1. FE06 : Collisional Cross- Sections at Low Temperatures David L. Graff T. J. Ronningen F. C. De Lucia The Ohio State University

2. Low Energy Molecular Interactions

4. Typical Cross-Section as a Function of Temperature

5. Doppler Width –Std Dev < 1.5% Temperature –Std Dev < 3% Molecular Thermometry Low Temperature Molecules

6. Analysis: Extract from each Lineshape Line Shape Parameter Pressure Dependence Temperature Dependence Line Origin Independent Doppler Width IndependentSquare root Line Center Linear shiftNot analytical Lorentzian Width Linear increaseNot analytical

7. HC 14 N - He : Broadening / Shifting Experimental errors were reduced to 3% Data are compared to three PES Ronningen et al. JCP 122 184319 (2005)

8. Translation Stage P2P2 P1P1

9. Adjust Mirror Until Absorption “Fits” 0 Steps-2 Steps2 Steps

10. Fit Each Lineshape for Dispersion Functional Form is Voigt Absorption plus Lorentzian Dispersion term –Each term has the same line-center and Lorentzian linewidth

11. Include Dispersion in the Fit

12. Comparison of Methods The two analyses do not yield the same answer

13. Compare Cross-Sections Temp (K)Broadening (A 2 )Shifting (A 2 )Broadening (A 2 )Shifting (A 2 ) 2.0117.1(0.5)-0.8(1.0)17.0(0.4)0.5(1.9) 2.4718.8(0.6)-1.1(1.3)19.4(0.4)0.7(2.0) 3.1420.7(0.6)-0.5(1.5)21.6(0.4)0.3(2.2) 4.2123.0(0.7)-0.8(1.7)22.9(0.5)0.0(2.6) HC 15 NHC 14 N

14. Conclusions Low temperature pressure broadening measurements continue to disagree with theoretical predictions Careful consideration of our experimental variables have sharpened this difference We have improved our method of measuring the pressure shift parameter to gain greater precision

15. Acknowledgements Co-Authors –T.J. Ronningen –Frank De Lucia De Lucia Group –Brenda, Manfred –Ivan, Atsuko –Sarko, Kerra and Corey Funding –ARO and NSF

16. CaH Buffer Gas Trapping CaH -He(3) PES was calcuated by Balakrishnan et. Al. Diffusion rate was measured to be 2-8 times less than predicted values

17. Doppler Width as Thermometer Standard deviation of retrieved Doppler width from thermometer measurement is < 1.5% This corresponds to < 3% standard deviation in Temperature measurement

18. Linewidths retrieved from data simulated with incorrect transpiration corrections were not linear with pressure

19. CO - He : Broadening / Shifting Measurements extended from 1 - 600K Thachuk et al. compared data with four PES Agreement was very good down to 20K Thachuk et al. JCP 105 4005

20. CO - He : Broadening / Shifting Measurements extended from 1 - 600K Thachuk et al. compared data with four PES Agreement was very good down to 20K Thachuk et al. JCP 105 4005

21. Measured both Pressure Broadening / Shifting and Inelastic Depopulation Rates Substantial Disagreement Below 10K Ball, et al. JCP 111 8893 H 2 S - He : Broadening / Shifting

22. HCN - He Pressure Broadening