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

Earlier Work

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

PBFT MW spectrometer to measure a very congested spectrum J′ Ka’ Kc’ J″ Ka” Kc” obs o-c 4 1 4 3 0 3 4776.994 0.006 6 1 6 5 1 5 4879.911 -0.001 6 0 6 5 0 5 5051.614 -0.002 6 3 3 5 3 2 5169.534 0.000 6 2 4 5 2 3 5237.764 4 0 4 5444.692 -0.007 7 1 7 5683.893 0.004 7 0 7 5855.119 7 3 5 6 3 4 6030.552 0.001 7 3 4 6038.775 0.002 6089.936 0.003 7 2 5 6141.604 -0.005 7 1 6 6 1 5 6257.955 8 1 8 6484.354 8 0 8 6646.059 6722.206 8 1 7 7133.512 9 1 9 7281.295 -0.003 7351.443 9 0 9 7426.650 7986.682 10 0 10 8199.868 10 1 9 9 1 8 8856.853 11 1 11 10 1 10 8865.250 0.005 11 0 11 8968.743 PBFT MW spectrometer to measure a very congested spectrum

PBFT MW spectrometer to measure a very congested spectrum J′ Ka’ Kc’ J″ Ka” Kc” obs o-c 4 1 4 3 0 3 4776.994 0.006 6 1 6 5 1 5 4879.911 -0.001 6 0 6 5 0 5 5051.614 -0.002 6 3 3 5 3 2 5169.534 0.000 6 2 4 5 2 3 5237.764 4 0 4 5444.692 -0.007 7 1 7 5683.893 0.004 7 0 7 5855.119 7 3 5 6 3 4 6030.552 0.001 7 3 4 6038.775 0.002 6089.936 0.003 7 2 5 6141.604 -0.005 7 1 6 6 1 5 6257.955 8 1 8 6484.354 8 0 8 6646.059 6722.206 8 1 7 7133.512 9 1 9 7281.295 -0.003 7351.443 9 0 9 7426.650 7986.682 10 0 10 8199.868 10 1 9 9 1 8 8856.853 11 1 11 10 1 10 8865.250 0.005 11 0 11 8968.743 PBFT MW spectrometer to measure a very congested spectrum Tropolone and pulsed valve kept at RT, FA at -8 °C

Tropolone – FA Parent(experimental) B3LYP/aug-cc-pVTZ A/MHz   Parent(experimental) B3LYP/aug-cc-pVTZ A/MHz 2180.7186(98) 2191.3931 B/MHz 470.87390(25) 474.39567 C/MHZ 387.68984(22) 389.97457 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

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

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, 201101/1.

cm-1 ν0- ν0+ Å

Why was there no tunneling? Dependent upon potential energy surface Single point calculation for transition state – estimated 15000 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, 201101/1.

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