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.

A theoretical study of vibrational mode coupling in H5O2

Abstract: The vibrational mode coupling in the protonated water dimer is investigated by performing two types of quantum calculations of the vibrational levels of H5O2+ and D5O2+, utilizing the OSS3(p) potential energy surface by Ojamae et al. [L. Ojamae, I. Shavitt, and S. J. Singer, J. Chem. Phys. 109, 5547 (1998)]. One is four-dimensional (4D), treating only the central O⋯H(D)+⋯O moiety. Three of the four modes considered, the asymmetric stretch and the two bends, are largely the vibrations of the central proton, while the fourth mode is essentially the O⋯O stretching vibration. The vibrational levels of O⋯H(D)+⋯O are calculated rigorously, as fully coupled (FC), and also in an adiabatic (3+1)D approximation, where the proton asymmetric stretch is treated as adiabatically separated from the other three degrees of freedom. The second set of calculations, designated VCI, is full-dimensional, 15D; it is performed by the code MULTIMODE, which does configuration interaction (CI) calculations using a basis determined ...

Hydrogen Bonding and Proton Transfer in the Ground and Lowest Excited Singlet States of o-Hydroxyacetophenone

Abstract: The potential energy surface of the ground state and lowest lying singlet of o-hydroxyacetophenone was calculated at the ab initio SCF and CIS levels, respectively, using a split-valence basis set to which was added polarization functions on atoms involved in the intramolecular H-bond. Whereas these potentials each contain one minimum corresponding to the normal form and a second well for the proton-transferred tautomer, only one minimum appears in these potentials after correlation is added. SO S1 excitation hence induces the tautomerization associated with intramolecular proton transfer from the hydroxyl to the carbonyl oxygen. The excited state proton transfer may involve a nonradiative transition from the Sl(nn*) state to Sl(nn*). The vibrational spectra of the two tautomers have certain strong differences. Anharmonic adiabatic treatment of the OH* 9 segment of the molecule leads to improved reproduction of experimentally observed v ( 0 9) and v(0H) frequencies.

A new form of kinetic isotope effect. Dynamic effects on isotopic selectivity and regioselectivity.

Abstract: The intramolecular H/D kinetic isotope effect in the ene reaction of singlet oxygen with tetramethylethylene is studied using quasiclassical direct dynamics calculations on a B3LYP/6-31G* potential energy surface. Starting from the area of the energy surface around a valley-ridge inflection point, random trajectories lead to predominantly H abstraction over D abstraction, despite the symmetry of the surface and the absence of a barrier to either reaction. This demonstrates a new form of kinetic isotope effect, unrelated to the usual effect of zero-point energies on barriers. Dynamics calculations on the reaction of cis-2-pentene predict the experimentally observed mixture of regioisomeric products, while the minimum-energy path leads to only one product. For energy surfaces containing two adjacent saddle points, dynamics effects are important for understanding both product and isotopic selectivity, and this should be considered in the interpretation of experimental results.

Quantum study of vibrational excitation in the three‐dimensional collisions of CO2 with rare gas atoms

Abstract: A combined vibrational close‐coupling and rotational infinite order sudden technique is described for calculating vibrational excitation cross sections σvv′ for the three‐dimensional collisions of atoms with linear triatomic molecules. The method treats anharmonic, Coriolis, and vibrational angular momentum terms in the molecular Hamiltonian accurately, and is applicable to any realistic potential energy surface expressed in numerical or functional form. Application of the method to X–CO2(v1v2λv3) collisions, where X = He, Ne, or Ar, is described. An accurate anharmonic CO2 potential, expressed in terms of bond and angle displacements, is employed. The X–CO2 interaction potentials are more approximate and are expanded in terms of atom–atom pair potentials. Calculations of σvv′, over a grid of energies sufficient to give rate coefficients kvv′ for transitions between the low‐lying states of CO2 for temperatures up to 300 K, have been performed. Propensities for particular collisional excitations involving ...

Communication: Ro-vibrational control of chemical reactivity in H+CH₄→ H₂+CH₃: full-dimensional quantum dynamics calculations and a sudden model.

Abstract: The mode-selective chemistry of the title reaction is studied by full-dimensional quantum dynamics simulation on an accurate ab initio potential energy surface for vanishing total angular momentum. Using a rigorous transition state based approach and multi-configurational time-dependent Hartree wave packet propagation, initial state-selected reaction probabilities for many ro-vibrational states of methane are calculated. The theoretical results are compared with experimental trends seen in reactions of methane. An intuitive interpretation of the ro-vibrational control of the chemical reactivity provided by a sudden model based on the quantum transition state concept is discussed.