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
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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,
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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)
*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.