Adam J. Fleisher Philip J. Morgan David W. Pratt Department of Chemistry University of Pittsburgh Non-symmetric push-pull molecules in the gas phase: High resolution Stark spectroscopy of m-aminobenzoic acid. WF-08

GOAL: Use the permanent electric dipole moments of the two conformers to aid in assignment b and explain their solvation properties. Evidence for Two Rotamers a Fig. 2 in He, Y., Wu, C., Kong, W. J. Chem. Phys. 121, 8321, (2004). b Reese, J., Nguyen, T.V., Korter, T.M., Pratt, D.W. J. Am. Chem. Soc. 126, 11387, (2004).

Wavenumber (cm -1 ) I II He, Y., Wu, C., Kong, W. J. Chem. Phys. 121, 8321, (2004). Fluorescence Excitation Spectrum

High Resolution Spectrum 2.88 cm -1 MABA I – cm -1

High Resolution Experiment W. A. Majewski, J. F. Pfanstiel, D. F. Plusquellic, and D. W. Pratt, in Laser Techniques in Chemistry, edited by A. B. Myers and T. Rizzo (Wiley, New York, 1995), 101.

Hamiltonian and Optics

Inertial Parameters Band IBand II S0S0 S1S1 S0S0 S1S1 A (MHz) B (MHz) C (MHz) ΔI (amu Å 2 )-0.750(6)-0.377(7)-0.76(2)-0.39(2) L/G LW (MHz)60 / 3644 / 36

Stark Shifts in MABA I 650 MHz 211 V/cm 423 V/cm 0 V/cm 650 MHz

Stark Parameters MABA IMABA II ExperimentTheory a ExperimentTheory a S0S0 III μaμa 2.1(1) (1)2.62 μbμb 0.7(2) (1)1.73 μcμc 0.0(1) (1)0.94 μ S1S1 μaμa 5.7(1) (1)5.77 μbμb 0.0(2) (1)3.04 μcμc 0.0(1) (1)0.00 μ a M.J. Frisch et. al. Gaussian 03 (Gaussian, Inc., Wallingford, CT, 2004). Dipole moments determined using the aug-cc-pvdz basis set (mp2 and CIS theories) on previously optimized geometries (M05-2X/6-31+G* for S 0, and CIS/6-31+G* for S 1 ).

Fluorescence Excitation Spectrum Wavenumber (cm -1 ) He, Y., Wu, C., Kong, W. J. Chem. Phys. 121, 8321, (2004). I II

Dipole Projections S0S0 S1S1 II (red) I (blue)

II (red)I (blue) Push-Pull Excitation M.J. Frisch et. al. Gaussian 03 (Gaussian, Inc., Wallingford, CT, 2004). Density difference maps of S 1  S 0 calculated at CIS / 6-31+G* PABA from Figs. 7 and 8 in Mitchell, D.M., Morgan, P.J., Pratt, D.W. J Phys Chem. A. 112, 12597, (2008). PABA Δμ = 3.5 DΔμ = 3.6 DΔμ = 1.1 D S1S1

Solvent Stabilization Fig. 5 in He, Y., Wu, C., Kong, W. J. Phys. Chem. A. 109, 748, (2005). II (cm -1 )I (cm -1 ) E μμ in S E μμ in S ΔE μμ (Shift)

MABA vs. PABA He, Y., Wu, C., Kong, W. J. Phys. Chem. A. 109, 748, (2005). He, Y., Wu, C., Kong, W. J. Phys. Chem. A. 109, 2809, (2005). Mitchell, D.M., Morgan, P.J., Pratt, D.W. J Phys Chem. A. 112, 12597, (2008). A (cm -1 ) B (cm -1 ) PABA (cm -1 ) E μμ in S E μμ in S ΔE μμ (Shift) Exp. Shift-100? +17 θ1θ1 θ2θ2 ϕ r II I PABA

Summary The permanent dipole moments of m-aminobenzoic acid were determined in the gas phase. The existence of two rotamers in the supersonic expansion was confirmed, and their electronic origins were assigned. The experimental dipole moment results were used to postulate cluster structures. The curious solvatochromic trends previously observed for MABA and PABA can now be explained.

Justin Young Patrick Walsh Diane Miller Marquette University Jessica Thomas Ryan Bird Casey Clements Dr. David W. Pratt University of Pittsburgh Dr. David Plusquellic NIST, jb95 development Dr. David Borst Intel, Stark development Acknowledgments

Occupied Unoccupied MABABenzoic Acid Aniline Frontier Orbitals M.J. Frisch et. al. Gaussian 03 (Gaussian, Inc., Wallingford, CT, 2004).

CW Tunable UV Laser Argon Ion Laser (7 W) Ring Dye Laser (85 mW) Frequency Doubler Reference Station I 2 tube Tunable UV laser beam (300 µW) Monochromator Interferometer

Inertial Parameters Band IBand II S0S0 S1S1 S0S0 S1S1 A (MHz) B (MHz) C (MHz) ΔI (amu Å 2 )-0.750(6)-0.377(7)-0.76(2)-0.39(2) Κ TM a/b/c (%)16 / 84 / 022 / 78 / 0 Origin (30) (30) # lines / OMC (MHz)380 / / 3.1 L/G LW (MHz)60 / 3644 / 36

PMT Boxcar Integrator Computer Nd 3+ :YAG Laser Dye Laser Mirror Filter Iris KDP Crystal He Vacuum Chamber hh Pulsed UV Laser

Stark Shifts in MABA I 0.05 cm V/cm 423 V/cm 846 V/cm 1269 V/cm 0 V/cm

Stark Shifts in MABA II 650 MHz 211 V/cm 0 V/cm

Stark Shifts in MABA I 0.05 cm -1 0 V/cm 211 V/cm 423 V/cm 846 V/cm 1269 V/cm

A

A 3545

BA

AN C=0.62