Potential Energy Curves For Dissociation Research Articles

A spin-complete version of the spin-flip approach to bond breaking: What is the impact of obtaining spin eigenfunctions?

Spin-complete versions of the spin-flip configuration-interaction-singles (SF-CIS) approach have been investigated to determine the impact of making the wave function an eigenfunction of Ŝ2. The method has been implemented within an extended restricted active space configuration interaction formalism. Spin-complete results are presented for excitation energies, equilibrium geometries, and potential energy curves for dissociation of a single bond in several small molecules. The effect of different orbital choices has also been investigated. The spin-complete results are compared both to results using the original spin-flip method and to more computationally expensive benchmarks. Using spin eigenfunctions dramatically improves upon the accuracy of the SF-CIS approach.

Photoinduced dissociation of methylnitrite on Ag( [formula omitted

Electronic excitations and photoinduced electron attachment states of methylnitrite (CH 3ONO) adsorbed on Ag(1 1 1) are investigated by ab initio methods. The calculated ground state energies of the cis and trans isomers of the methylnitrite molecule are nearly degenerate, with the trans structure lower than the cis by 0.03 eV at the CI level. Experimentally, the cis isomer is estimated to be more stable by 0.03 eV. The energy of methylnitrite in its ground electronic state on the silver surface is nearly the same for both isomer configurations and changes only slightly with isomer orientation and adsorption site. In both cis and trans forms, structures in which the internal oxygen points towards the surface and the O(internal)N internuclear axis lies between 30° and 45° from the surface are favored. The calculated adsorption energy is 0.60 eV for the cis isomer. Ground and excited state potential energy curves for dissociation to CH 3O/Ag and NO (gas phase) are calculated at the CI level for both internal electronic excitations and for electron attachment excited states. The calculated ground state dissociation energy is 1.5 eV, a value 0.20 eV less than calculated for the gas phase dissociation. The metal-mediated excitation (electron attachment to the adsorbate and hole in the metal) leads to a repulsive triplet state with a vertical excitation energy of 4.7 eV and negligible singlet–triplet splitting. A second excited state produced by electron excitation within methylnitrite produces distinct singlet and triplet states. The vertical excitation occurs at 2.4 eV for the triplet state and at 3.4 eV for the singlet state. In comparing the methylnitrite/Ag(1 1 1) potential energy surface to that of gas phase methylnitrite, a shallow minimum in the first excited singlet state for the molecule appears only as a plateau in the adsorbate/metal system when the excitation is from within methylnitrite. There is a 10-fold increase in methylnitrite/silver mixing in the metal-mediated excitation as compared to the internal excitation, which may explain the surprising experimental result that dissociation does not follow metal-mediated excitation.

Electronic, Structural, and Hyperfine Interaction Investigations on Rydberg Molecules: NH4, OH3, and FH2

The geometrical structures of NH4 and OH3 were optimized at the MP2 level with the aug-cc-pvdz, aug-cc-pvtz, and aug-cc-pvqz basis set plus s-type diffuse functions. The adiabatic ionization potential, barrier height, and dissociation energy of NH4 and OH3 were calculated with the above basis set series and were extrapolated to the infinite basis set limit. The theoretical ionization potential of NH4 was in very good agreement with the experimental value. The N−H bond lengths of NH4 and NH4+ at the infinite basis set limit were obtained by parabolic interpolation around the equilibrium point. FH2 was optimized at the UHF, B3LYP, and MP2 levels. However, only a dissociated ground state was found. The potential energy curves for dissociation of the above molecules were calculated with MP2. The relative stabilities of these molecules and their isotopic counterparts are discussed. Theoretical hyperfine calculations were performed in the gas phase as well as in a neon matrix for NH4 and OH3 with a single-refer...

Isoelectronic analogs of molecular nitrogen: Tightly bound multiply charged species

The structures and stabilities of N2 and its 15 possible first-row isoelectronic analogs (CO, BF, BeNe, NO+, CF+, BNe+, O2+2, NF2+, CNe2+, OF3+, NNe3+, ONe4+, F4+2, FNe5+, and Ne6+2) have been examined using ab initio molecular orbital theory. Equilibrium structures have been obtained at a variety of levels of theory including MP3/6-311G(d) and ST4CCD/6-311+G(2df ) and dissociation energies determined at the MP4/6-311+G(3d2f ) level. Full potential energy curves for dissociation, including dissociation barriers, have been obtained at the CASSCF/6-311G(d) level. Spectroscopic constants have also been determined at this level. For the neutral and monocation analogs of N2, the calculated equilibrium geometries, dissociation energies, and spectroscopic constants are in good agreement with the experimental values. The dication analogs of N2, namely O2+2, NF2+, and CNe2+, are all found to be kinetically stable species lying in deep potential wells. In particular, the hitherto unobserved NF2+ dication is predicted to have a short equilibrium bond length (1.102 Å) and a large barrier (445 kJ mol−1) to dissociation to N++F+. Thus NF2+ should be experimentally accessible in the gas phase. The (experimentally known) O2+2 dication is predicted to contain the shortest bond between any two heavy atoms, our best estimate of the bond length being 1.052 Å. The first excited state (A 3Σ+u) of O2+2 is predicted to be unbound, and observed metastable decomposition processes are reinterpreted in terms of the ground-state (X 1Σ+g) potential surface. In agreement with previous theoretical studies, we find that CNe2+ is a kinetically stable species, albeit with a relatively long C–Ne bond length. The OF3+ trication is calculated to have a relatively short bond but lies in a well of depth only 23 kJ mol−1. The potential energy curves of the other highly charged species are found to be purely repulsive.