Fourier–transform microwave and
millimeter–wave spectroscopy of
CH 2 IBr (v = 0)
Stéphane Bailleux
stephane.bailleux@univ-lille1.fr
University of Lille
June 17, 2014 – 69th ISMS Meeting
Spec tr oscopy of C H 2 X Y s pec ies

X , Y = { F, Cl, Br } : extensive studies

X = I
CH2I2 : Z. K i s i e l et al . (1996)
CH2IF : C. Puzzarini et al. (2011)
CH2ICl : S. Bailleux et al. (2011)
CH2IBr : this work
Atmospheric chemistry of iodine
A. Saiz–Lopez et al.
Chem. Review. 2011
Aerosol
OIO
I, I2, IO, IO2:
detected
IX
IO
- – – ℎn
O3 loss
I2, CH2I2, CH2IX, CH3I, …
I
Sourc e of atmos pher ic iodine
S. Archer et al.
J. Geophys. Res. 2006
CH2 IBr : 5%
CH3 I
23%
C2H5 I : 6%
CH2 ICl
CH2 I2
22%
44%
di-halogenated
species are much
more photolabile
C o n g e s te d rotational spectra !
 Complex hyperfine structure (quadrupole):
IBr = 3/2
⇒ 24 hyperfine levels
I I = 5/2
 quadrupolar and rotational constants : similar magnitudes
 small rotational constants and low frequency ICBr
bending vibrational mode
 2 Br isotopologues :
79Br
: 81Br = 1 : 1
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
b
 Dipole moments (D)
µa = 0.09
µb = 1.54
a
data not available in the literature
Cs symetry
k = -0.998
Predicted microwave spectra (b–type)
search candidates
MHz
Predicted microwave spectra
23000
23500
24000
24500
25000
25500
26000
Predicted microwave spectra
low N,
Q-branch
transitions
23000
23500
24000
111-000
24500
25000
25500
26000
1 11 – 0 00 transition assigned
Predicted (B3LYP)
Observed
111 – 000 transition after fitting
A, B, C
and
N.Q.C.C. determined
As s ignments of Q - br anches
C H 2I 79B r
C H 2I 81B r
Ex amples of s pec tr a
CH 2 I
81
Br
N K a K c = 111 – 0 00
F 1 = J + I Br
F1 = F1 + I I
Results
assigned (J  132 Ka  14)
µw ( 23 – 25 GHz) : µb
mmw (120 – 243 GHz) : µa
mmw (200 – 243 GHz): µb
79Br
81Br
428 439
009 0021
0441 0519
Constants (MHz) of CH 2 I 79 Br
observed
Rotation
A
B
C
Iodine Coupling
caa
cbb
|cab|
MP2 6–311+G
r0 structure
0024054.8910
0000892.3920
0000865.0090
26687
00895
00867
electronic structure
–1275.31
00236.38
01296.20
–1300
00263
01278
0304.38
00+4.35
0418.01
00315
000–7
00414
Bromine Coupling
caa
cbb
|cab|
Geometry
CH2IF
re
CH2ICl
r0
CH2I79Br
r0
CH2I2
rz
C – I /Å
2.1410
2.1485
2.1434
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
2.134(2)
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
Contributors
Measurement & analysis
 Toho University (MMW)
K. Taniguchi
Computations
 Kean University
W. Bailey
S. Sakai
H. Ozeki
 Shizuoka University (FTMW)
T. Okabayashi
 acknowledgements
French National Research Agency
 Lille University
D. Duflot
Centrifugal distortion of CH 2 I 79 Br
quartic (kHz)
DJK
DJK
DKJ
103  d1 20000000
103  d2 20000000
observed
MP2 SDB-VTZ
000.1336491 (37)
–8.82364 (11)0
374.083 (12) 0001
–7.12740 (55) 0
–0.09268 (24) 0
0.123
–8.6100
374. 0001
–6.4300 0
–0.0753
sextic (mHz)
HJK
000.03082 (13)
HJK
001.027 (11)00
HKJ
0–544.3 (16) 00000
HKJ
20008. (204) 00000
103  h1 20000000
04.567 (32)
103  h2 20000000
00.146 (25)
103  h3 20000000 00000.01155 fixed
00.0283
000.71300
0–498.0000000
19700.000000
3.9800
00.126
000.0105
0
Quadrupolar tensors of CH 2 I
79Br
cxx
cyy
czz
79 Br
I
/ MHz
–289.7496 (49)
981.0133 (39)
/ MHz
–308.7330 (17)
1038.9290 (18)
/ MHz
598.4826 (49)
–2019.9423 (39)
h
0.03170
0.0287
qza / °Hz
35.13000
29.88000
Millimeter-wave spectrometer (Toho)