1. ASSIGNMENT OF THE PERFLUOROPROPIONIC ACID-FORMIC ACID COMPLEX AND THE DIFFICULTIES OF INCLUDING HIGH Ka TRANSITIONS
Daniel A. Obenchain, Eric A. Arsenault, Wei Lin, Stewart E. Novick, & S. A. Cooke

2. Perfluoropropionic Acid
J. Mol. Spectrosc. 275 (2012) 1-4

3. Perfluoropropionic Acid Hydrates
J. Chem. Phys A. 119 (2015)

4. Perfluoropropionic Acid Hydrates
H2O-PFPA
(H2O)2-PFPA

5. Spectra Collection
10k averages on a chirped broadband microwave spectrometer
7-13 GHz
Additional measurements made on a cavity spectrometer
GHz
Argon bubbled through the a mixture of perfluoropropionic acid and formic acid in a 1:1 volume ratio at 1.2 atm

6. Observed Spectra B+C is  800 MHz
Observed well resolved a-type R-branch transitions from J=8 to J=14 in the broadband spectrum

7. Ka>2 Ka=0 Ka=2 Ka=2 Ka=1 J= 13-12 region 10,000 averages broadband
Rough prediction based on initial fits
Ka>2
Ka=0
Ka=2
Ka=2
Ka=1

8. Fit from only Ka=0,1 transitions
Fits of the spectra
Fit from only Ka=0,1 transitions A0
1524.1(27) MHz A1
1483.3(24) MHz B0
(19) MHz B1
(18) MHz C0
(14) MHz C1
(13) MHz
DJ,0
0.0813(65) kHz
DJ,1
0.0475(62) kHz N 20
rms
3.9 kHz
No combination of transitions appears to produce quality fits that accurately predict new transitions
Best fits so far include only Ka=0 and a few Ka=1 a-type transitions

9. Cavity Spectra
250 Averages
150 Averages
Ka=3
MHz
MHz

10. Cavity Spectra No additional splitting observed
Now able to access J=5 to J=23
Only fits with Ka=0 are decent, loses predictability with higher Ka

11. Trifluoroacetic acid-formic acid

12. Perfluoroacetic acid-formic acid

13. Formic Acid-Acetic Acid complex
Prof. Brian Howard’s group at Oxford tackled a double proton transfer problem
Observed both double proton transfer, and methyl internal rotation
Tayler, M. C. D., Ouyang, B., Howard, B. J., J. Chem. Phys. 134 (2011)

14. Formic Acid-Acetic Acid complex
Howard states that the fits were heavily dependent on 2nd order corrections to the Coriolis terms.
So far, our attempts at including these terms have not produced quality fits.
Tayler, M. C. D., Ouyang, B., Howard, B. J., J. Chem. Phys. 134 (2011)

15. Ground State Dipole moment predictions a = 2.7 D b = 0.3 D
c = 0.3 D
Gaussian 09, using APF-D density function, with a G(2d,2p) basis set

16. Ground State
Gaussian 09, using APF-D density function, with a G(2d,2p) basis set

17. Possible transition states
Double proton transfer TS
1500 cm-1 above minimum

18. Possible transition states
Acid rotation TS
400 cm-1 above minimum
Same Structure, different views

19. Cause of the doubled spectrum
No inversion of a, we are likely not observing cross-state a-type transitions We have made attempts at assignment of the enriched deuterium spectra, but no results have come of it as of yet

20. Internal Rotation of -CF3 group
Splitting observed?
Internal Rotation
Proton Transfer
Perfluoropropionic Acid No -
Perfluoropropionic Acid-H2O
Perfluoropropionic Acid-(H20)2
Perfluoropropionic Acid- Cyclopropanecarboxylic Acid
Trifluoroacetic Acid
Yes
Yes (3rd excited state)
Trifluoroacetic Acid-Formic Acid
Trifluoroacetic Acid-H2O
Yes (water inversion)
Acetic Acid-Formic Acid
Perfluoropropionic Acid-Formic Acid ?

21. Internal Rotation of -CF3 group

22. Suggestions?
We welcome anyone with suggestions or comments with this problem to contact us “We hope the present method’s simplicity renews the inspiration to study, at high resolution, similarly large and ‘loose’ molecules where there is more than one large amplitude internal motion present” Tayler, M. C. D., Ouyang, B., Howard, B. J., J. Chem. Phys. 134 (2011)

23. Acknowledgements
Cluster at Wesleyan University funded NSF Grant # CNS
Prof. Wei Lin at University of Texas Rio Grande Valley
Novick/Pringle/Cooke Groups

24. Internal Rotation of -CF3 group
Splitting observed?
Internal Rotation
Proton Transfer
Perfluoropropionic Acid
J. Mol. Spectrosc. 275 (2012) 1-4
Perfluoropropionic Acid-H2O
J. Chem. Phys A. 119 (2015)
Perfluoropropionic Acid-(H20)2
Perfluoropropionic Acid- Cyclopropanecarboxylic Acid
S. Antolinex, H. Driezler, V. Storm, D. H. Sutter, J. L. Alonso. Z. Naturforsch. 52a, (1997)
Trifluoroacetic Acid
J. Mol. Spectrosc. 113, ( 1985)
Trifluoroacetic Acid-Formic Acid
Chem. Phys. 148 ( 1990)
Trifluoroacetic Acid-H2O
J. Phys. Chem. A 2007, 111,
Acetic Acid-Formic Acid
Tayler, M. C. D., Ouyang, B., Howard, B. J., J. Chem. Phys. 134 (2011)
Perfluoropropionic Acid-Formic Acid
This work