CAMERON M FUNDERBURK SYDNEY A GASTER TIFFANY R TAYLOR GORDON G BROWN Department of Science and Mathematics Coker College Hartsville SC TH05 Spectroscopists Microwave Spectroscopists ID: 626813
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Slide1
MEASURING CONFORMATIONAL ENERGY DIFFERENCES USING PULSED-JET MICROWAVE SPECTROSCOPY
CAMERON M FUNDERBURK
, SYDNEY A GASTER,
TIFFANY R TAYLOR
, GORDON G
BROWN
Department of Science and Mathematics
Coker College
Hartsville, SC
TH05Slide2
SpectroscopistsSlide3
Microwave Spectroscopists
Frequency
Narrow line-width
Small Error
Intensity
Question: Can we use experimental intensities more effectively?Slide4
Conformational Energy Differences
pre-
Balle
/Flygare
1
pulsed jet cavity
s
tatic cell w/ accurate relative intensitiesexperimental energy differences often reported
1
Balle, T.J.,
Flygare
, W.H.,
Rev. Sci.
Instrum
. 1981,
52
(1), 33–45.Slide5
Conformational Energy Differences
post
Balle
/Flygare
1
pulsed jet (and rise of computing power)
cooling in pulsed jet
use of a cavity – relative intensities not accurateexperimental relative intensities seldom reported
1
Balle, T.J.,
Flygare
, W.H.,
Rev. Sci.
Instrum
. 1981,
52
(1), 33–45.Slide6
Conformational Energy Differences
Chirped-pulse microwave spectroscopy
provides accurate relative intensities
2
do relative intensities agree with energy differences between conformers?
2
Gordon G. Brown, Brian C. Dian, Kevin O. Douglass, Scott M. Geyer, Steven T. Shipman, and Brooks H. Pate,
Rev. Sci.
Instrum
.
79
(2008) 053103.Slide7
Hypothesis:
R
elative
intensities
are
proportional to the conformer populations present before the expansion
occurs (if we use He gas).
We can use relative intensities to measure experimental relative energies between conformers.Slide8
Example: Ethylperoxyl radical
intermediate in ethanol combustion
two conformers,
gauche
and
trans
conformation energies determine
most likely reaction path
reaction kineticsSlide9
Relaxation of conformers in pulsed valves3
3
R.S.
Ruoff
, T.D.
Klots
, T.
Emilsson
, and H.S.
Gutowsky
,
J. Chem. Phys
.
93
, (1990) 3142-3150.Slide10
Relaxation of conformers in pulsed valves3
“
When helium was used
as the carrier gas all of the conformers showed
little if any
e
vidence of conformer relaxation
…
That is,
the signal intensities were consistent with the equilibrium ratio
of concentrations (
K
eq
) predicted be the energy difference (
Δ
E) between conformers at T~298K,
K
eq
= f
exp
(-
Δ
E/RT)
”
1
f = ratio of numbers of equivalent forms (e.g. 2 gauche vs. 1 trans)
3
R.S.
Ruoff
, T.D.
Klots
, T.
Emilsson
, and H.S.
Gutowsky
,
J. Chem. Phys
.
93
, (1990) 3142-3150.Slide11
Relaxation of conformers in pulsed valves3
3
R.S.
Ruoff
, T.D.
Klots
, T.
Emilsson
, and H.S.
Gutowsky
,
J. Chem. Phys
.
93
, (1990) 3142-3150.Slide12
Coker College CP-FTMW Spectrometer4
4
Miranda Smith, Brandon D. Short, April M. Ruthven, K. Michelle Thomas, Michael J. Hang, Gordon G. Brown,
J. Mol.
Spectr
.,
307
, (2015) 49-53.Slide13
Coker College CP-FTMW SpectrometerSlide14
Target Molecules
propanal
cis
gauche
3
R.S.
Ruoff
, T.D.
Klots
, T.
Emilsson
, and H.S.
Gutowsky
,
J. Chem. Phys
.
93
, (1990) 3142-3150.Slide15
Intensity Ratio Predictions
ethyl
formate
(gauche/trans)
propanal
(gauche/cis)
predicted equilibrium
ratio in valve (T = 296K)
1.63
0.43
predicted
transition
intensities
in jet (1K)
0.86
0.52
Instrument
response
2.0
1.5
overall
predicted intensity ratio
2.8
0.34Slide16
Preliminary experiments:ethyl
formate
trans
10962 MHz
gauche
14059 MHz
ratio (g/t)
1
21.36
3.84
0.18
2
23.26
3.62
0.16
3
28.84
2.41
0.08
4
23.64
3.22
0.14
5
21.48
3.94
0.18
6
21.63
3.77
0.17
7
25.85
4.75
0.18
8
27.13
2.42
0.09
9
25.92
3.57
0.14
10
26.21
3.38
0.13
avg
24.53
3.49
0.15
std
dev
2.62
0.700.04
Experiment 1
:
transition: 2
02
– 1
01
each trial: 100
avgs
Predicted
ratio =
2.8
Expt. 1 ratio =
0.15
set carrier frequency to
ν
– 200 MHz
(10762 MHz and
13859 MHz)Slide17
Preliminary experiments:ethyl
formate
trans
10962 MHz
gauche
14059 MHz
ratio (g/t)
1
8.83
4.42
0.50
2
9.15
4.29
0.47
3
8.84
4.42
0.50
4
8.72
4.44
0.51
5
9.53
4.53
0.48
6
9.18
4.57
0.50
7
9.75
4.73
0.48
8
10.19
4.75
0.47
9
9.36
4.74
0.51
10
10.35
4.99
0.48
avg
9.39
4.59
0.49
std dev
0.57
0.21
0.02Experiment 2:repeat Experiment 1 on different daytransition: 202 – 101 each trial: 100 avgsPredicted ratio = 2.8Expt. 1 ratio = 0.15Expt. 2 ratio = 0.49set carrier frequency to ν – 200 MHz(10762 MHz and 13859 MHz)Slide18
Preliminary experiments:ethyl
formate
trans
10962 MHz
gauche
14059 MHz
ratio (g/t)
1
8.16
6.47
0.79
2
8.04
6.30
0.78
3
7.65
6.76
0.88
4
8.42
6.31
0.75
5
8.20
6.52
0.79
6
7.75
6.29
0.81
7
8.66
6.22
0.72
8
7.94
6.51
0.82
9
8.18
6.50
0.79
10
8.34
6.51
0.78
avg
8.13
6.44
0.79
std dev
0.30
0.16
0.04Experiment 3:repeat Experiment 2 on same day with different carrier frequenciestransition: 202 – 101 each trial: 100 avgsPredicted ratio = 2.8Expt. 1 ratio = 0.15Expt. 2 ratio = 0.49Expt. 3 ratio = 0.79set carrier frequency to ν – 300 MHz(10662 MHz and 13759 MHz)Slide19
Preliminary experiments:ethyl
formate
Further Experiments
:
transition: 2
02
– 1
01
Predicted ratio =
2.8
Experiment
trans
10962 MHz
gauche
14059 MHz
ratio (g/t)
1
24.53
3.49
0.15
2
9.39
4.59
0.49
3
8.13
6.44
0.79
4
7.45
1.12
0.15
5
19.09
3.42
0.18
6
17.89
2.99
0.17
7
17.06
3.13
0.18
8
17.02
2.94
0.17
9
12.65
3.51
0.28
10
12.253.440.281119.472.450.13
12
7.66
5.48
0.71
13
4.20
1.08
0.26
14
11.70
3.08
0.26
15
11.00
3.34
0.30
16
11.42
3.14
0.27
avg
13.18
3.35
0.30
std
dev
5.48
1.34
0.20Slide20
Preliminary experiments:propanal
cis
10493 MHz
gauche
8463 MHz
ratio (g/t)
1
2.51
0.086
0.034
2
2.63
0.084
0.032
3
2.41
0.090
0.037
4
2.432
0.094
0.039
5
2.386
0.096
0.040
6
2.394
0.092
0.039
7
3.981
0.100
0.025
8
3.492
0.100
0.029
9
2.372
0.105
0.044
10
2.59
0.112
0.043
avg
2.720
0.096
0.036
std
dev
0.555
0.009
0.006Experiment 1:transition: 101 – 000 each trial: 500 avgsPredicted ratio = 0.34Expt. 1 ratio = 0.036set carrier frequency to 10000 MHz and8000 MHzRoom Temp (296K)Slide21
Preliminary experiments:propanal
cis
10493 MHz
gauche
8463 MHz
ratio (g/t)
1
2.211
0.1889
0.085
2
2.142
0.1842
0.086
3
2.228
0.1912
0.086
4
2.347
0.1965
0.084
5
2.348
0.1758
0.075
6
2.567
0.1789
0.070
7
2.443
0.1968
0.081
8
2.445
0.1911
0.078
9
2.47
0.1779
0.072
10
2.519
0.1897
0.075
avg
2.372
0.187
0.079
std
dev
0.142
0.008
0.006Experiment 2:transition: 101 – 000 each trial: 500 avgsPredicted ratio = 0.34 (296K)Expt. 1 ratio = 0.036 (296K)Predicted ratio = 0.44 (354K)Expt. 2 ratio = 0.079 (354K)set carrier frequency to 10000 MHz and8000 MHzHeated nozzle (354K)Slide22
Preliminary experiments:propanal
cis
10493 MHz
gauche
8463 MHz
ratio (g/t)
1
1.697
0.1093
0.064
2
1.709
0.1139
0.067
3
1.695
0.1219
0.072
4
1.597
0.1321
0.083
5
1.765
0.1361
0.077
6
1.658
0.1277
0.077
7
1.644
0.1268
0.077
8
1.71
0.1373
0.080
9
1.72
0.1524
0.089
10
1.618
0.1344
0.083
avg
1.681
0.129
0.077
std
dev
0.051
0.012
0.008Experiment 3:transition: 101 – 000 each trial: 500 avgsPredicted ratio = 0.34 (296K)Expt. 1 ratio = 0.036 (296K)Predicted ratio = 0.44 (354K)Expt. 2 ratio = 0.079 (354K)Expt. 3 ratio = 0.077 (296K)set carrier frequency to 10000 MHz and8000 MHzRoom Temp (296K)Slide23
Experimental consistency (?)
all experimental parameters same
valve timing
valve shims
backing pressure
same tank of chemical/He mix
microwave pulse powerSlide24
Conclusion
It is difficult to reproduce signal intensities with a pulsed jet.
We seem to observe conformer relaxation despite using helium as a carrier gas.
Future Work
Compare relative intensities
of conformer spectra, not individual transitions.Slide25
American Chemical Society – Petroleum Research Fund (
56530-UR6)
SCICU Student-Faculty Research Program
Coker College
25
AcknowledgementsSlide26Slide27
Preliminary experiments:isopropyl alcohol
Experiment date
trans
13254 MHz
gauche
13407 MHz
ratio (g/t)
3/14
0.64
1.30
2.03
3/15
0.43
1.15
2.67
3/15
0.91
1.39
1.53
avg
2.08
std
dev
0.57
Experiment 1
:
transition: 1
01
– 0
00
each experiment:
10 trials of 100
avgs
each
set carrier frequency to
13000 MHz – measured both transitions with same measurements