1. Microwave Measurements of the Tropolone-Formic Acid Doubly Hydrogen Bonded Dimer
Aaron M. Pejlovas and Dr. Stephen G. Kukolich
Agapito Serrato III and Dr. Wei Lin (University of Texas Rio Grande Valley)
ISMS June 2016

2. Earlier Work

3. Tropolone – Formic Acid
Monomer exhibits single proton tunneling
Doubly hydrogen bonded dimer with C2v(M)* sym
Concerted double proton tunneling expected
*Bunker and Jensen, Molecular Symmetry and Spectroscopy

4. PBFT MW spectrometer to measure a very congested spectrum
J′ Ka’ Kc’
J″ Ka” Kc”
obs
o-c
4 1 4
3 0 3
0.006
6 1 6
5 1 5
-0.001
6 0 6
5 0 5
-0.002
6 3 3
5 3 2
0.000
6 2 4
5 2 3
4 0 4
-0.007
7 1 7
0.004
7 0 7
7 3 5
6 3 4
0.001
7 3 4
0.002
0.003
7 2 5
-0.005
7 1 6
6 1 5
8 1 8
8 0 8
8 1 7
9 1 9
-0.003
9 0 9
10 1 9
9 1 8
0.005
PBFT MW spectrometer to measure a very congested spectrum

6. PBFT MW spectrometer to measure a very congested spectrum
J′ Ka’ Kc’
J″ Ka” Kc”
obs
o-c
4 1 4
3 0 3
0.006
6 1 6
5 1 5
-0.001
6 0 6
5 0 5
-0.002
6 3 3
5 3 2
0.000
6 2 4
5 2 3
4 0 4
-0.007
7 1 7
0.004
7 0 7
7 3 5
6 3 4
0.001
7 3 4
0.002
0.003
7 2 5
-0.005
7 1 6
6 1 5
8 1 8
8 0 8
8 1 7
9 1 9
-0.003
9 0 9
10 1 9
9 1 8
0.005
PBFT MW spectrometer to measure a very congested spectrum
Tropolone and pulsed valve kept at RT, FA at -8 °C

7. Tropolone – FA Parent(experimental) B3LYP/aug-cc-pVTZ A/MHz
Parent(experimental)
B3LYP/aug-cc-pVTZ
A/MHz
(98)
B/MHz
(25)
C/MHZ
(22)
DJ/kHz
0.0100(14)
DJK/kHz
0.102(28)
DK/kHz
13.2(81)
Δ/amu Å2
-1.46
-0.003 N 25
σ/kHz 3

8. Tropolone - FA
No tunneling observed (fit singlet a and b type transitions)
Other excited vibrational states?
Additional transitions observed may be from other weakly bound clusters with FA or H2O

9. Why was there no tunneling?
Dependent upon potential energy surface
Daly, A. M.; Bunker, P. R.; Kukolich, S. G. Communications: Evidence for Proton Tunneling from the Microwave Spectrum of the Formic Acid-Propiolic Acid Dimer. J. Chem. Phys. 132, 2010, /1.

10. cm-1
ν0-
ν0+ Å

11. Why was there no tunneling?
Dependent upon potential energy surface
Single point calculation for transition state – estimated cm-1 for barrier height (propiolic – formic only 3800 cm-1)
Separation of minima was estimated to be about the same as propiolic – formic (~ 0.8 Å)
Daly, A. M.; Bunker, P. R.; Kukolich, S. G. Communications: Evidence for Proton Tunneling from the Microwave Spectrum of the Formic Acid-Propiolic Acid Dimer. J. Chem. Phys. 132, 2010, /1.

12. Acknowledgements Dr. Stephen Kukolich
Dr. Wei Lin (University of Texas Rio Grande Valley)
Agapito Serrato III (University of Texas Rio Grande Valley)
NSF
University of Arizona