NO source

1. * * j’ = 1.5 j’ = 1.5 j’ = 2.5 j’ = 2.5 j’ = 3.5 j’ = 3.5 j’ = 4.5 j’ = 4.5 j’ = 5.5 j’ = 5.5 j’ = 6.5 j’ = 6.5 Parity conserving: p’ = - 1 , ’ = 1/2 Parity breaking: p’ = 1, ’ = 1/2 j’ = 8.5 j’ = 8.5 j’ = 8.5 j’ = 8.5 j’ = 9.5 j’ = 9.5 j’ = 10.5 j’ = 10.5 j’ = 11.5 j’ = 11.5 j’ = 12.5 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. Forward ( = 0): Backward ( = ): NO-He collisions: First fully state-selected differential cross sections obtained with ion imaging vrije Universiteit amsterdam Department of Physical Chemistry,De Boelelaan 1083,1081 HV Amsterdam, The Netherlands A.Gijsbertsen, H. Linnartz, J. Klosa, F.J. Aoiza,E.A. Wadeb, D.W. Chandlerb and S. Stolte aDepartamento de Quimica Fisica, Facultad de QuimicaUniversidad Complutense, 28040 Madrid, SpainbCombustion Research Facility, Sandia National Laboratories, Livermore, California 94550, USA 226 nm, 1 mJ He 308 nm, 5 mJ Introduction In our quest to reveal the relation between inelastic collisions and the anisotropy of the inter-molecular potential, important progress has been achieved. Our crossed molecular beam machine has been adapted to allow (1+1’ REMPI) ion-imaging velocity mapping detection. Here we report the first measurements of differential collision cross sections of fully state-selected NO (j =1/2, =1/2,  = -1) with He. A two meters long hexapole is used to obtain full state selection. Full state selection allows for taking a close look at effects of parity conservation and breaking. Experimental setup Hexapole NO NO source Hexapole state selected NO collides with He at Ecoll  510 cm-1: The symmetry index  and the parity p of a rotational state relate as: Crossed 1+1’ REMPI ion imaging detection is applied: molecules are first (resonantly) excited with 226 nm light and then ionized with 308 nm light. He source NO (j=½, =½, =-1) + He  NO ( j’, ’, ’ ) + He dye laser Test To test our setup, some 2% NO was seeded in the He beam. The NO beam consists of 16 % NO in Ar. When tuning the excitation laser to the hexapole selected state, the image reflects the velocity distributions of both pulsed beams. For detection, the ions are accellerated out of the drawing plain and projected onto the detector providing a 2D velocity distribution. XeCl excimer laser vNO Results When tuning the excitation laser to higher rotational states, the images reflect the velocity distributions of the molecules that – after collision with a He atom – are in that particular state. The intensity on an outer ring of the images reflects the differential cross section (DCS). Experimentally obtained NO-He DCS’s are compared to HIBRIDONclose-coupling calculations using Vsum and Vdif on RCCSD(T) Potential Energy Surfaces (PESs) (Klos et al., J. Chem. Phys. 112, 2195 (2000)) in the graphs beneath the images. Experimentally obtained DCS’s are normalized on the (theoretical) total cross sections. vHe Sensitivity: S = 7.7 m/s/pixelNO beam velocity: vNO = 590 +/- 25 m/s He beam velocity: vHe= 1760 +/- 50 m/s • Conclusions and Outlook • Our setup works fine. The use of a hexapole simplifies crossed molecular beam ion imaging experiments! Background signal is minimized as hexapole state selection provides a very clean beam. • Current measurements correspond reasonably well to theory, but are slightly more forward scattered. • Parity breaking transitions show more backward scattering compared to parity conserving collisions. • DCS’s come in parity-pairs: those for excitation to j’ = n, ’ = 1 are similar to DCS’s for j’ = n+1, ’ = -1. • Measurements of the orientation dependence of the DCSs will be attempted. Can one invert oriented DCSs to PESs? Experiment and theory correspond reasonably well indicating that the NO-He PESs is rather accurate. Experimental results show slightly (but significantly) more forward scattering. Note that the DCS’s come in “parity pairs”: two neighboring DCSs (for scattering to j’ = n, ’ = 1 and j’ = n+1, ’ = -1) have a similar shape, although that for j’ = n+1, ’ = -1 is slightly larger.

2. 226 nm, 1 mJ He 308 nm, 5 mJ NO source Hexapole NO He source dye laser XeCl excimer laser 226 nm, 1 mJ He 308 nm, 5 mJ NO source Hexapole NO He source dye laser XeCl excimer laser