Analysis of the far IR spectrum of
trimethylene sulfide using
evolutionary algorithms
Jennifer van Wijngaarden, Durell Desmond, Aimee Bell
Department of Chemistry, University of Manitoba, Winnipeg, Canada
W. Leo Meerts
Radboud University, Nijmegen, Netherlands
Trimethylene Sulfide
 Ring inversion tunneling
 Ground and first excited vibrational
state (ring puckering) are doubled
 MW spectrum exhibits tunneling
splitting
D. O. Harris, H. W. Harrington, A. C. Luntz and W. D. Gwinn,
J. Chem. Phys. 44, 3467 (1966).
2
MW spectrum of TMS


D. O. Harris, H. W. Harrington, A. C. Luntz and W. D. Gwinn,
J. Chem. Phys. 44, 3467 (1966).
3
12 a-type and 3 c-type transitions reported
Evidence of perturbation
Our MW spectrum of TMS… in progress


11112
11112.2
11112.4
11112.6
11112.8
101-000 pure rotational transitions
Tunneling splitting ~7.5 MHz
11113
11113.2
Frequency/MHz
4
11113.4
11119.4 11119.6 11119.8
11120
11120.2 11120.4 11120.6 11120.8
Frequency/MHz
Canadian Light Source
5
Photo courtesy of Canadian Light Source Inc.
FTIR Spectrometer
at the Far IR beamline
Resolution ~0.00096 cm
Bruker IFS125HR
6
Photo courtesy of Canadian Light Source Inc.
Far IR spectroscopy at the CLS
 2 m multipass cell
 80 m absorption
 Pressure: 85-950 mTorr
 Temperature: 250 K, 298 K
Series of experiments to cover:
 Range: 50-1050 cm-1
 Resolution: 0.00096 cm-1
2 m multipass cell
7
Ring puckering vibration and hotbands
12 cm-1 tunneling splitting
cm-1
8
Looking for patterns…
Q branch 139 cm-1
)
P branch of higher
tunneling state
)
R branch of lower
tunneling state
Q branch 151 cm-1
9
G03 DFT B-3LYP/6-311G++(2d,2p)
Higher bands
530 cm-1
845cm-1
500
cm-1
1000
10
845 cm-1 bands

Tunneling splitting ~1.4 cm-1

Two a-type rovibrational bands

11
Should also have c-type
rovibration-inversion bands

~1000 lines assigned

Evidence of perturbation
530 cm-1 bands

Tunneling splitting ~0.03 cm-1

Two a-type rovibrational bands

Should also have c-type rovibrationinversion bands

Prototype band for analysis using
evolutionary algorithms


Need preliminary analysis
Assigned ~2300 lines using LW plots
8<J<59
0<Ka<10
12
R-branch Loomis-Wood plot
530 cm-1 band
13
P-branch Loomis-Wood plot
530 cm-1 band
14
Evolutionary Algorithm (EA) Approach
W. L. Meerts and M. Schmitt, Int. Rev. Phys. Chem. 25, 353 (2006).

Goal: (More) Automated spectral assignment

Genetic algorithms based on natural selection
processes

pyrazine
Nicolet 5700, resolution ~0.09 cm-1
Applied as a global optimizer to analyze spectra

Covariance Matrix Adaption- Evolutionary Strategy
(CMA-ES) algorithm

Has been successfully applied to NMR, LIF, UV
absorption spectra etc.

Used for FTIR spectrum of pyrazine
M. Schmitt et al., J. Mol. Spectrosc. 57, 74 (2009).
15
EA method applied to TMS





Starting parameters

Taken from preliminary assignment via LW plot
Prepare spectra


Remove Q branch, hotband Q branches, water lines
Smooth background
Preliminary tests


Gauge sensitivity of parameters, test convergence etc.
Set limits on parameters
EA analysis




CPU time: 30 min. for 40 processors
24 ‘genes’ to make a chromosone
Population of 250
300 generations for convergence
Cost function 40 (zero is optimal)
16
Section of the R branch
Zoom
Experiment
Simulation based
on EA results
538.30
cm-1
17
538.95
Low Ka transitions
?
18
Higher Ka transitions???
New assignments?
Experiment
Simulation based
on EA results
19
Comparison of constants
•
•
•
Parameters in blue fixed to EA value
Fit done in pGopher (pgopher.chm.bris.ac.uk)
Ground state determined separately using GSCDs
EA
/
0+/0-
1+/1-
0+
0-
1+
1-
0
0.2616215
528.9874090
529.2490305
0
0.337280202
0.337432873
0.337280202
0.337280202
0.337432873
0.337432873
0.222582091
0.222446239
0.2223509(19)
0.2225867(27)
0.22223904(6)
0.22245105(9)
0.148135953
0.147641200
0.1481570(3)
0.1481356(3)
0.14765699(3)
0.14764082(3)
0.072952
0.077707
0.07294(9)
0.07418(9)
0.077727(10)
0.076672(9)
1.526905
1.363985
1.5371(20)
1.4628(22)
1.380028(14)
1.39221(15)
-4.258586
-3.863400
-4.381(11)
-3.866(14)
-3.9923(3)
-3.7096(9)
0.017915
0.020481
0.017915
0.017915
0.020481
0.020481
0.824409
0.760675
0.824409
0.824409
0.760675
0.760675
cm-1
E
A
B
C
/
Expt (post EA analysis)
x106
528.987414(17)
0.2616215
529.282849(18)
cm-1
J
JK
K
δJ
δK
rms / cm-1
0.000138
0.000175
no.lines
971 GSCDs
2505
20
Combining the LW and EA results
Experiment
Simulation based
on EA+LW results
21
What about P branch???
Experiment
Simulation based
on EA+LW results
521.16
cm-1
22
521.42
Did the EA analysis help?
•
•
•
•
Parameters in blue fixed to EA value
Pre EA Fit done in SPFIT (spec.jpl.nasa.gov/ftp/pub/calpgm)
Post EA Fit done in pGopher (pgopher.chm.bris.ac.uk)
Ground state determined separately using GSCDs
E
/ cm-1
A
B
C
/ x106 cm-1
J
JK
K
δJ
δK
rms / cm-1
no.lines
Expt (pre EA analysis)
1+
1528.987436(15) 529.295880(20)
Expt (post EA analysis)
1+
1528.987414(17)
529.282849(18)
0.3375485(14)
0.2221886(5)
0.14765910(2)
0.337133(4)
0.2225862(14)
0.14764181(3)
0.337432873
0.22223904(6)
0.14765699(3)
0.337432873
0.22245105(9)
0.14764082(3)
0.036903(7)
0.08304(19)
0.5670(11)
0.037645(10)
0.0425(5)
0.857(4)
0.077727(10)
1.380028(14)
-3.9923(3)
0.020481
0.760675
0.076672(9)
1.39221(15)
-3.7096(9)
0.020481
0.760675
0.000117
0.000175
2358
2505
23
Acknowledgements
Dr. Brant Billinghurst (CLS Far IR beamline)
Questions???
[email protected]
[email protected]
I’m looking for a PDF in MW or IR spectroscopy.
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Contact me for info.