Hans Suter

A theoretical study on the internal rotation and hyperfine structures of the ethyl radical (CH3-CH2)

Abstract It is confirmed by the UMP2/6-31G** level of calculation, that the zero-point vibrational energy dominates in determining the conformational preference and the extremely low barrier to internal rotation in the ethyl radical. The isotropic hyperfine coupling constants of hydrogens and carbons of the ethyl radical have been calculated using an extended ab initio single- or multi-reference CI wavefunction (SR-CI or MR-CI). The spin density at each nucleus of interest has been calculated as a function of the basis sets and the CI-dimensions. The influence of the internal rotation of the methyl group and the inversion of the methylene group on the hyperfine coupling constants has also been studied. Furthermore, the anisotropic hyperfine coupling constants (dipolar term) have been calculated and compared with available experimental values.

Ab initio quantum-chemical study of the lower-lying electronic states of o-benzyne

Abstract The lower-lying singlet and triplet states of o-benzyne (C6H4) have been calculated by ab initio methods such as CASSCF, CASPT2, MR-CISD and MR-ACPF schemes employing an ANO basis set as well as the CIS method. The calculated results are compared with a recent electronic absorption spectrum of transient o-benzyne in an Ar matrix and with negative ion photoelectron spectroscopy. It is shown that the dipole-allowed lowest singlet excitation is the 1B1 (πσ*) ←1A1 and the lowest triplet state is the 3B2(σσ*) state with calculated vertical energies of 4.0 and 2.0 eV, respectively. The calculated dipole moments are also reported.

IS ACETYLENE RADICAL ANION WITH A TRANS-BENT FORM OBSERVED IN MATRIX EXPERIMENT ? AN AB INITIO STUDY

Based on extensive ab initio calculations of the hyperfine coupling constants of both hydrogen and carbon nuclei of three C2H−2 anions, it is confirmed that an acetylene radical anion has effectively been produced radiolytically in low temperature alkane matrices and it possesses a trans‐bent form. The results are derived from different molecular orbital configuration interaction calculations (CIS, CISD, QCISD and MRD‐CI) as well as density functional theory (DFT) employing extended basis sets. Both popular DFT methods (BLYP and B3LYP) show some difficulties in calculating the isotropic coupling constants of the carbon nuclei.

An ab initio calculation of the vertical excitation energies of naphthalene

Abstract The lower lying singlet and triplet states of naphthalene (C10H8) have been calculated by ab initio methods such as CIS, CASSCF, and CASPT2 schemes employing the correlation consistent DZP basis set. The calculated results are compared with those obtained from a recent spectroscopic study and with other previous theoretical studies. The lowest lying triplet state (3Bu) is calculated at about 3.0 eV above the singlet ground state (1Ag) and the first singlet-singlet excitation (1B3u ← 1Ag) is calculated at around 3.6eV.

Photodissociation dynamics of HNF. I. Ab initio calculation of global potential energy surfaces, vibrational energies, and wave functions

Three-dimensional potential energy surfaces for the X 2A″ and A 2A′ states of HNF are reported in the present paper. The ab initio calculations are carried out at the multireference configuration interaction (MRD–CI) level of theory employing a large basis set. The X 2A″ potential surface possesses a deep potential well. Both surfaces have a bent equilibrium, at approximately 100 deg for the ground state and at about 125 deg for the excited one. The two electronic states become degenerate at the linear geometry. Variational calculations for the vibrational energies and the corresponding wave functions have been performed on three-dimensional fitted potential energy surfaces. The first 101 levels of the X 2A″ state and the lowest 51 levels of the A 2A′ manifold are reported, and their vibrational modes are assigned on the basis of the nodal structure of the corresponding wave functions. The A 2A′ vibrational states consist of well-defined polyads with polyad quantum number P=3ν1+ν2+ν3, where ν1−ν3 are t...