1. Saturation of the NO 2 ν 1 +ν 3 and the CH 4 ν 3 Transitions in Helium Nanodroplets Robert Fehnel Kevin Lehmann Department of Chemistry University of Virginia

2. Why study Saturation of CH 4 and NO 2 ? By studying the saturation of these molecules we will try to understand the line shapes in nanodroplets which are inhomogenous. By studying relaxation we can try and find the inhomogenous relaxation rates Try and understand the relationship between the molecules and a superfluid

3. Nozzle Diameter = 10 μm Skimmer = 400 μm Nozzle T ≥ 16 K Backing Pressure ≤ 60 Bar L He Skimmer Nozzle Closed Circuit Refrigerators He Chopper Pickup cell Multipass Cell 1.5K bolometer N.E.P. ~ 2x10 -14 W/Hz 1/2 10203045cm >5000 L/s 2500 L/s IR OPO 2560 – 3125 cm -1 Machine Schematic Bolometer noise ~ beam noise ~ 10 -5 of chopped beam signal(1 Hz BW)

4. Acculight Argos OPO SPI Wavemeter To Spectrometer OPO Power meter 150 MHz etalon 7.5 GHz etalon Approximately 1.75 W of power measured entering the polarizer and upwards of 0.7W entering the spectrometer. Produces over 2 W of CW over the tunable range of 3.2 – 3.9 μm. Continuous scans of 45 GHz. Also produces 2 - 5 W of 1.5 μm light. MgF 2 Polarizer

5. Perry cell Power Meter The Focal Spot was determined to be 27 µm in diameter. Peak power is equal to 240 kW/cm 2 He Beam Lens

6. Perry Cell Measurements I

7. Perry Cell Measurements 2

8. Beam Quality Singe Pass R 2 = 0.9898

9. Beam Quality Multi Pass R 2 = 0.98015

10. NO 2 spectrum in He ~5000 NO 2 v 1 + v 3 R(0) ->.

11. NO 2 Signal vs Power The R(0) Line is found at 2905.566 cm -1 and the FWHM is 0.035 cm -1.

12. NO 2 Signal vs Power

13. S = a*P/(1+P/P s ) a = 58.954 P s = 0.527 (Χ 2 /(Np-2)) ½ = 0.451

14. NO 2 Signal vs Power S = a*P/(1+P/P s ) a = 58.954 P s = 0.527 (Χ 2 /(Np-2)) ½ = 0.451 S = a*I/((1+P/P s ) ½ ) a = 68.751 P s = 0.117 (Χ 2 /(Np-2)) ½ = 0.651

15. NO 2 Widths

16. Δν = Δν 0 ((1+I/Is) ½ ) Homogenous Case I s = 150 kW/cm 2 Δν 0 = 0.033 (Χ 2 /(Np-2)) ½ = 1.9 x10 -3

17. Methane R(0) Line The R(0) Line is found at 3029.07 cm -1 and the FWHM is 0.20 cm -1.

18. Methane Signal vs Power

19. S = a*P/(1+P/P s ) a = 41.713 P s = 0.458 (Χ 2 /(Np-2)) ½ = 0.152

20. Methane Signal vs Power S = a*P/(1+P/P s ) a = 41.713 P s = 0.458 (Χ 2 /(Np-2)) ½ = 0.152 S = a*P/((1+P/P s ) ½ ) a = 49.723 P s = 0.1 (Χ 2 /(Np-2)) ½ = 0.184

21. Methane Widths

22. Δν = Δν 0 ((1+I/Is) ½ ) Homogenous Case P s = 0.458 Δν 0 = 0.172 (Χ 2 /(Np-2)) ½ = 1.7 x10 -3

23. Results NO 2 CH 4 I s (kW/cm 2 )150130 Transition Dipole (D) 0.050.057 T 1 T 2 (ns 2 )0.310.26 T 1 (ns)1.05.0 T 1 T 2 = (hbar*ε*c)/(2*μ*I s )

24. Results II Knowing that the focal point diameter is 27 µm and the speed of the beam is 450 m/s then we can determine that the NO 2 spends 60ns in each crossing with the beam We believe that by comparing our T 1 time for methane of 5 ns to a previous result by Momose’ group for the v 4 R(0) line of methane which results in a 3.7 ns T 2 time that we are relaxing to the 2v 4 and then to the ground state

25. Conclusions We were able to show saturation with both CH 4 and NO 2 With both species a homogenous and inhomogenous fit worked well for signal Only homogenous line shape fit the widths correctly

26. Future Work This technique could be applied to other similar molecules with similar strong lines such as CH 3 Cl and Propyne Also try to adjust the number of passes while keeping the amount of scattered light low – This could be done by putting the Perry cell on a rotation stage – Also determine saturation by number of passes instead of using polarizer to adjust power

27. Acknowledgements Dr. Ozgur Birer who help construct the HENDI machine at UVa. Funding: National Science Foundation, UVa