The The 11 and and 66 bands of diiodo- bands of diiodo-

methane CHmethane CH22II22 around 3.3 around 3.3 m m

studied by high-resolution FTS studied by high-resolution FTS J. Orphal, N. IbrahimJ. Orphal, N. Ibrahim

Laboratoire Interuniversitaire des Systèmes AtmosphériquesLaboratoire Interuniversitaire des Systèmes Atmosphériques

CNRS UMR 7583, Universités Paris-7 et -12CNRS UMR 7583, Universités Paris-7 et -12

Créteil / Paris, FranceCréteil / Paris, France

C. E. FellowsC. E. FellowsLaboratorio de Espectroscopia e LaserLaboratorio de Espectroscopia e Laser

Universidade Federal FluminenseUniversidade Federal Fluminense

Niteroi / Rio de Janeiro, BrazilNiteroi / Rio de Janeiro, Brazil

1. Motivation1. Motivation

Diiodomethane is an important source of Diiodomethane is an important source of tropospheric iodine in marine environmenttropospheric iodine in marine environment

CHCH22II22 is photolysed by sunlight and provides is photolysed by sunlight and provides iodine atoms that react with Oiodine atoms that react with O33 and HO and HOxx species species

small traces of iodine-containing species can small traces of iodine-containing species can play a very important role in the stratosphere play a very important role in the stratosphere since the potential of iodine species for catalytic since the potential of iodine species for catalytic ozone depletion is much higher than that of their ozone depletion is much higher than that of their Cl and Br analogs (because of the much faster Cl and Br analogs (because of the much faster kinetics of I chemistry)kinetics of I chemistry)

1. Motivation1. MotivationMarine aerosol produced from IOMarine aerosol produced from IOxx chemistry chemistry

Laboratory studies are required Laboratory studies are required spectroscopy spectroscopy

OSU 1996

1. Motivation1. Motivation

Nature, June 2002

1. Motivation1. MotivationTropospheric NO2 from GOME

1. Motivation1. Motivation

2. Previous studies of CH2. Previous studies of CH22II22

Kisiel et al. (JCP 1996, JMS 2000)Kisiel et al. (JCP 1996, JMS 2000)– Ground-state rotational constantsGround-state rotational constants

– Analysis of the vAnalysis of the v44=n excited states=n excited states

2. Previous studies of CH2. Previous studies of CH22II22

Kisiel et al., JMS, 2000

2. Previous studies of CH2. Previous studies of CH22II22

Kisiel et al., JMS, 2000

2. Previous studies of CH2. Previous studies of CH22II22

Kisiel et al. (JCP 1996, JMS 2000)Kisiel et al. (JCP 1996, JMS 2000)– Ground-state rotational constantsGround-state rotational constants

– Analysis of the vAnalysis of the v44=n excited states=n excited states

Johnson et al. (ACPD 2006): Johnson et al. (ACPD 2006): – Quantitative database at 0.1 cmQuantitative database at 0.1 cm-1-1 resolution resolution– High-resolution spectraHigh-resolution spectra

T. Ford (JMS 1975)T. Ford (JMS 1975)– IR and Raman spectra of CHIR and Raman spectra of CH22II22 (and deuterated) (and deuterated)

– ““the the 11 band of CH band of CH22II22 in the vapor phase has in the vapor phase has

negligible intensity”negligible intensity”

3. Experimental3. Experimental

Bruker IFS 120 HR Fourier spectrometerBruker IFS 120 HR Fourier spectrometer

Spectral resolution 0.002 cmSpectral resolution 0.002 cm-1-1

Pyrex cell, path 300 cm, CaFPyrex cell, path 300 cm, CaF22 windows windows

CHCH22II22 at saturated vapour pressure at saturated vapour pressure

Spectral range 2250-3400 cmSpectral range 2250-3400 cm-1-1

Working in the dark to avoid photolysisWorking in the dark to avoid photolysis

15 hours integration 15 hours integration

4. Results4. Results

2970 2980 2990 3000 3010 3020 3030 3040 3050 3060 3070 3080 3090 3100 3110 31200.2

0.4

0.6

0.8

1.0

wavenumber in cm-1

inte

nsity

in a

.u.

1 6

4. Results4. Results

v4" =

0 1 2 3 4

4. Results4. Results

Q branches with Ka’ = 1 2 3 4 5 6 7 8 9 10 11

4. Results4. Results

v4" =

0 1 2 3 4

4. Results4. Results

From Johnson et al. (ACPD 2006)From Johnson et al. (ACPD 2006)

4. Results4. Results

4. Results4. Results

1 2 3 4 5 6-0,5

0,0

0,5

1,0

1,5

2,0

2,5 observed linear fit

-ln

(Q

bra

nch

su

rfa

ce)

v4 + 1

Lower state’s energy in cm-1

4. Results4. Results

Q branch positions in cm-1

4. Results4. Results

Band centers in cm-1

4. Results4. Results

Rotational constants A in cm-1

4. Results4. Results

Vibration-rotation interaction in cm-1

Future studiesFuture studies

« Global » fit of the « Global » fit of the 11 and and 66 bands and all bands and all

the « hot bands » with the « hot bands » with 44 excitation excitation

New spectra with a cw DFG laser (LISA)New spectra with a cw DFG laser (LISA)

Absorption spectra in a cold jet Absorption spectra in a cold jet

AcknowledgementsAcknowledgements

T. J. Johnson, T. A. Blake, A. Masiello T. J. Johnson, T. A. Blake, A. Masiello (PNNL Battelle)(PNNL Battelle)