

40. 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.