1. DIODE-LASER AND FOURIER-TRANSFORM SPECTROSCOPY OF 14 NH 3 AND 15 NH 3 IN THE NEAR-INFRARED (1.5 µm) Nofal IBRAHIM, Pascale CHELIN, Johannes ORPHAL Laboratoire Interuniversitaire des Systèmes Atmosphériques (LISA) Université de Paris-XII, 91405 Créteil Cedex, France CARLOS E. FELLOWS Laboratorio de Espectroscopia e Laser Universidade Federal Fluminense, Niteroi, Rio de Janeiro, Bresil

2. CNRS-LISAMSS 2006, Columbus, June 19-23, 20062 NH 3 : strong bands in the near IR o With a short cell (30 cm) and a few mbar of NH 3, one can achieve optical densities higher than 1 for the strongest lines. → Useful for calibration of NIR spectra NH 3 is also an atmospheric trace gas and present in the atmospheres of the giant planets → NIR useful for concentration determination 1. Motivation 1. Motivation Precise spectral line parameters are needed!

3. CNRS-LISAMSS 2006, Columbus, June 19-23, 20063 Goal: Photo-Acoustic Spectroscopy (PAS) and detection limits of NH 3 around 1.5 µm However: significant problems with line positions and intensities wrt. the literature (Lundsberg-Nielsen et al., JMS 1993) Solution: new FTS spectra recorded at Orsay New NH 3 linelist has already been used by other groups (R. Lees, M. Okumura, …) 2. This work

4. CNRS-LISAMSS 2006, Columbus, June 19-23, 20064 External Cavity Diode Lasers: available from telecommunication 3. ECDL 3. ECDL Fast: one scan (0.5-1.0 cm -1) in a few seconds And: Relatively cheap ! Linewidth 1 MHz (0.00003 cm -1 ) Power 30 mW Tunable range: 1535 – 1565 nm (6390 – 6515 cm-1)

5. CNRS-LISAMSS 2006, Columbus, June 19-23, 20065 Photo-Acoustic Spectroscopy (PAS) 4. PAS 4. PAS Thanks to Prof. Th. Huet, University of Lille, France Photoacoustic effect: Collisional energy transfers Laser tuned to a molecular transition:  Excited molecules  Partly, non radiative de-excitation  Temperature changes  Pressure changes  Acoustic wave  Detection by microphone

6. CNRS-LISAMSS 2006, Columbus, June 19-23, 20066 Simultaneous measurement of NH 3 by direct absorption using a White-type cell 5. Our PAS set-up 5. Our PAS set-up

7. CNRS-LISAMSS 2006, Columbus, June 19-23, 20067 Simultaneous measurement of NH 3 by direct absorption using a White-type cell 5. Our PAS set-up 5. Our PAS set-up

8. CNRS-LISAMSS 2006, Columbus, June 19-23, 20068 6. Results 6. Results Photo-acoustic spectroscopy (PAS) Direct absorption spectroscopy FTS spectra ( 14 NH 3 and 15 NH 3 )

9. CNRS-LISAMSS 2006, Columbus, June 19-23, 20069 6. Results : 1. PAS 6. Results : 1. PAS S/N > 1000

10. CNRS-LISAMSS 2006, Columbus, June 19-23, 200610 6. Results : 1. PAS 6. Results : 1. PAS Spectral calibration using the line list (FTS) of Lundsberg-Nielsen et al. (1993) Problem: different relative line intensities: lines 2 and 3 should be very similar (60% of the line 1 !!!) Check with direct absorption !

11. CNRS-LISAMSS 2006, Columbus, June 19-23, 200611 6. Results : 2. Direct absorption spectroscopy 6. Results : 2. Direct absorption spectroscopy

12. CNRS-LISAMSS 2006, Columbus, June 19-23, 200612 6. Results : 2. Direct absorption spectroscopy 6. Results : 2. Direct absorption spectroscopy

13. CNRS-LISAMSS 2006, Columbus, June 19-23, 200613 6. Results : 2. Direct absorption spectroscopy 6. Results : 2. Direct absorption spectroscopy P = 0.01 Torr (pure Doppler lines)

14. CNRS-LISAMSS 2006, Columbus, June 19-23, 200614 6. Results : 2. Direct absorption spectroscopy 6. Results : 2. Direct absorption spectroscopy Spectral calibration using the line list (FTS) of Lundsberg-Nielsen et al. (1993) Problem: relative line intensities still do not agree: lines 2 and 3 should be very similar (60% of the line 1) – so what is going on here ??? The Doppler widths are not the same !

15. CNRS-LISAMSS 2006, Columbus, June 19-23, 200615 7. Results : Solving the puzzle 7. Results : Solving the puzzle Spectral calibration using the line list (FTS) of Lundsberg-Nielsen et al. (1993) The Doppler widths are not the same ! ? Record new FTS spectra !

16. CNRS-LISAMSS 2006, Columbus, June 19-23, 200616 8. New spectra using FTS 8. New spectra using FTS Experimental conditions: Bruker IFS 120 HR Fourier spectrometer (Orsay) Absorption cell 25 cm, CaF 2 windows NH 3 pressure 30 mbar Spectral range 5950 – 7850 cm -1 Spectral resolution 0.02 cm -1

17. CNRS-LISAMSS 2006, Columbus, June 19-23, 200617 8. 14 NH 3 vs 15 NH 3 8. 14 NH 3 vs 15 NH 3 14 NH 3 15 NH 3

18. CNRS-LISAMSS 2006, Columbus, June 19-23, 200618 8. Comparison of line positions 8. Comparison of line positions 14 NH 3 15 NH 3 Line No. Lundsberg- Nielsen et al. JMS 162 (1993) This work (FTS) (*) Difference in cm -1 16528.7646528.75850.0055 26528.8946528.88280.0112 36529.1846529.17660.0074 (*) calibrated using the IUPAC recommended H 2 O lines of Toth, accuracy (RMS) 0.0005 cm -1

19. CNRS-LISAMSS 2006, Columbus, June 19-23, 200619 One problem remains (PAS)

20. CNRS-LISAMSS 2006, Columbus, June 19-23, 200620 9. Conclusion New list of 14 NH 3 and 15 NH 3 line positions (and intensities) in the NIR around 1.5 microns * NIR photoacoustic spectroscopy can be used for quantitative measurements but needs calibration for each individual line (may be molecule dependent) * The list is available in digital format upon request to the authors. We wish to thank Professors Ron Lees and Li-Hong Xu from New Brunswick (Canada) for very helpful discussions.