Argon E 1Chloro12Difluoroethylene Complex Mark D Marshall Helen O Leung Hannah Tandon Joseph Messenger and Eli Mlaver Department of Chemistry Amherst College Supported by the National Science Foundation ID: 213574
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Slide1
Microwave Spectrum and Molecular Structure of the Argon-(E )-1-Chloro-1,2-Difluoroethylene Complex
Mark D. Marshall , Helen O. Leung, Hannah Tandon,Joseph Messenger, and Eli MlaverDepartment of Chemistry Amherst College
Supported by the National Science FoundationSlide2
Fluoroethylene-Argon ComplexesAs noted by Kisiel, Fowler, and
Legon, J. Chem. Phys. 95, 2283 (1991)Argon binds in either XCCF or FCF “cavity”Maximizing number of contacts with preferably heavy atoms
3.46 Å
3.55 Å
3.55 Å
F
F
Ar
3.47 Å
3.47 Å
F
F
F
Ar
3.53 Å
3.45 Å
Fine balance between dispersion and hard sphere repulsion
Nearly constant
Ar
–F distance
Argon provides
structureless
probe of electron density away from ethylene planeSlide3
Extension to FluorochloroethylenesOur results show that trends continueAr-vinyl chlorideAr-(Z)-1-chloro-2-fluoroethylene
Ar-2-chloro-1,1-difluoroethyleneAll non-planarAr-vinyl chloride exhibits tunneling motionSlide4
Argon-(E )-1-chloro-1,2-difluoroethyleneRelaxed potential scan
Gaussian 09MP2/6-311++G(2d,2p)Scan , optimize R
,
θ
R
Φ
x
y
zSlide5
Optimized
Ab Initio Structure
3.476 Å
3.979 Å
3.665 Å
71.2˚
Top view
Side view
A
= 1971 MHz
B
= 1229 MHz
C
= 894 MHz
a
= 0.40 D
b
= 0.81 D
c = 1.48 DSlide6
Chirped Pulse ExperimentStudied in the 6.0 – 18.0 GHz region with a CP-FTMW spectrometerAr-35ClFCCHF
Ar-37ClFCCHF1% ClFCCHF in Ar at 2 atm through 0.8 mm pulsed nozzle
Spectra obtained as 1.5 GHz portions, 20 W power, 4
s chirp
Ten 10-s FIDs per gas pulse
624,000 to 732,000 FIDs averaged
200 kHz FWHMSlide7
Narrow Band ExperimentLines re-measured and additional ones found in the 5.0 – 22.0 GHz region with a Balle-Flygare cavity FTMW spectrometer
Ar-35ClF13CCHF1% ClFCCHF in Ar at 2
atm
through 0.8 mm pulsed nozzle
0.5 MHz BW
Nozzle is mounted parallel to the resonator axis
Each spectral line is Doppler doubled
7 – 10
kHz FWHMSlide8
Typical Ar–
35
ClFCCHF Spectrum
c
- type
4
22
– 3
12
b
- type
6
16
– 5
05
672,000 FIDsSlide9
Spectroscopic ConstantsAr-CHFCF
35ClAr-CHFCF37Cl
Ar-CHF
13
CF
35
Cl
A/ MHz
1994.00824(70)
1949.6941(15)
1993.8597(13)
B/ MHz
1218.15445(32
)
1211.3922(20)
1215.3354(10)
C/ MHz
883.87197(43)
872.1060(39
)
882.4404(35)
J/ 10-3 MHz 4.7578(80
) 3.97(15)
2.30(18)K/
10-3 MHz –207.32(11
)
–194.34(51)
–205.02(64)
JK/ 10
-3 MHz
211.947(58)
200.15(49)
214.28(66)
J/ 10-3 MHz
1.6319(34)
1.446(56)
2.584(84)
K/ 10-3 MHz
121.752(93)
113.66(56
) 112.90(25)|aa| / MHz 37.0826(38) 29.2203(47)
37.185(16)|bb| /MHz –67.7729(37) –53.6415(52) –67.818(12)
|cc| / MHz 30.6903(37) 24.4212(47) 30.6324(80)
|bc| / MHz 26.95(31) 20.50(30) 26.05(33)No. of rotational transitions
8016
12No. of a type
201
0No. of b type
285
0
No. of c type321012No. of hyperfine components362
9342J range2 - 62 - 51 - 5
Ka range0 - 41 - 40 - 3rms / kHz
7.18 5.23 6.09
Watson A-reducedIr representationAABSSPFIT4 Sextic CD constants requiredFor Ar-CHFCF35
Cl:|ab|= 1.72(27) MHz|ac| = 7.3(34) MHzA
= 1971 MHzB = 1229 MHzC = 894 MHzAb initio predictionsSlide10
Ar (Extreme) Substitution Coordinates
|a
| /
Å
0.091(17)
|
b
| /
Å
1.1916(12)
|
c
| /
Å
3.35069(45)
Structures above and below plane are equivalent
Four possible argon locations
All are consistent with rotation of
quadrupole
tensor
In principal axis system of monomer:Slide11
Cl substitution strongly suggests one possibility
aCl / Å
b
Cl
/ Å
c
Cl
/ Å
1
0.9973
–1.6445
–0.3527
2
1.2494
1.6283
–0.2503
3
1.0599
1.7084
–0.2396
4
0.8078
–1.6921
–0.3634
Exp.
±1.0229(14)
±1.69364(89)
±
0.3098(48
)
13
C
isotopologues
provide additional confirmation
Use four possibilities to predict coordinates of
Cl
in principal axis system of
dimer
Substitution coordinates of
37
Cl strongly suggests #3
Also consistent with
ab
initio
predictionSlide12
13C substitution confirms this choice
aCl / Å
b
Cl
/ Å
c
Cl
/ Å
1
1.0804
0.0011
0.0628
2
0.9808
0.0053
0.1757
3
0.9768
0.0628
0.1759
4
1.0765
–0.0692
0.0626
Exp.
±0.9692(15)
Unphysical
±
0.1641(91
)
Use four possibilities to predict coordinates of
C1 in principal axis system of
dimer
Substitution coordinates of
13
C1 also indicates #3Slide13
Experimental Structure
Fix haloethylene at monomer geometryVary argon positionFit to 3 moments of inertia for
35
Cl and
37
Cl complexes using
Kisiel’s
STRFIT (
13C data too recent)
rms
= 0.091 amu Å
2Ar
locates in FCCl
cavity.Difference between
Ar–F and Ar–Cl
distances exceeds difference in
vdW radii.Slide14
Comparison with Fluoroethylene Complexes
3.58 Å
3.56
Å
Kisiel
, Fowler, and
Legon
,
J. Chem. Phys.
95,
2283 (1991)Slide15
Comparison with Chloroethylene Complexes
Distance from argon to center of C=C bond decreases with increasing halogen substitution
C1–Ar distance may be more consistent than
Ar
–F distance
Argon prefers to locate closer to fluorine atoms, that side of plane tilts toward
Ar
3.52 Å
3.59 Å
3.58 ÅSlide16
SummaryThe rotational spectra of three isotopologues of Ar–ClFCCHF have been observed and analyzed.Ar
–ClFCCHF has a non-planar structure, with binding most likely in the ClCF cavity to maximize contacts with heavy atoms as suggested by Kisiel, Fowler and Legon.Ar-F distance is shorter than the consistent 3.5 Å seen in previous species, further increasing the
Ar-Cl
distance over the difference in van
der
Waals radii.
Ar-C1 distance, however, is a consistent 3.5 – 3.6 Å Slide17
Modifications to Amherst CP-FTMW InstrumentBandwidth limited to 5 GHz
25 W power amplifierTektronix DPO72004C scope100 Gs s–1, 20 GHz analog BW
Direct detection of FID
250 MB fast memory
Only transfer summary frame
Rb
10 MHz standard
10 MHz crystal oscillator