3 – 3.5 MIR CRDS 1 – 1.5 NIR CRDS m -HV O2O2 N2N2 OH X a A B X X ~
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 ~ 1.3 m ~ 3 m
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 ~ 1.3 m ~ 3 m ~ 200 NIR Doppler ( slit jet ) ~ 100 MIR D. Anderson, S. Davis, T. Zwier and D. Nesbitt, Chem. Phys. Lett. 258 (1996)207 ~ 200 NIR Doppler ( slit jet ) ~ 100 MIR D. Anderson, S. Davis, T. Zwier and D. Nesbitt, Chem. Phys. Lett. 258 (1996)207
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 MIR D. Anderson, S. Davis, T. Zwier and D. Nesbitt, Chem. Phys. Lett. 258 (1996)207 Doppler ( slit jet ) ~ 100 MIR D. Anderson, S. Davis, T. Zwier and D. Nesbitt, Chem. Phys. Lett. 258 (1996)207
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) Wavenumber (cm -1 ) Absorbance per pass (ppm) using SRS using DFM 0.05 cm 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”)
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 cm -1 = 1.7 s (99.63%) 0 = 5.8 s (99.95%) = 1.0 s (99.98%) 0 = 5.9 s (99.99%)
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) cm 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 Spectrum assignment according to: S. Davis, D. Uy and D. J. Nesbitt, J. Chem. Phys. 112 (2000) 1823 K N K” (N”)
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
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
Main Reactions Related to CH 3, O 2 and O O2O2 CH 3 I Ne
Reactions Products Wavenumber (cm -1 ) Number density (10 13 cm -3 ) CH C 2 H CH CH C 2 H 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
CH 3 I Downstream Injection Without O 2 With O 2 Number density (10 13 cm -3 ) CH ↓0.24 C 2 H ↑0.12 CH ↑0.005 CH ↑0.24 C 2 H ↑0.012 CH 2 O 0.0 ↓ 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
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.
Conclusion & Further work NIR (1.0 – 1.5 m) & MIR (3.0 – 3.5 m) spectra region Near Doppler limited resolution (~200 NIR, <70 MIR) High sensitivity (0.7 x Hz NIR and 1.1 x Hz 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…
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
Discharge Expansions 1) 2) 3) 10 mm 5 mm
Wavenumber (cm -1 ) Ambient CRDS experiment of CH 3 OO JCP. 112 (2000) 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 cm -3 l absorption ~ 16 cm CH 3 OO in the NIR … Absorbance per pass (ppm) S band = 3.7 x cm / mol.