1. Stéphane Bailleux stephane.bailleux@univ-lille1.fr University of Lille
Fourier–transform microwave and millimeter–wave spectroscopy of CH2IBr (v = 0)
Stéphane Bailleux
University of Lille
June 17, 2014　– 69th ISMS Meeting

2. Spectroscopy of CH2 XY species
X , Y = { F, Cl, Br } : extensive studies
X = I
CH2I2 : Z. Kisiel et al. (1996)
CH2IF : C. Puzzarini et al. (2011)
CH2ICl : S. Bailleux et al. (2011)
CH2IBr : this work

3. Atmospheric chemistry of iodine
A. Saiz–Lopez et al.
Chem. Review
Aerosol I IO
OIO IX
I2, CH2I2, CH2IX, CH3I, …
I, I2, IO, IO2:
detected
O3 loss
-–– ℎn

4. Source of atmospheric iodine
S. Archer et al.
J. Geophys. Res
CH2 ICl
44%
CH2 I2
22%
CH3 I
23%
CH2 IBr : 5%
C2H5 I : 6%
di-halogenated
species are much
more photolabile

5. Congested rotational spectra !
Complex hyperfine structure (quadrupole):
quadrupolar and rotational constants : similar magnitudes
small rotational constants and low frequency ICBr bending vibrational mode
2 Br isotopologues : 79Br : 81Br = 1 : 1
IBr = 3/2
⇒ 24 hyperfine levels
I I = 5/2

6. High level quantum chemical calculations
Rotational constants (MP2)
Centrifugal distortion constants, up to sextic (B3LYP)
Quadrupolar coupling constants cij (a = I, Br)
cij (a) = eQa /h qij(a)
HeQq(a) = - ⅙ QI, Br : ∇EI, Br
Dipole moments (D)
µa = 0.09
µb = 1.54 b a
Cs symetry
k =
data not available in the literature

7. Predicted microwave spectra (b–type)
search candidates
MHz

8. Predicted microwave spectra
23000
23500
24000
24500
25000
25500
26000

9. Predicted microwave spectra
23000
23500
24000
24500
25000
25500
26000
low N,
Q-branch
transitions

10. 111 – 000 transition assigned
Predicted (B3LYP)
Observed

11. 111 – 000 transition after fitting
A, B, C and N.Q.C.C. determined

12. Assignments of Q-branches
CH2I79Br
CH2I81Br

13. Examples of spectra NKaKc = 111 – 000 F1 = J + IBr F1 = F1 + I I
CH2I81Br

14. 79Br 81Br Results assigned (J  132 Ka  14) µw ( 23 – 25 GHz) : µb
428
439
mmw (120 – 243 GHz) : µa
009
0021
mmw (200 – 243 GHz): µb
0441
0519

15. Constants (MHz) of CH2 I 79Br
observed
MP2 6–311+G
Rotation A
26687 B
00895 C
00867
Iodine Coupling
caa –
–1300
cbb
00263
|cab|
01278
Bromine Coupling
00315
000–7
00414
r0 structure
electronic structure

16. Geometry HCH / ° ICX / ° XCH / ° CH2IF CH2ICl CH2I79Br CH2I2 re r0 rz
C – I / Å
2.1410
2.1485
2.1434
2.134(2)
C – X / Å
1.3584
1.7541
1.9147
C – H / Å
1.0841
1.0832
1.0817fixed
1.085
HCH / °
112.45
107.93
107.86
111.27
ICX / °
110.79
113.03
113.47
114.0(3)
XCH / °
109.95
112.16
111.80

17. Concluding remarks Organic iodine in the atmosphere:
ozone depletion
impact on the radiative balance
our data (hopefully) …
will prompt vibrational spectroscopic studies
give the potential for atmospheric monitoring

18. Measurement & analysis
Contributors
Measurement & analysis
Computations
Toho University (MMW)
K. Taniguchi
S. Sakai
H. Ozeki
Shizuoka University (FTMW)
T. Okabayashi
Kean University
W. Bailey
Lille University
D. Duflot
acknowledgements
French National Research Agency

19. Centrifugal distortion of CH2 I 79Br
observed
MP2 SDB-VTZ
quartic (kHz)
DJK
(37)
0.123
– (11)0
–8.6100
DKJ
(12) 0001
103  d
– (55) 0 –
103  d
– (24) 0
–0.0753
sextic (mHz)
HJK
(13)
(11)00
HKJ
0–544.3 (16) 00000 0–
(204) 00000
103  h
(32)
103  h
(25)
00.126
103  h
fixed

20. Quadrupolar tensors of CH2 I 79Br
cxx / MHz
– (49)
(39)
cyy / MHz
– (17)
(18)
czz / MHz
(49)
– (39) h
0.0287
qza / °Hz

21. Millimeter-wave spectrometer (Toho)