Quantum Effects for a Proton in a Low-Barrier, Double-Well Potential: Core Level Photoemission Spectroscopy of Acetylacetone

Abstract

We have performed core level photoemission spectroscopy of gaseous acetylacetone, its fully deuterated form, and two derivatives, benzoylacetone and dibenzoylmethane. These molecules show intramolecular hydrogen bonds, with a proton located in a double-well potential, whose barrier height is different for the three compounds. This has allowed us to examine the effect of the double-well potential on photoemission spectra. Two distinct O 1s core hole peaks are observed, previously assigned to two chemical states of oxygen. We provide an alternative assignment of the double-peak structure of O 1s spectra by taking full account of the extended nature of the wave function associated with the nuclear motion of the proton, the shape of the ground and final state potentials in which the proton is located, and the nonzero temperature of the samples. The peaks are explained in terms of an unusual Franck-Condon factor distribution.

TIMPZ: An Exquisite Building Block for Metal/Hydrogen Coordination Polymers

“…Experimentally, the δ > 10 downfield shift and sharp N–H peak for weak acidic hydrogen supports the intramolecular H‐bond formation . Therefore, in the case of the neutral TIMPZ, the N(2)–H ··· N(1) TIMPZ H‐NMR signals in [D 8 ]THF located at δ = 18.10 ppm suggests a low barrier N–H ··· N hydrogen bond . This can also be evidenced by the infrared frequencies of the N–H stretching observed at ≈ 1000–600 cm –1 …”

Elucidating Solvent Effects on Strong Intramolecular Hydrogen Bond: DFT‐MD Study of Dibenzoylmethane in Methanol Solution

“…[10,[15][16][17][18][19][20][21][22][23][24][25][26][27][28] The perplexity caused by the relative stability of the asymmetric and symmetric DBM's protic tautomers is due to the inability of experimental scattering and spectroscopic techniques to resolve ultrafast proton motion in the hydrogen bond, but also possibly due to various experimental conditions and aggregate states in which DBM was studied. [10,[15][16][17][18][19][20][21][22][23][24][25][26][27][28] The perplexity caused by the relative stability of the asymmetric and symmetric DBM's protic tautomers is due to the inability of experimental scattering and spectroscopic techniques to resolve ultrafast proton motion in the hydrogen bond, but also possibly due to various experimental conditions and aggregate states in which DBM was studied.…”

“…Enolic DBM attracted a lot of experimental and theoretical attention due to a conflicting assignment of its intramolecular hydrogen bond structure. [10,[15][16][17][18][19][20][21][22][23][24][25][26][27][28] The perplexity caused by the relative stability of the asymmetric and symmetric DBM's protic tautomers is due to the inability of experimental scattering and spectroscopic techniques to resolve ultrafast proton motion in the hydrogen bond, but also possibly due to various experimental conditions and aggregate states in which DBM was studied. [23,26] The potential energy barrier for the proton transfer in the gas phase was estimated to be approximately between 1 and 2 kcal/mol [22] and free energy calculations [22,26] favored the asymmetric over the symmetric tautomer.…”

Unusual Spectroscopic and Electric Field Sensitivity of Chromophores with Short Hydrogen Bonds: GFP and PYP as Model Systems

“…The search for functionally important LBHBs in proteins has been rather difficult however [26] [27] [28], since no single approach can provide unambiguous evidence for the degree of delocalization [19]. X-ray and neutron diffraction are utilized to characterize the nuclear coordinates, while energetic information is mostly extracted from spectroscopic studies frequently combined with isotope substitution [2] [10] [29] [30] [31] [32] [33].…”