1. Chirped Pulse Microwave Spectroscopy on Methyl Butanoate
11/12/2018
Chirped Pulse Microwave Spectroscopy on Methyl Butanoate
Alicia Hernandez-Castillo, Brian Hays, Chamara Abeysekara, and Timothy Zwier 1

2. 11/12/2018
Motivation
Methyl Butanoate has the major groups to compare to biofuels
The decomposition products can proceed through several channels
The oxidative chemistry has been modelled before 2

3. 11/12/2018
Theory
Conformational search performed with the MM2* force field using MacroModel
Optimized structures at the MP2/aug-cc-pVTZ level of theory using Guassian 09 with ZPVE pt gg tt tg 3

4. Experimental
Guzik 40 GS/s digitizer
13 GHz bandwidth

5. Experimental

6. Spectrum 1.5 million averages 25 averages/gas pulse 10% TWTA Gain
15 PSI He

7. Conformation-Specific Spectroscopy
11/12/2018
Conformation-Specific Spectroscopy
The initial analysis was done using Strong Field Coherence Breaking technique to find which transitions belonged to which conformer
Will be discussed in full detail in tomorrow’s talks 7

8. Conformation-Specific Spectroscopy
11/12/2018
Conformation-Specific Spectroscopy
The initial analysis was done using Strong Field Coherence Breaking technique to find which transitions belonged to which conformer
Will be discussed in full detail in tomorrow’s talks
TG03 and TG04 in the Spectroscopy in Atmospheric Chemistry Mini-Symposium
Tuesday afternoon 8

9. Spectrum

10. Tunneling Splitting Fit using the XIAM program
C. C. Lin and J. D. Swalen, Rev. Mod. Phys. 31, (1959)
H.Hartwig and H.Dreizler, Z. Naturforsch 51a, (1996)

11. Methyl rotor Tunneling SplittingA E A
Conformer tt
E A
Conformer tg A *

12. Methyl rotor Tunneling SplittingA E A
Conformer tt
E A
Conformer tg A *

13. Methyl rotor Tunneling SplittingA E E A
E&A
E A E A E A E
Conformer tt
E A
E A
Conformer 2 A *

14. Internal Rotor Fit tt conformer Experimental Theoretical A (MHz)
11/12/2018
Internal Rotor Fit
Experimental
Theoretical
A (MHz)
(25)
B (MHz)
(13)
C (MHz)
(91)
DJ (kHz)
0.052(20)
DJK (kHz)
dJ (kHz)
0.0117(24)
V3 (cm-1)
395(24)
F0 (GHz)
150.3(8.0)
epsilon (rad)
-2.67 (20)
delta (rad)
0.468(85) N 32
rms (MHz)
Jmax 12
tt conformer 14

15. Internal Rotor Fit tg conformer Experimental Theoretical A (MHz)
(17)
B (MHz)
(24)
C (MHz)
(28)
DJ (kHz)
0.477(38)
DJK (kHz)
-6.03(26)
DK (kHz)
51.5(2.3)
dJ (kHz)
-0.083(29)
V3 (cm-1)
426(16)
F0 (GHz)
160.8(5.3)
epsilon (rad)
-6.02(32)
delta (rad)
0.5404(49) N 47
rms (MHz)
Jmax 7
tg conformer

16. Conformers Found No Conformer gg or pt found
No evidence for more conformers pt gg tt tg

17. Conformers Found No Conformer gg or pt found
No evidence for more conformers
Conformational Cooling pt gg tt tg

18. Relative Populations Using rotation diagram method with the form:
J. M. Oldham, C. Abeysekara, et al. J. Chem. Phys. 141, (2014)

19. Relative Populations
tt tg 40% 60%

20. Future Work Are more conformers available in the jet cooled spectrum
Look for more conformers and excited vibrational states in room temperature cell
Pyrolysis on methyl butanoate to look for radicals such as:

21. Acknowledgements
The Zwier Group
#55152-ND6