Friedrich Grein

Potential energy surfaces of ozone in its ground state and in the lowest-lying eight excited states

Potential energy surfaces of the ground state and the lowest eight excited states of ozone which correlate with the three fragmentation limits O(‘P,) +Or(X “Z;), O(‘P,) +Or(a ‘4) and O(‘D,) +Oz(a ‘4) are calculated employing multireference contiguration interaction (MRD-CI) treatments in a Gaussian A0 basis. Vertical and adiabatic transition energies as well as dissociation energies based on the optimized energy surface are presented. The transition moments between the ground state and the excited singlet states are also computed as a function of geometry and are employed to simulate Wulf, Chappuis and Huggins absorption bands. Some aspects about ozone predissociation and photodissociation and its formation are discussed.

Rotationally inelastic scattering and potential calculations for He + CH4

In a crossed molecular beam experiment total differential cross sections and differential energy loss spectra have been measured for Ne + CH4 at 88·8 meV. The energy loss spectra taken at centre-of-mass deflection angles from 45° to 145° show appreciable energy transfer in the backward direction with a maximal energy transfer corresponding to final rotational states of j′ = 4. The total differential cross sections exhibit diffraction oscillations in the forward direction. These two data sets are compared with calculations performed in the accurate centrifugal sudden approximation both for the A- and T-symmetry of the CH4 molecule. The non-spherical potential surface, which includes the anisotropic T 3 and T 4 is determined from accurate SCF-calculations and a damped dispersion contribution using the HFD-model. The general features of the experimental data are reproduced using a simple universal damping function. However, discrepancies concerning the isotropic potential well depth and the repulsive anisotr...

Density functional theory and multireference configuration interaction studies on low-lying excited states of TiO2

Using density functional theory at the BPW916-311+G(3df) level, optimized geometries and energies of the lowest singlet, triplet, and quintet A(1), A(2), B(1), B(2)(C(2v)) states of the TiO(2) molecule were obtained. TiO(2) has a (1)A(1) ground state in C(2v) symmetry. Adiabatic excitation energies of the low-lying singlet and triplet states range from 2.1 to 3.0 eV. The (1,3)A(2) states optimize at bond angles of about 140 degrees , lying only 0.06 eV below linear (1,3)Delta(u), whereas (1,3)B(1) and (1,3)B(2), with bond angles of 120 degrees and 96 degrees , respectively, lie 0.3-0.4 eV below the respective (1,3)Pi(u) or (1,3)Delta(u) states. Minima with short O-O distances of approximately 1.46 A, at energies of 4.2 and 4.7 eV, were found for (1)A(1) and (3)A(1). The C(2v) minima of the lowest (1)B(1) and (3)B(1) states are saddle points, suggesting lower-energy structures in C(s) symmetry. The C(2v) quintet states start at energies of 5.7 eV. Multireference configuration interaction (MRCI) methods, employing a polarized valence triple-zeta basis set, lead to similar geometries and energies. MRCI vertical excitation energies up to 4.6 eV and oscillator strengths are given. The calculated excitation energy of 2.2 eV for (1)B(2) agrees well with 2.3 eV from a fluorescence spectrum. The vertical electron detachment energy of TiO(2) (-) is 1.5 eV, in good agreement with 1.6 eV from anion photoelectron spectroscopy. An observed second photoelectron band corresponds to (1)B(2) and/or (3)B(2), but the assignment of a third band could not be verified. Vibrational frequencies, ionization energies, electron affinities, and dissociation energies are given.

Dipole and quadrupole moments of small molecules. An ab initio study using perturbatively corrected, multi-reference, configuration interaction wave functions

Abstract An ab initio study of the dipole and quadrupole moments of 17 small molecules, O2, NO, N2, CO, HF, HCl, N2O, CO2, OCS, CS2, NH3, C2H2, O3, SO2, H2O, H2CO and C2H2, is reported. The moments are obtained as expectation values from multi-reference, configuration interaction wave functions corrected perturbatively by the so-called Bk procedure. All the wave functions employ the one-particle Gaussian basis sets of Sadlej that were specifically designed for the calculation of electric properties. The results are in generally good agreement with previous high-quality computations and experiment where available.

Efficient calculation of electron paramagnetic resonance g-tensors by multireference configuration interaction sum-over-state expansions, using the atomic mean-field spin–orbit method

Using the multireference configuration interaction method due to Grimme and Waletzke, combined with the atomic mean-field approximations for the efficient calculation of spin–orbit matrix elements, the g-tensors in second-order perturbation theory have been calculated for the main group radicals CO+, CN, BO, BS, MgF, AlO, O2, HCO, H2O+, NO2, CO2−, NF2, NO22−, O3−, ClO2, and H2CO+, and for the transition metal compounds ZnH, ZnF, and TiF3, using explicit sum-over-state expansions for up to 20 excited states. In most cases, a valence triple-zeta basis set with polarization functions has been employed. It is shown that the addition of diffuse functions to this basis set does not improve the g-tensor results, and in several instances leads to slower convergence of the sum-over-state expansion. The calculated g-tensors are in good agreement with experimental values, and with our previous multireference configuration interaction results available for 9 of the 19 radicals. Our results are shown to be equivalent ...

Benchmark ab initio calculations of formaldehyde, H2CO

Abstract A review of ab initio calculations on the ground state of formaldehyde (methanal), H 2 CO, is presented. In Section 2, properties related to the potential surface are discussed, such as equilibrium geometry, rotational and vibrational constants, infrared and Raman intensities, and dissociation and isomerization energies. In Section 3 dipole and multipole moments, polarizabilities and electric field gradients at the nuclei are covered. Finally, in Section 4, magnetic properties are reviewed, beginning with magnetizabilities and also covering rotational g -factors, NMR shielding constants and shielding anisotropies, nuclear shielding polarizabilities and hyperpolarizabilities, spin rotation constants and spin-spin coupling constants.

Ground and low-lying valence states of BN: A CI study

Abstract Using double-zeta basis sets with polarization functions, potential curves for 23 valence states of BN ( 13 Σ + , 13 Σ − , 13 π and 13 Δ states) were obtained by MRD CI methods. All states were found to be stable or metastable. Spectroscopic constants are given. 1 3 π has been confirmed to be the ground state of BN, lower in energy than 1 1 Σ + by only 0.10 eV. The equilibrium distance for 1 3 π and 2 3 π disagrees with experimental values, which are considered to be approximate only. Comparison with spectroscopic constants of C 2 , CN + and BeO shows many similarities.

STABILITY, PROPERTIES AND ELECTRONIC G-TENSORS OF H2CO- AS STABILIZED IN H2CO . NA COMPLEXES

Abstract Using HF and MP methods with high-level basis sets, the geometries, frequencies, electric dipole moments, electric field gradients, Fermi contact terms and other properties were calculated for three isomers of the H2CO·Na complex. Isomers I and II are ion-pair complexes of type H2CO−Na+, whereas III is of van der Waals type. The H2CO− moiety in isomers I and II is confirmed to be nonplanar. Isomer III is the most stable one, although energy differences between the isomers are very small (some less than 1 kcal/mol). The electron-spin magnetic moments (g-tensors) were calculated both by ROHF and multireference CI methods. Various basis sets and several gauge origins were used. The gauge dependence is small. At the ROHF level, Δgav in ppm (Δg=g−ge) is about 1300 for I, 800 for II, and −200 for III. Correlated values are expected to ∼400 ppm higher for isomer I and ∼250 ppm for isomer II. The large second-order contributions to Δg of I and II result mainly from the σ→π* and n→π* states, which are highly excited states of the complexes. Experimental studies on H2CO− in aqueous solution find Δgav=1400–1600 ppm, in good agreement with our results.

Theoretical studies on excited states of Ne2. I. MRD‐CI potential energy curves

Using a 5s3p contracted Gaussian basis with d‐polarization functions and 3s, 4s, 3p, and 4p diffuse functions, potential energy curves for excited states of Ne2 dissociating to Ne+Ne* (3s,3p,4s) were calculated by the MRD‐CI method. Five singlet and triplet states each of Σ+g Σ+u, Πg, and Πu type, and one singlet and triplet state of Δg and Δu type were considered. The features of the potential curves are discussed and compared with those obtained by previous workers.

Configuration-interaction studies on the ground state and excited states of B2

Using a 5s3p contracted Gaussian basis set, with additional d-polarization, s, p, d diffuse and p negative-ion functions, configuration-interaction (CI) methods were applied to the ground state and 55 low-lying states of B2. From the potential curves spectroscopic constants for 53 stable states were obtained. Experimentally, only the 23 Sigma -u-X 3 Sigma -g system is known. Agreement of calculated with experimental values for the two known states is very good. All-electron CI studies were performed for the two low-lying states X 3 Sigma -g and 15 Sigma -u, which are separated by only about 0.14 eV.