1. Cavity Ring Down: Absorption of H-D at 90K
Carlos E. Manzanares Department of Chemistry & Biochemistry Baylor University Waco, Texas 76798

2. Acknowledgements Baylor University
Yasnahir Perez Delgado Helena Diez y Riega
David Camejo Jenny Barroso
Universidad Simon Bolivar, Caracas, Venezuela:
Dr. Mary C. Salazar, Dr. Antonio J. Hernandez
The Robert A. Welch Foundation

3. Ground State Potential Energy Curve
600 nm

4. Earth-Titan Comparison

5. Atmospheric Chemistry

6. Earth: Temperature Profile

7. Titan

8. Titan’s Atmosphere

9. How to obtain σ(l) Experimental: Multipass ‘White’ Cell
Experimental: Cavity Ring Down
Theoretical: Calculations of Overtone Intensities

10. PS-CRD Signal

11. Experimental Technique

12. Low Temperature Cryostat

13. Off-Axis Alignment

14. Stable Off-Axis Path Conditions
The angle of a round trip rotation of the beam spot (2θ)
Cos θ = 1-L/r
L is the mirror spacing
r is the mirror radius of curvature
The reentrant condition is:
2m θ =2n 
m is the number of optical round-trip passes
n is an integer, after every m round trips the ray starts to retrace its path.
D. R. Herriot, H. Kogelnik, R. Kompfner, Appl. Opt. 3 (1964) 523.
Y.A. Bakhirkin, A. A. Kosterev, C. Roller, R. F. Curl, F. K. Tittel, Appl. Opt. 43 (2004) 2257.

15. Free Spectral Range (FSR) Dn =c/2Lm

16. Comparison between Dnoff-axis and Dnon-axis

17. Methane

18. H-D Transition (v = 04) at 298K

19. H-D Transition (v = 04) at 90K

20. H-D R(1) Integrated absorption versus density

21. Summary
A low temperature cavity ring down spectrometer has been constructed to obtain high vibrational overtone spectra of molecules.
Experiments at low pressures and low temperatures (10-200K) provide σ() values simulating atmospheric conditions.

22. Baylor Sciences Building