engleski

Quantum treatment of large amplitude motion in hydrogen bonded systems

The large amplitude internal motion (LAM) of the bridging hydrogen represents the key feature of H- atom transfer systems. Several methodes are employed in order to gain new insight into H-atom transfer (HAT) dynamics in acetylacetone (ACAC) and the formic acid dimer (FAD), molecules that serve as prototype systems for single and multiple HAT reactions. The infrared (IR) spectra related to the OH...O fragment of ACAC and FAD were first analyzed using a combination of a second order perturbative treatment and direct solution of the nuclear Schrodinger equation in reduced dimensionality. While capable of describing general features of IR spectra, normal mode based methods are not tailored to account for the double minimum nature of the potential surface. Further, three quantum methods capable of quantitatively describing the LAM dynamics in double well potentials are discussed. The first method is based on localized internal coordinates and in the other two methods collective LA coordinates are constructed using the minimum energy path geometries. In the two last cases, the remaining orthogonal degrees of freedom are linearized and the FAD dynamics is treated within the reaction space Hamiltonian approach. Results for the ground and excited state tunneling splittings are confronted with the results of the experimental high resolution spectrum.

acetylacetone ; formic acid dimer ; hydrogen atom transfer ; large amplitude motion ; tunneling splittings

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