1. Agnés Perrin Laboratoire Interuniversitaire des Systémes Atmosphériques (LISA), CNRS, Université Paris XII, Créteil Agnes.Perrin@lisa.univ-paris12.fr C.Bray, D.Jacquemart, N. Lacome Laboratoire de Dynamique, Interactions et Réactivité (LADIR), Université Pierre et Marie Curie-Paris 6, France Update of methyl Chloride in the 3 µm region

2. Importance of CH 3 Cl Methyl chloride (CH 3 Cl) is the most abundant, natural, chlorine-containing gas in the atmosphere, with natural sources like oceans and biomass burning as major identified sources.

3. Global methyl chloride (CH 3 Cl) measurements at 3µm Recently solar occultation measurements performed at 3 µm by the ACE-FTS experiment on the SCISAT-1 satellite were used to get the first global distribution of methyl chloride in the upper troposphere and stratosphere. However it was mentioned that the methyl chloride line parameters are of very low quality at 3 µm in both the HITRAN or GEISA databases At 3 µm interferences exist between lines from Methyl chloride and Ethane (C 2 H 6 ) (G.C.Toon) N.Weigum, C.Mcelcheran, K.A.Walker,J.R.Taylor, G.C.Toon, G.Manney and Y.Wang, TI09 64th Molecular Symposium, Columbus 2009}.

4. Infrared region for CH 3 Cl (image from the PNNL laboratory) and recent update in HITRAN

5. A.Nikitin, J.P.Champion, and H. Bürger, J. Mol. Spectrosc. 230, 174 (2005) A.Nikitin J.Mol. Spect 252, 17 (2008) A.Nikitin and J.P.Champion, J. Mol. Spect 230, 168 (2005) A.Nikitin et al. J. Mol Spect 221, 199 (2003)

6. Recent update in the HITRAN database A.Nikitin, J.P.Champion, and H. Bürger, J. Mol. Spectrosc. 230, 174 (2005) A.Nikitin J.Mol. Spect 252, 17 (2008) A.Nikitin and J.P.Champion, J. Mol. Spect 230, 168 (2005) Spectral region used by the ACE-FTS measurements Need to be updated

8. Some Q-branches 1 band Parts of the (weaker ) 4 and 3 6 band Missing: the P- and R-branches of the 1 band. 1 : Morillon, Graner J.Mol. Spectr (1969). 4, 3 6 ( l =1) Jensen, Brodenson, Guelachvili, J.Mol.Spect(1981)

9. Goal of this study for methyl chloride (CH 3 Cl) Perform a new analysis of the 3.3 µm region for methyl chloride (the 35 Cl and 37 Cl species) positions, intensities and line shape parameters New FTS spectra recorded on the Bruker- FTS spectrometer of LADIR for pure CH 3 Cl and N 2 - CH 3 Cl samples Analysis of line positions and intensities

10. Experimental conditions & Analysis Fourier transform spectra recorded on the Bruker IFS 120 HR (LADIR, Paris) for natural sample of CH 3 Cl, T=297K, 2830-3200 cm -1, R=0.008 cm -1.  Path length= 30cm, 0.5  P  15.4 hPascal, (7 spectra), with one spectrum for P=0.5 hPascal & path length =415 cm.  Analysis of line positions and intensities for ~ 4500 assigned lines : 35 CH 3 Cl 1, (1176, J  47, K  12); 4, (1532, J  41, K  13), 3 6 (l=1) (603, J  34, K  5). 37 CH 3 Cl 1, (680, J  41, K  7); 4, (405, J  30, K  10), 3 6 (l=1) ( 118, J  25, K  4).

11. Analysis for CH 3 35 Cl and CH 3 37 Cl parallel Perpendicular

14. 3 6 ( l =1)  4 ( l =1) strongly resonating 3 6 ( l =1) and 4 ( l =1) resonating with 1 ( l =0) Six resonating states with l =0,1,2 and 3 Dark states 2 5 ( l =2), 2 3 + 5 ( l =1) and 3 6 ( l =3)

15. Vibration-rotational |v, J, l, k> with l =0,±1,± 2 and ±3, and -J  k  J resonances accounted for within the  (k- l )= 0  3n « Amat’s » selection rules Diag part Hamiltonian: E v, l,k = E v +(A-B)k 2 + B.J(J+1)+ A  l.k Resonances:  within each given vibrational state (v=v’, l  l ’ )  between different vibrational states (v  v’, l  l ’ ). Wötzel, Mäder, Harder, Pracna & Sarka, J. Mol. Struct. 780-781, p206 (2006) Pracna, Müller, Urban, Horneman, & Klee, J. Mol. Spect. 256, p152 (2009). l ’- l =+1  k’-k= -2, + 1, +4… l ’- l =+2  k’-k= -1, +2, -4,... l ’- l =±3  k’-k= 0, ±3, …. l ’- l =- 1  k’-k=+2, -1, -4 … l ’- l =-2  k’-k= 1, -2, +4 …

16.  k|= 2 5 l =2 2 3 + 5 l =1 1 l =0 4 l =1 3 6 l =1 3 6 l =3 2 5 l =2 W1, 2 2 3 + 5 l =1 W1, 2 1 l =0 1, 2 W 0,3 4 l =1 1, 2W0,1,21, 2 3 6 l =1 0,1,2W1, 2 3 6 l =3 0,31, 2 W Resonances in  (k- l )=0  3n  | l |=2  | l |=1  | l |=0 or 3

17. Line intensities From a set of 200 experimental line intensities for the 1 (//-type) 4 and 3 6 ( l =1) (╨ type) bands of CH 3 35 Cl, the transition moment operators 1  z and 4  x of the 1 & 4 band was determined. For the 3 6 ( l =1) band: 3 6  x =0 (  for the 2 3 + 5, 2 5 ( l =2), 3 6 ( l =3) dark bands) For CH 3 37 Cl, same ( 1  z & 4  x ) transition moment operator for 1 & 4 than for CH 3 35 Cl

19. 10

22. Forbidden transition from the 2 3 + 5 band

26. Resonance 4 (l=1) k=2  3 6 (l=3) k=0 Forbidden transition from the 3 6 ( l =3) dark band

27. Conclusion High resolution (Bruker) FTS spectra of natural CH 3 Cl were recorded at LADIR. A large set of line positions and intensities were measured A new extended analysis of the 1, 4, 2 6 bands of CH 3 35 Cl and CH 3 37 Cl was performed. The calculations of line positions and intensities account for numerous resonances coupling the 1, 4,( l =1), 2 6 ( l =1) bright states with the 2 3 + 5 ( l =1), 2 5 ( l =2) and 3 6 ( l =3) dark states. Future ongoing studies involve N 2 -broadening and line mixing studies. Financial support from INSU through the LEFE-CHAT program is gratefully acknowledged

28. Each J-matrix splits into 4 submatrices according to J, k, l A1A1 A2A2 E (3n+1) E (3n+2) A1A1 A2A2 E (3n+1) E (3n+2) A1: (k- l )=3n and (J+k+ l ) even A2: (k- l )=3n and (J+k+ l ) odd E 3n+1 : (k- l )=3n+1 E 3n+2 : (k- l )=3n+2 Exactely degenerate

29. Vibration-rotational |J, l, K> with l =0, 1, 2 and 3 resonances accounted for within the  (k- l )= 0  3n « Amat’s » selection rule Diag part Hamiltonian: E v, l,k = E v +(A-B)K 2 + B.J.(J+1)+ A  l.k Resonances:  within each given vibrational state (v=v’, for l  l ’)  between different vibrational states (v  v’, for l  l ’). A1: (k- l )=3n and (J+k+ l ) even A2: (k- l )=3n and (J+k+ l ) odd E 3n+1 : (k- l )=3n+1 E 3n+2 : (k- l )=3n+2 Wötzel, Mäder, Harder, Pracna & Sarka, J. Mol. Struct. 780-781, p206 (2006) degeneracy

30. Example of a resonance

31. Analysis parallel Perpendicular + several dark interacting bands…