Agnés Perrin Laboratoire Interuniversitaire des Systémes Atmosphériques (LISA),

CNRS, Université Paris XII, CréteilAgnes.Perrin@lisa.univ-paris12.fr

C.Bray, D.Jacquemart, N. LacomeLaboratoire de Dynamique, Interactions et Réactivité (LADIR) ,

Université Pierre et Marie Curie-Paris 6, France

Update of methyl Chloride in the 3 µm region

Importance of CH3Cl

• Methyl chloride (CH3Cl) is the most abundant, natural, chlorine-containing gas in the atmosphere, with natural sources like oceans and biomass burning as major identified sources.

Global methyl chloride (CH3Cl) 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 (C2H6) (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}.

Infrared region for CH3Cl (image from the PNNL laboratory) and recent update in

HITRAN

Infrared region for CH3Cl (image from the PNNL laboratory) and recent update in

HITRAN

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)

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

Some Q-branches 1 band

Parts of the (weaker ) 4

and 36 band

Missing: the P- and R-branches of the 1 band

.1: Morillon, Graner J.Mol. Spectr (1969)

.4, 36(l=1) Jensen, Brodenson, Guelachvili, J.Mol.Spect(1981)

Goal of this study for methyl chloride (CH3Cl)

• Perform a new analysis of the 3.3 µm region for methyl chloride (the 35Cl and 37Cl species) positions, intensities and line shape parameters

• New FTS spectra recorded on the Bruker-FTS spectrometer of LADIR for pure CH3Cl and N2- CH3Cl samples

• Analysis of line positions and intensities

Experimental conditions & Analysis• Fourier transform spectra recorded on the Bruker IFS 120

HR (LADIR, Paris) for natural sample of CH3Cl, 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 :

• 35CH3Cl 1, (1176, J 47, K 12); 4, (1532, J 41, K 13), 36 (l=1) (603, J 34, K 5).

• 37CH3Cl 1, (680, J 41, K 7); 4, (405, J 30, K 10) , 36 (l=1) ( 118, J 25, K 4).

Analysis for CH335Cl and CH3

37Cl

parallel

parallel

Perpendicular

Perpendicular

36 (l=1) 4 (l=1) strongly resonating

36 (l=1) and 4 (l=1) resonating with 1 (l=0)

Six resonating states with l=0,1,2 and 3

Dark states 25(l=2), 23+5(l=1) and 36(l=3)

Vibration-rotational |v, J, l, k> with l =0,±1,± 2 and ±3 , and -J k J

< v l J k| | v’, l’ J k’ > resonances accounted for

within the (k- l )= 0 3n « Amat’s » selection rules

Diag part Hamiltonian: E v,l,k= Ev+(A-B)k2+ B.J(J+1)+ A l.kResonances:

within each given vibrational state (v=v’, l l’)between different vibrational states (vv’, 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 …

k|= 25

l =2

23+5

l=1

1

l=04

l=136

l=136

l=3

25 l=2 W 1, 2

23+5

l=1

W 1, 2

1 l=0 1, 2 1, 2 W 1, 2 0,3

4 l=1 1, 2 W 0,1,2 1, 2

36 l=1 0,1,2 W 1, 2

36 l=3 0,3 1, 2 1, 2 W

Resonances < v l J k| | v’, l’ J k’ > in (k-l)=0 3n

|l|=2|l|=1|l|=0 or 3

Line intensities• From a set of 200 experimental line intensities for

the 1 (//-type) 4 and 36(l=1) (╨ type) bands of CH3

35Cl, the transition moment operators 1z and 4x of the 1 & 4 band was determined.

• For the 36(l=1) band: 36x=0

• (for the 23+5, 25(l=2), 36(l=3) dark bands)

• For CH337Cl, same (1z & 4x) transition moment

operator for 1 & 4 than for CH335Cl

10

Forbidden transition from the 23+5 band

Resonance 4(l=1) k=2 36(l=3) k=0

Forbidden transition from the 36 (l=3) dark band

Conclusion• High resolution (Bruker) FTS spectra of natural

CH3Cl were recorded at LADIR.• A large set of line positions and intensities were

measured• A new extended analysis of the 1, 4, 26 bands of

CH335Cl and CH3

37Cl was performed.• The calculations of line positions and intensities

account for numerous resonances coupling the 1, 4,(l=1), 26(l=1) bright states with the 23+5 (l=1), 25(l=2) and 36(l=3) dark states.

• Future ongoing studies involve N2-broadening and line mixing studies.

Financial support from INSU through the LEFE-CHAT program is gratefully acknowledged

Each J-matrix splits into 4 submatrices according to J, k, l

A1 A2 E(3n+1) E(3n+2)

A1

A2

E(3n+1)

E(3n+2)

A1: (k- l)=3n and (J+k+ l ) even A2: (k- l)=3n and (J+k+ l ) odd E3n+1 : (k- l)=3n+1 E3n+2 : (k- l)=3n+2

Exactely degenerate

Vibration-rotational |J, l, K> with l =0, 1, 2 and 3

< v l J k| | v’, l’ J k’ > resonances accounted for within the (k- l )= 0 3n

« Amat’s » selection rule

Diag part Hamiltonian: E v,l,k= Ev+(A-B)K2+ B.J.(J+1)+ A l.k

Resonances: within each given vibrational state (v=v’, for l l’)

between different vibrational states (vv’, for l l’).

A1: (k- l)=3n and (J+k+ l ) even A2: (k- l)=3n and (J+k+ l ) odd E3n+1 : (k- l)=3n+1 E3n+2 : (k- l)=3n+2

Wötzel, Mäder, Harder, Pracna & Sarka, J. Mol. Struct. 780-781, p206 (2006)

degeneracy

Example of a resonance

Analysis

parallel

parallel

Perpendicular

Perpendicular

+ several dark interacting bands…