Transcript Barium Sulfide.pptx

Measurement of the Vibrational
Population Distribution of Barium
Sulfide, Seeded in an Argon Supersonic
Expansion, Following Production
Through the Reaction of Laser Ablated
Barium with Carbonyl Sulfide
Chris T. Dewberry, Garry S. Grubbs II,
Kerry C. Etchison and Stephen A. Cooke,
Department of Chemistry, University of
North Texas, Denton, TX, USA
Chirp Pulse Techniques
• The recent advancement in microwave spectroscopy of Chirped
Pulse Fourier Transform Microwavea,b,c (CP-FTMW) techniques
have greatly broadened search regions shortening acquisition
times while also allowing for relative correct intensities of spectra
a. G.G. Brown, B.C. Dian, K.O. Douglass, S.M. Geyer and B.H. Pate, J. Mol. Spec., 238, 200.
b. Brown et al, Rev. Sci. Instr., 79, 053103.
c. G.S. Grubbs II et al, J. Mol. Spec., 251, 378.
Laser Ablation Techniques
• Advancements in Laser Ablation Techniques, particularly the
Walker-Gerry Ablation Nozzlea (Pictured), allow for the
introduction of solid, transient, and plasma chemistry to be
studied in the gas phase by microwave spectrometers
a. K.A. Walker and M.C.L. Gerry, J. Mol. Spec., 182, 178.
Instruments
SACI-FTMW (upper left)
Balle-Flygare Type (above)
• The instruments used in these experiments were a
Search Accelerated, Correct Intensity Fourier Transform
Microwave (SACI-FTMW)a spectrometer with Laser
Ablation Source and a Balle-Flygare type FTMW
spectrometer with Laser Ablation Sourceb
a. G.S. Grubbs II, C.T. Dewberry, K.C. Etchison, K. Kerr, and S.A. Cooke, Rev. Sci. Instr., 78, 096106.
b. K.C. Etchison, C.T. Dewberry, and S.A. Cooke, Chem. Phys., 342, 71.
SACI-FTMW with Laser Ablation
•
•
Pictured above is a sampling of spectra from SACI-FTMW with Laser Ablation Sourcea
The relative intensities of the spectra demonstrate good agreement with isotopic abundance
a. G.S. Grubbs II, C.T. Dewberry, K.C. Etchison, K. Kerr, and S.A. Cooke, Rev. Sci. Instr., 78, 096106.
Barium Sulfide
• Given these advancements, new questions can
be asked about the chemistry of the molecule
in the laser ablation event
• These questions are more easily approached
using simple diatomic species
• Barium Sulfide, a previously studieda closed
shell molecule, seemed a good candidate for
these experiments due to its large dipole
moment
a. D. A. Helms, M. Winnewisser, and G. Winnewisser, J. Phys. Chem., 84 (1980), 1758
Barium and Sulphur Isotopes
Isotopes
Natural
Abundance (%)
Nuclear
Spin, I
130Ba
0.106
0
132Ba
0.101
0
Isotopes
Natural
Abundance (%)
Nuclear
Spin, I
32S
94.93
0
33S
0.76
3/2
134Ba
2.417
0
135Ba
6.592
3/2
34S
4.29
0
136Ba
7.854
0
36S
0.02
0
137Ba
11.232
3/2
138Ba
71.698
0
Barium Sulfide
• J = 2 – 1, ν = 0 transition of 138Ba32S to 136Ba32S
was 8.94 : 1 and the natural isotopic ratio is
9.12 : 1
• QUESTION: Is there a parameter we can
manipulate to alter the vibrational state
distribution intensities or is everything
dominated by the supersonic expansion?
Parameters Studied
•
•
•
•
•
Laser Power
Backing Gas Pressure
OCS Concentration
OCS in Argon and Helium
H2S in Argon and Helium
Variables held constant while not being studied: 75% Laser
Power, .3% OCS Concentration, Argon backing gas, 4.5 atm
backing pressure
Notes
• BaS was seen to be present simply by a test of
the Laser being on vs. off
• RELATIVE intensities have been used in the
experiments by as ratios of one transition to
another
• Any other transitions have been measured
with the Balle-Flygare type FTMW
spectrometer
• Experiments were performed on the 3 lowest
vibrational states of the main isotopologue
Experimental Control
• 20 gas units of OCS in Argon at 7000 gas units
(~4.5 atm) with a Laser Power of 75%
maximum power (1560 gas units = 1 atm)
• Chirp pulse lengths are 3 μs with a span of 2
GHz being examined at a time
• Timings are generally the same throughout
the experiment
BaS Spectra
• A sample BaS spectra taken from the SACIFTMW spectrometer (96508 Averaging Cycles)
Control Scan Zoom In 12100-12450 MHz
Control
BaS Run
Band Ratio
Intensity Ratio
Value
96508 Shots
ν=1/ν=0
2.57/15.9
0.162
J = 2-1
ν=2/ν=0
1.81/15.9
0.114
ν=3/ν=0
1.32/15.9
0.083
ν=4/ν=0
1.01/15.9
0.064
ν=5/ν=0
0.73/15.9
0.046
ν=6/ν=0
0.56/15.9
0.035
Laser Power Results
Laser Power
Band Ratio
Intensity Ratio
Value
Control
65%
ν=1/ν=0
2.434/16.782
0.145
0.162
ν=2/ν=0
1.857/16.782
0.111
0.114
ν=1/ν=0
6.851/32.666
0.210
0.162
ν=2/ν=0
5.564/32.666
0.170
0.114
ν=1/ν=0
3.504/17.022
0.206
0.162
ν=2/ν=0
2.864/17.022
0.168
0.114
ν=1/ν=0
1.841/7.033
0.262
0.162
ν=2/ν=0
1.456/7.033
0.207
0.114
ν=1/ν=0
0.648/2.351
0.276
0.162
ν=2/ν=0
0.576/2.351
0.245
0.114
75%
80%
85%
90%
Laser Power Conclusion
• A trend of the ν =1/ν=0 and ν =2/ν=0 ratios
show an increase toward the populations of
higher vibrational states as laser power
increases
• Tradeoff of intensity of the spectra with
alteration of the distribution
Backing Gas Pressure (with OCS)
Results
Pressure (Arb.
Units)
Band Ratio
Intensity Ratio
Value
Control
6718
ν=1/ν=0
4.330/21.721
0.199
0.162
ν=2/ν=0
3.583/21.721
0.165
0.114
ν=1/ν=0
4.157/20.620
0.202
0.162
ν=2/ν=0
3.235/20.620
0.157
0.114
ν=1/ν=0
2.375/11.642
0.204
0.162
ν=2/ν=0
1.921/11.642
0.165
0.114
ν=1/ν=0
0.861/4.60
0.187
0.162
ν=2/ν=0
0.530/4.60
0.115
0.114
ν=1/ν=0
0.702/3.36
0.209
0.162
ν=2/ν=0
0.5401/3.36
0.161
0.114
ν=1/ν=0
0.738/4.01
0.184
0.162
ν=2/ν=0
0.611/4.01
0.152
0.114
5720
4704
3709
2692
1707
Backing Gas Pressure (with OCS)
Conclusion
• Non-conclusive results due to inconsistent
trends in the data
• Higher backing pressures intensify the bands
(as expected with the chemistry in the jet)
Concentration of OCS Results
Concentration
Band Ratio
Intensity Ratio
Value
Control
.3%
ν=1/ν=0
0.729/4.58
0.164
0.162
ν=2/ν=0
0.560/4.58
0.122
0.114
ν=1/ν=0
0.979/6.16
0.159
0.162
ν=2/ν=0
0.739/6.16
0.120
0.114
ν=1/ν=0
No Signal
N/A
0.162
ν=2/ν=0
No Signal
N/A
0.114
.6%
.9%
Concentration of OCS Conclusion
• No observed concentration dependence for
the vibrational state distribution
• There is a point at which the mixture becomes
too rich causing BaS signal elimination
OCS in Argon and Helium Result
Backing Gas
Band Ratio
Intensity Ratio
Value
Control
Argon
ν=1/ν=0
3.085/14.518
0.212
0.162
ν=2/ν=0
2.131/14.518
0.147
0.114
ν=1/ν=0
0.935/6.267
0.149
0.162
ν=2/ν=0
0.742/6.267
0.118
0.114
Helium
OCS in Argon and Helium Conclusion
• As expected, the Helium lowered the intensity
of the ν = 0 transition due to a warmer
rotational temperature
• No real change to the vibrational state
populations due to Argon or Helium with OCS
Barium Sulfide Synthesis
Ba + OCS
BaS + CO
Done in an Oven
Winnewisser*
Ba + OCS
BaS + ___
Laser Ablation
Ba + Scontaining gas
BaS + ___
Parameter
*D. A. Helms, M. Winnewisser, and G. Winnewisser, J. Phys. Chem., 84, 1758.
H2S Gas Mixture Results
Backing Gas
Band Ratio
Intensity Ratio
Value
Control
Argon
ν=1/ν=0
0.788/3.805
0.207
0.162
ν=2/ν=0
0.397/3.805
0.104
0.114
ν=1/ν=0
No Signal/.771
N/A
0.162
ν=2/ν=0
No Signal/.771
N/A
0.114
Helium
OCS Gas Mixture Results
Backing Gas
Band Ratio
Intensity Ratio
Value
Control
Argon
ν=1/ν=0
3.085/14.518
0.212
0.162
ν=2/ν=0
2.131/14.518
0.147
0.114
ν=1/ν=0
0.935/6.267
0.149
0.162
ν=2/ν=0
0.742/6.267
0.118
0.114
Helium
H2S Gas Mixture Conclusion
• There is a change of the population
distribution not seen in the previous
experiments (ν=1/ν=0 ratio goes up while the
ν=2/ν=0 ratio relatively remains the same)
• H2S mixed with Helium is not strong enough to
be detected currently
Vibrational State Testing
• Laser power had a trend of increasing the ratios
of ν=1/ν=0 and ν=2/ν=0, but with a signal
intensity tradeoff
• Backing pressures were non-conclusive
• Mixtures of OCS in Argon and Helium only
provided knowledge currently understood by the
supersonic expansion
• H2S mixtures in Argon yielded an increase in one
vibrational state ratio, ν=1/ν=0, while leaving the
ν=2/ν=0 ratio relatively unchanged while signal
issues prevented the Helium mixed analog to be
studied further
Measured Transitions
Isotopomer
138
32
Ba S
ν
J’ - J’’
Frequency
(MHz)
0
1-0
2-1
3-2
4-3
1-0
6185.108
12370.194
18555.236
24740.207
6166.163
2-1
12332.301
4
3-2
2-1
3-2
2-1
3-2
2-1
18498.397
12294.305
18441.404
12256.203
18384.248
12217.991
5
6
7
0
3 -2
2-1
2-1
2-1
2-1
18384.248
12179.666
12141.227
12102.669
12388.006
12384.321
12387.169
1
2
3
137
32
Ba S
3-2
18581.170
18578.776
18575.922
Isotopomer
136
32
Ba S
ν
J’ - J’’
0
1-0
2-1
3-2
2-1
3-2
2-1
2-1
2-1
1
135
32
Ba S
2
3
0
3-2
134
138
32
Ba S
34
Ba S
1
2-1
0
2-1
3-2
2-1
2-1
3-2
2-1
1
0
1
Frequency
(MHz)
6202.231
12404.438
18606.602
12366.387
18549.526
12328.235
12289.972
12422.457
12416.185
12426.926
18633.120
18631.563
12377.540
12378.359
12439.697
18659.488
12401.487
11780.667
17670.952
11745.456
This listing is all measured transitions to date including transitions only observed by the cavity
experiment. High resolution of the transitions are due to the cavity experiment.
Rotational Constants
Our Work for 138Ba32S
G. Winnewissera for 138Ba32S
Constants
Frequency (MHz)
Constants
Frequency (MHz)
Y01
3097.28318(674)
Y01
3097.28216(26)
Y02
-0.000918966(198)
Y02
-0.000918568(63)
Y03
0.000000000033(32)
Y03
NOT REPORTED
Y11
-9.448321(323)
Y11
-9.44620(33)
Y21
-0.012240(113)
Y21
-0.013323(66)
Y31
-0.0001314(105)
Y31
NOT REPORTED
Y12
-0.000001017(234)
Y12
-0.000001554(73)
Y22
-0.0000001956(873)
Y22
NOT REPORTED
Δ01
-3.257(559)
ΔBa
01
NOT REPORTED
S
Δ01
-5.1045(780)
S
Δ01
NOT REPORTED
Ba
• Hyperfine structure observed for 135Ba and 137Ba
species
a. D. A. Helms, M. Winnewisser, and G. Winnewisser, J. Phys. Chem., 84, 1758
Overall Conclusions
• Laser Power and H2S gas mixtures shifted the
distribution of the vibrational band ratio for
populations suggesting different chemistry is
happening in the ablation process for the
molecule
• Many vibrational state transitions have been
studied for isotopologues of the BaS molecule
and rotational constants as well as BornOppenheimer Breakdown terms have been
determined and reported
Acknowledgements
• Funding from NSF
• The Cooke Group
Future Work
• Nozzle Design
• Other Backing Gases (Ne, He/Ne, Xe, etc.)
• Other Gases containing Sulphur (CS2)
Balle-Flygare Spectrometer Techniques
• Balle-Flygare Fourier Transform Microwave1 (FTMW)
spectrometer advancements of coaxial orientation
of the sample nozzle2 allows for increased resolution
of measured spectra ( ~7 kHz linewidths).
Overview
•
•
•
•
•
Techniques in Microwave Spectroscopy
Dynamics of the Ablation Process Experiments
Measured Transitions
Rotational Constants
Overall Conclusions