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

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

Outline

Introduction

La se r b e a m

Prim a ry b e a m va lve (16 % N O /Ar)

Se c o nd a ry b e a m Va lve (Ar)He xa p o le sta te se le c to r

Le ns syste m a ndp ho to m ultip lie r

O rie nta tio n fie ldLig ht b a ffle s

oriented 21/2 NO ( j = ½, = -1) + R

21/2 NO ( j’,’,’ ) + R

With R = Ar, He, D2,...

Sif

Sif

NO-Ar, Etr 500 cm-1

NO-He, Etr 500 cm-1

Introduction

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.

j’=7.5

Westley et al., J. Chem. Phys. 114, 2669 (2001)

Differential cross section He-NO (Sandia)

Introduction

Th.

Ex.

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

NO source chamber

He source

XeCl excimer laser

dye laser

308 nm, 5 mJ

226 nm, 1 mJ He

Hexapole

NO

collision chamber

Experimental setup

Hexapole state selected NO collides with He at Ecoll 500 cm-1:

Crossed 1+1’ REMPI detection

excitation 226 nmionization 308 nm

NO (j=½, =½, =-1) NO ( j’, ’, ’ )

Ion imaging

Ion imaging:

Measure a velocity distribution for every rotational state of the NO molecules after collision.

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MCP + Phosphor screen

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+ CCD camera

velocity mapping

ions

Extractor MCP's

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velocity mapping

ions

Extractor MCP's

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velocity mapping

ions

Extractor MCP's

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velocity mapping

ions

Extractor MCP's

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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.

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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.

vNO

vHe

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)

Some parameters

Forward scattering ( = 0): Backward scattering ( = ):

vNO

vHe

*

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.

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.

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TheoryExperiment

j = 1 j = 2 j = 3 j = 4

j = 5 j = 6 j = 7 j = 8

j = 9 j = 10 j = 11 j = 12

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

Parity breaking: p’ = - p = 1

Experiments

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j = 1 j = 2 j = 3 j = 4

j = 8 j = 7 j = 6 j = 5

j = 9 j = 10 j = 11 j = 12

Experiments

Parity breaking: p’ = - p = 1

NO-He P12 (’=3/2, ’=1)

15-03-2004

j’ = 1.5 j’ = 2..5 j’ = 3.5 j’ = 4.5 j’ = 5.5 j’ = 6.5

j’ = 7.5 j’ = 8.5 j’ = 9.5 j’ = 10.5 j’ = 11.5 j’ = 12.5

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?

Questions?

j’ = 4.5, R21

NO-He, P11 (’=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’ = 8.5 j’ = 9.5 j’ = 10.5 j’ = 11.5 j’ = 12.5

NO-He, P11 (’=1/2, ’=1)

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j’ = 1.5 j’ = 2.5 j’ = 3.5 j’ = 4.5

j’ = 7.5j’ = 6.5j’ = 5.5

12-03-2004

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

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j’ = 11.5

j’ = 1.5 j’ = 2.5 j’ = 3.5 j’ = 4.5

j’ = 8.5j’ = 7.5j’ = 6.5

j’ = 5.5

j’ = 12.5j’ = 10.5j’ = 9.5

DCS extraction

Extraction of differential cross sections (dcs’s) fromimages (forward deconvolution):

1. Calculate the center(pixel) of the scattering circle2. use intensity on an outer ring of the image as trial dcs

3. Use the trial dcs to simulate an image4. 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.

NO-He R11 Q21 (’=1/2, ’=1)

15-03-2004

j’ = 1.5 j’ = 2.5 j’ = 3.5 j’ = 4.5 j’ = 5.5 j’ = 6.5

j’ = 7.5 j’ = 8.5 j’ = 9.5 j’ = 10.5 j’ = 11.5 j’ = 12.5

NO-He Q11 P21 (’=1/2, ’=-1)

17-03-2004

j’ = 1.5 j’ = 2..5 j’ = 3.5 j’ = 4.5 j’ = 5.5 j’ = 6.5

j’ = 7.5 j’ = 8.5 j’ = 9.5 j’ = 10.5 j’ = 11.5 j’ = 12.5

NO-He P12 (’=3/2, ’=1)

15-03-2004

j’ = 1.5 j’ = 2..5 j’ = 3.5 j’ = 4.5 j’ = 5.5 j’ = 6.5

j’ = 7.5 j’ = 8.5 j’ = 9.5 j’ = 10.5 j’ = 11.5 j’ = 12.5

NO-He R22 (’=3/2, ’=-1)

15-03-2004

j’ = 1.5 j’ = 2..5 j’ = 3.5 j’ = 4.5 j’ = 5.5 j’ = 6.5

j’ = 7.5 j’ = 8.5 j’ = 9.5 j’ = 10.5 j’ = 11.5 j’ = 12.5

NO-He P22 Q12 (’=3/2, ’=-1)

15-03-2004

j’ = 1.5 j’ = 2..5 j’ = 3.5 j’ = 4.5 j’ = 5.5 j’ = 6.5

j’ = 7.5 j’ = 8.5 j’ = 9.5 j’ = 10.5 j’ = 11.5 j’ = 12.5

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

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

p’ = - p = 1

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.