Potential energy surface

About: Potential energy surface is a research topic. Over the lifetime, 11674 publications have been published within this topic receiving 307691 citations.

Dynamical resonances accessible only by reagent vibrational excitation in the F + HD->HF + D reaction.

Abstract: Experimental limitations in vibrational excitation efficiency have previously hindered investigation of how vibrational energy might mediate the role of dynamical resonances in bimolecular reactions. Here, we report on a high-resolution crossed-molecular-beam experiment on the vibrationally excited HD( v = 1) + F → HF + D reaction, in which two broad peaks for backward-scattered HF( v ′ = 2 and 3) products clearly emerge at collision energies of 0.21 kilocalories per mole (kcal/mol) and 0.62 kcal/mol from differential cross sections measured over a range of energies. We attribute these features to excited Feshbach resonances trapped in the peculiar HF( v ′ = 4)–D vibrationally adiabatic potential in the postbarrier region. Quantum dynamics calculations on a highly accurate potential energy surface show that these resonance states correlate to the HD( v ′ = 1) state in the entrance channel and therefore can only be accessed by the vibrationally excited HD reagent.

Solvation ultrafast dynamics of reactions. 8. Acid-base reactions in finite-sized clusters of naphthol in ammonia, water, and piperidine

Abstract: In this contribution, studies of the dynamics of proton-transfer reactions in solvent cages are presented, building on earlier work [Breen, J. J.; et al. J. Chem. Phys. 1990, 92, 805. Kim, S. K.; et al. Chem. Phys. Lett. 1994, 228, 369]. The acid-base system studied in a molecular beam is 1-naphthol as a solute and ammonia, piperidine, or water as the solvent, with the number of solvent molecules (n) varying. The rates and threshold for proton transfer have been found to be critically dependent on the number and type of solvent molecules: n = 2 for piperidine and n = 3 for ammonia; no proton transfer was observed for water up ton = 21. With subpicosecond time resolution, we observe a biexponential transient for the n = 3 cluster with ammonia. From these observations and the high accuracy of the fits, we provide the rate of the proton transfer at short times and the solvent reorganization at longer times. From studies of the effect of the total energy, the isotope substitution, and the number and type of solvent molecules, we discuss the nature of the transfer and the interplay between the local structure of the base solvent and the dynamics. The effective shape of the potential energy surface is discussed by considering the anharmonicity of the reactant states and the Coulombic interaction of ion-pair product states. Tunneling is related to the nature of the potential and to measurements specific to the isotope effect and energy dependence. Finally, we discuss a simple model for the reaction in finite-sized clusters, which takes into account the proton affinity and the dielectric shielding of the solvent introduced by the local structure.

Photodissociation dynamics of pyrrole: evidence for mode specific dynamics from conical intersections.

Abstract: The H and D atom elimination mechanisms in the photodissociation of jet cooled pyrrole and pyrrole-d1 have been studied by photofragment velocity map imaging. The molecules were excited to the 1 1A2 (πσ*) state at λ = 243 nm and to the 1 1B2 (ππ*) state at λ = 217 nm. H/D atoms were detected by (2 + 1) resonance enhanced multiphoton ionization (REMPI) at λ = 243 nm. The analysis of the images and the resulting translational energy distributions from the 1 1A2 state demonstrates the existence of two decay pathways, fast mode-specific cleavage of the NH bond in the excited state (channel A) and internal conversion (IC) to the electronic ground state (S0) followed by unimolecular decomposition of the vibrationally hot S0 molecules (channel B). The angular distributions of the H/D atoms from the direct dissociation in the excited state are strongly anisotropic, whereas the decay of the S0 molecules leads to spatially isotropic distributions. The results at λ = 217 nm indicate that the 1 1B2 state undergoes an ultrafast radiationless transition to 1 1A2 followed by the abovementioned direct mode-specific NH bond fission on the 1 1A2 potential energy surface (channel A′) or conversion to S0 and subsequent unimolecular decomposition (channel B′). The latter pathway may also be initiated by a direct relaxation from 1 1B2 to S0. The anisotropy parameter of β ≈ −1 for the direct NH bond fission at λ = 217 nm is in accordance with the expectations for a perpendicular electronic excitation and a dissociation lifetime that is short compared to the rotational period of the molecules. The fast decay dynamics of both excited electronic states can be rationalized with reference to the theoretically predicted conical intersections between the ππ*, πσ*, and S0 potential energy surfaces and the antibonding nature of the πσ* potential energy surface with respect to the NH bond [A. L. Sobolewski, W. Domcke, C. Dedonder-Lardeux and C. Jouvet, Phys. Chem. Chem. Phys. 2002, 4, 1093].

Ab initio global potential-energy surface for H5(+) --> H3(+) + H2.

Abstract: An accurate global potential-energy surface (PES) is reported for H5(+) based on more than 100,000 CCSD(T)/aug-cc-pVTZ ab initio energies. This PES has full permutational symmetry with respect to interchange of H atoms and dissociates to H3(+) and H2. Ten known stationary points of H5(+) are characterized and compared to previous ab initio calculations. Quantum diffusion Monte Carlo calculations are performed on the PES to obtain the zero-point energy of H5(+) and the anharmonic dissociation energy (D0) of H5(+) --> H3(+) + H2. The rigorous zero-point state of H4D+ is also calculated and discussed within the context of a strictly classical approach to obtain the branching ratio of the reaction H4D+ --> H3(+) + HD and H2D+ + H2. Such an approach is taken using the PES and critiqued based on the properties of the quantum zero-point state. Finally, a simple procedure for adding the long range-interaction energy is described.