1. 64th Ohio State University Symposium on Molecular Spectroscopy June 22–26, 2009 THE HIGH RESOLUTION FAR- INFRARED SPECTRUM OF METHANE AT THE SOLEIL SYNCHROTRON Vincent BOUDON Institut Carnot de Bourgogne – UMR 5209 CNRS-Université de Bourgogne, 9 Av. A. Savary, BP 47870, F-21078 DIJON, France Olivier PIRALI, Pascale ROY Ligne AILES – Synchrotron SOLEIL, L’Orme des Merisiers, F-91192, GIF-SUR-YVETTE, France Laurent MANCERON LADIR – UMR 7075 Université Pierre et Marie Curie–CNRS, Case 49, 4 Place Jussieu, F-75252 PARIS, France Jean VANDER AUWERA Service de Chimie Quantique et Photophysique, ULB, CP 160/09, 50 Av. F. D. Roosevelt, F-1050 BRUSSELS, Belgium

2. 64th Ohio State University Symposium on Molecular Spectroscopy June 22–26, 2009 Contents I.The THz spectrum of CH 4 II.Experimental details III.Analysis of line intensities IV.Conclusion

3. 64th Ohio State University Symposium on Molecular Spectroscopy June 22–26, 2009 I. The THz spectrum of CH 4

4. 64th Ohio State University Symposium on Molecular Spectroscopy June 22–26, 2009 The polyads of CH 4

5. 64th Ohio State University Symposium on Molecular Spectroscopy June 22–26, 2009 Centrifugal distortion spectrum CH 4 has no permanent dipole moment Due to the contact transformation, the effective dipole moment up to 1 st order expands as (for cold and hot bands): These parameters can be calculated analytically (Hilico et al. 1987, Loëte 1988)

6. 64th Ohio State University Symposium on Molecular Spectroscopy June 22–26, 2009 Far-infrared CH 4 lines on Titan

7. 64th Ohio State University Symposium on Molecular Spectroscopy June 22–26, 2009 Previous works 1988: First resolved spectra Courtesy A. R. W. McKellar Unpublished results P ~ 36 Torr, T ~ 128 K, Path ~ 20 m Resolution ~ 0.008 cm -1 R branch measured at low resolution and high pressure: Ozier and Rozenberg (1975, 1978) Q branch measured in microwave: Holt et al. (1975), Oldani et al. (1985) – no intensities Theoretical calculation of Hilico et al. (1987), Loëte (1988) R branch reinvestigated by Wishnow et al. (2007), but still at low resolution and high pressure (≥ 1 bar)

8. 64th Ohio State University Symposium on Molecular Spectroscopy June 22–26, 2009 Calculation using STDS

9. 64th Ohio State University Symposium on Molecular Spectroscopy June 22–26, 2009 II. Experimental details

10. 64th Ohio State University Symposium on Molecular Spectroscopy June 22–26, 2009 AILES beamline at SOLEIL High Resolution Absorption Spectroscopy in the Far-IR Synchrotron beam entrance Interferometer Multipass cell : Max = 200m Bolometer detectors Maximum spectral resolution = 0.001 cm -1 Spectral range= 7-1000 cm -1 See Talk TG04

11. 64th Ohio State University Symposium on Molecular Spectroscopy June 22–26, 2009 Experimental conditions Multipass White cell: L = 151.748 m Ambiant temperature (T = 296 K) Pressure / mb9.9120.050.0100.0 Resolution / cm -1 0.00110.0020.0050.010

12. 64th Ohio State University Symposium on Molecular Spectroscopy June 22–26, 2009 Examples of resolved rotational clusters

13. 64th Ohio State University Symposium on Molecular Spectroscopy June 22–26, 2009 Examples of resolved rotational clusters

14. 64th Ohio State University Symposium on Molecular Spectroscopy June 22–26, 2009 Examples of resolved rotational clusters

15. 64th Ohio State University Symposium on Molecular Spectroscopy June 22–26, 2009 III. Analysis of line intensities

16. 64th Ohio State University Symposium on Molecular Spectroscopy June 22–26, 2009 Measurements vs. HITRAN for R(7)

17. 64th Ohio State University Symposium on Molecular Spectroscopy June 22–26, 2009 Fit details: 1 st order dipole moment 0 cm -1 1310 cm -1 1533 cm -1 2 4 Dyad, Hot bands: 114 lines Ground State, Cold band: 100 lines Three different fits: 1.GS – GS (cold band) alone 2.GS – GS and Dyad – Dyad (cold and hot bands) simultaneously 3.Dyad – Dyad (hot band) alone with GS – GS parameter fixed to result of fit 1.

18. 64th Ohio State University Symposium on Molecular Spectroscopy June 22–26, 2009 Fit residuals for the GS–GS fit (fit 1)

19. 64th Ohio State University Symposium on Molecular Spectroscopy June 22–26, 2009 Fit residuals for the simultaneous fit (fit 2) 1.94

20. 64th Ohio State University Symposium on Molecular Spectroscopy June 22–26, 2009 Comparison of the different results

21. 64th Ohio State University Symposium on Molecular Spectroscopy June 22–26, 2009 IV. Conclusion

22. 64th Ohio State University Symposium on Molecular Spectroscopy June 22–26, 2009 What is the “correct” value for  D ? The calculated value (Hilico et al. 1987) is certainly too low The GS–GS fit of high-resolution data gives a slightly lower value than Wishnow et al. (2007) The simultaneous fit of cold and hot bands lowers the  D value, but there maybe some other contributions to take into account for the hot band (higher RMS)  D only contributes marginally to the hot band intensity We thus recommend  D = 23.40 ×10 -6 D ; but measured intensities can now be used (to be published)

23. 64th Ohio State University Symposium on Molecular Spectroscopy June 22–26, 2009 The STDS database Spherical Top Data System www.icb.cnrs.fr/OMR/SMA/SHTDS Molecular parameter database Calculation and analysis programs XTDS : Java interface