Vibrational specificity of proton-transfer dynamics in ground-state tropolone

Abstract

The vibrational dependence of large-amplitude proton transfer taking place in the ground electronic state (¹A₁) of tropolone has been explored by implementing a coherent variant of the stimulated emission pumping (SEP) technique within the framework of two-color resonant four-wave mixing (TC-RFWM) spectroscopy. The lowest 1700 cm⁻¹ portion of this potential surface has been interrogated under ambient bulk-gas conditions, enabling rotationless term energies (T_v+) and tunneling-induced bifurcations to be extracted for 43 assigned vibrational features of a₁ and b₂ symmetry. The resulting values of reflect the state-specificity long attributed to the hydron-migration pathways of tropolone and range in magnitude from 0.0 cm⁻¹ to 17.8 cm⁻¹, where the former implies essentially complete quenching of unimolecular dynamics whilst the latter represents nearly a twenty-fold increase in reaction rate over that of the zero-point level. This vibrational mediation of tunneling behavior is discussed in terms of attendant atomic displacements and permutation-inversion symmetries, with choreographed motion of the five-member reaction site () found to exert the most significant influence on the efficacy of proton transfer.