2. 3 – 3.5  MIR CRDS 1 – 1.5  NIR CRDS 432 1  m -HV O2O2 N2N2 OH X a A B X X ~

3. SRS configuration Ti:Sa ring cw laser Ti:Sa Amplifier Nd:YAG pulse laser Raman Cell PD InGaAs or InSb Detector Ring-down cavity with slit-jet (absorption length ℓ = 5 cm) L = 67 cm Vacuum Pump 1 m single pass SRS 750 ~ 900 nm 40 ~ 100 mJ  ~ 40 MHz ℓ Nd:YAG cw laser 1 st Stokes, ~ 1.3  m, ~ 2 mJ 2 nd Stokes, ~ 3  m, ~ 200  J  SRS : 180 – 220 MHz Experimental Apparatus R ~ 99.995% @ 1.3  m ~ 99.96% @ 3  m

4. Ti:Sa ring cw laser Ti:Sa Amplifier Nd:YAG pulse laser Raman Cell PD InGaAs or InSb Detector Ring-down cavity with slit-jet (absorption length ℓ = 5 cm) L = 67 cm Vacuum Pump 1 m single pass SRS 750 ~ 900 nm 40 ~ 100 mJ  ~ 40 MHz ℓ Nd:YAG cw laser 1 st Stokes, ~ 1.3  m, ~ 2 mJ 2 nd Stokes, ~ 3  m, ~ 200  J  SRS : 180 – 220 MHz Experimental Apparatus S. Wu, P. Dupre and T. A. Miller, Phys. Chem. Chem. Phys. 8 (2006) 1682 SRS configuration R ~ 99.995% @ 1.3  m ~ 99.96% @ 3  m ~ 200 MHz @ NIR  Doppler ( slit jet ) ~ 100 MHz @ MIR D. Anderson, S. Davis, T. Zwier and D. Nesbitt, Chem. Phys. Lett. 258 (1996)207 ~ 200 MHz @ NIR  Doppler ( slit jet ) ~ 100 MHz @ MIR D. Anderson, S. Davis, T. Zwier and D. Nesbitt, Chem. Phys. Lett. 258 (1996)207

5. Ti:Sa ring cw laser Ti:Sa Amplifier Nd:YAG pulse laser Raman Cell PD InSb Detector Ring-down cavity with slit-jet (absorption length ℓ = 5 cm) L = 67 cm Vacuum Pump 1 m single pass SRS 750 ~ 900 nm 40 ~ 100 mJ  ~ 40 MHz ℓ Nd:YAG cw laser DFM configuration Experimental Apparatus DFM unit Nd:YAG pulse laser 1064 nm (9398 cm -1 ), ~ 150 mJ ~ 3.3  m, 600  J,  DFM : < 70 MHz  Doppler ( slit jet ) ~ 100 MHz @ MIR D. Anderson, S. Davis, T. Zwier and D. Nesbitt, Chem. Phys. Lett. 258 (1996)207  Doppler ( slit jet ) ~ 100 MHz @ MIR D. Anderson, S. Davis, T. Zwier and D. Nesbitt, Chem. Phys. Lett. 258 (1996)207

6. The Comparison of CH 3 Spectra ( 3 band ) P Q 1 (2) P Q 1 (1) R R 0 (0) P Q 2 (2) R R 1 (1) P R 1 (1) 3165.01 3165.44 3174.30 3175.43 3182.86 3203.30 Wavenumber (cm -1 ) Absorbance per pass (ppm) using SRS using DFM 0.05 cm -1 370 MHz 150 MHz 240 MHz 105 MHz Spectrum assignment according to: T. Amano, P. F. Bernath, C. Yamada, Y. Endo and E. Hirota, J. Chem. Phys. 77 (1982) 5284 S. Davis, D. T. Anderson, G. Duxbury and D. J. Nesbitt, J. Chem. Phys. 107 (1997) 5661  K  N K” (N”)

7. Non-exponential Decay  laser > =  Doppler  The beginning of the decay reflects the medium absorption  The end of the decay reflects the empty cavity absorption The non-linear response of the absorption medium  The absorption is saturated at the very beginning of the decay  The later part of the decay is approximated by the linear absorption The chemical or physical dynamics faster than    Multi-exponential decay  To analyze the decay as a function of time t (  s) Intracavity Energy (  J ) Empty cavity CH 3 [ R R 0 (0) ] absorption Empty cavity CH 3 [ R R 0 (0) ] absorption SRS radiation DFM radiation Decay curve @ 3174.295 cm -1  = 1.7  s (99.63%)  0 = 5.8  s (99.95%)  = 1.0  s (99.98%)  0 = 5.9  s (99.99%)

8. Spectra of Jet- Cooled CRDS (DFM version) P, Q and R branch of 3 band of methyl radical (CH 3 ) Absorbance per pass (ppm) R R 0 (0) R R 1 (1) R R 2 (2) R R 3 (3) P R 1 (1) P Q 1 (1) P P 1 (1) P P 2 (2) P P 3 (3) 3128.55 3137.56 3146.50 3165.44 3174.30 3182.86 3191.34 3199.74 3203.30 0.05 cm -1 3127 3167 3207 Wavenumber (cm -1 ) E rot (cm -1 ) T = 19 (2) K I / Honl-London Fac. Wavenumber (cm -1 ) Absorbance per pass (ppm) R branch 1 (K=0) band of ethyl radical (C 2 H 5 ) I / Honl-London Fac. E rot (cm -1 ) T = 18 (2) K 0 1 2 3 4 5 6 7 Spectrum assignment according to: S. Davis, D. Uy and D. J. Nesbitt, J. Chem. Phys. 112 (2000) 1823  K  N K” (N”)

9. Discharge Expansions - HV Longitudinal DischargeTransverse Discharge R R 0 (0) 3 band CH 3 I CH 3 I Ne peak absorbance per pass ( 200 mA discharge ) 1800 ppm1700 ppm Max. stable discharge current 200 mA (1800 ppm) 400 mA (2000 ppm) Noise ( at max. discharge current ) 7 ppm5 ppm S/N ~ 400 S/N ~ 250

10. Discharge Expansions - HV Longitudinal DischargeTransverse Discharge CH 3 I CH 3 I Ne R R 0 (0) 3 band peak absorbance per pass ( 200 mA discharge ) 1800 ppm1700 ppm Max. stable discharge current 200 mA (1800 ppm) 400 mA (2000 ppm) Noise ( at max. discharge current ) 7 ppm5 ppm Downstream injectionNoYes O2O2 O2O2 O2O2 -HV S/N ~ 400 S/N ~ 250

11. Main Reactions Related to CH 3, O 2 and O O2O2 CH 3 I Ne

12. Reactions Products 28502950305031503250 Wavenumber (cm -1 ) Number density (10 13 cm -3 ) CH 3 1.2 C 2 H 6 0.30 CH 4 0.010 CH 3 0.12 C 2 H 6 0.048 CH 2 O 0.79 Without O 2 With O 2 10 mm 0.8 mm CH 3 OO 0.15 O2O2 A. Perrin, A. Valentin, L. Daumont, J. Mol. Struc. 780–781 (2006) 28 CH 3 I Ne

13. CH 3 I Downstream Injection Without O 2 With O 2 Number density (10 13 cm -3 ) CH 3 0.96 ↓0.24 C 2 H 6 0.42 ↑0.12 CH 4 0.015 ↑0.005 CH 3 0.36 ↑0.24 C 2 H 6 0.05 ↑0.012 CH 2 O 0.0 ↓0.79 10 mm 0.8 mm R R 0 (0) 3 band Absorbance (ppm) Wavenubmer (cm -1 ) time (s) Absorbance (ppm) N 2 or Ne injection O 2 injection 25% CH 3 OO 0.3 ↑0.15 O2O2 or N2N2 Ne O2O2

14. Candidate for Jet-cooled spectra of CH 3 OO at NIR Wavenumber (cm -1 ) Absorption per pass (ppm) Prediction at 20 K CH 3 I as precursor O 2 downstream inject. Scan #1 Scan #2 CH 3 COCH 3, as precursor O 2 downstream inject.

15. Conclusion & Further work NIR (1.0 – 1.5  m) & MIR (3.0 – 3.5  m) spectra region Near Doppler limited resolution (~200 MHz @ NIR, <70 MHz @ MIR) High sensitivity (0.7 x 10 -7 Hz -1/2 @ NIR and 1.1 x 10 -6 Hz -1/2 @ MIR) Transverse discharge with capability of downstream injection Candidate for jet-cooled spectra of CH 3 OO was found in NIR Rotational structure of CH 3 OO Other interesting radicals…

16. Acknowledgement  Dr. Terry A. Miller  Current group members: Patrick Rupper, Gabriel Just, Jinjun Liu, Erin Sharp, Ilias Sioutis and Becky Gregory.  Former group members: John Yi and Vadim Stakhursky &  Group in mechanical engineering: Dr. J. William Rich, Dr. Igor V. Adamovich, Yurii Utkin &  Colleagues in machine shop: Jerry Hoff, Larry Antal, Joshua Shannon  Colleagues in electronic shop: Dale Karweik, John Sullivan & NSF Funding

17. Discharge Expansions 1) 2) 3) 10 mm 5 mm

18. Wavenumber (cm -1 ) Ambient CRDS experiment of CH 3 OO JCP. 112 (2000) 10695 Simulation  Doppler = 0.2 cm -1 T = 293 K Simulated Jet-Cooled CRDS of CH 3 OO  = 0.01 cm -1 T = 20 K N obs ~ 1.5 x 10 15 cm -3 l absorption ~ 16 cm CH 3 OO in the NIR … Absorbance per pass (ppm) S  band = 3.7 x 10 -19 cm / mol.