G. de Brouckère

Ab initio one-electron property calculations II : Molecules C3H6O, C4H6O and C3H6S

Ab initio S.C.F. molecular orbital calculations have been carried out for the molecules C3H6O, C4H6O and C3H6S and the expectation values of the following observables have been derived: electronic potential, dipole, quadrupole, octupole moments, diamagnetic susceptibility, second moments, second moment anisotropies of the charge distribution, electric field, electric field gradient, diamagnetic shielding and nuclear quadrupole coupling constant. Extended basis sets including d-type polarization functions have been used throughout. Excellent agreement with experiment is obtained.

Configuration interaction calculations of miscellaneous properties of the excited state and related transition bands of phosphorus monoxide

Abstract Extended basis set configuration interaction calculations on the excited state ( C ′ 2 Δ ) and several C ′ 2 Δ– X 2 Π r transition bands of phosphorus monoxide have been performed. A variety of molecular properties are reported including: (i) spectroscopic constants; (ii) vibrational energies of the C ′ 2 Δ -state, transition band energies of several C ′ 2 Δ– X 2 Π r bands and related Franck–Condon parameters; (iii) selected one-electron properties such as the electric multipole moments, 17 O nuclear quadrupole coupling, anisotropic hyperfine parameters, etc; (iv) vibrational electric dipole moments; (v) C ′ 2 Δ vibrational lifetimes through cascade and via electric dipolar decays C ′ 2 Δ→ X 2 Π r . Good agreement is obtained with the available limited amount of experimental data. The accuracy of the present results is discussed and compared to that obtained for the X 2 Π r -state and for excited states of homologous diatomics.

Ab initio one-electron property calculations III. Pentacyclic molecules : III. Pentacyclic molecules: C5H6, C4H5N, C4H4O, C4H4S, C4H6S

A set of ab initio SCF calculations of one-electron observables has been derived for a series of pentacyclic molecules, that is C5H6, C4H5N, C4H4O, C4H4S and C4H6S, as well as for the molecules CS and H2S. A comparison of measured and calculated properties for CS and C4H4S as well as for H2S and C4H6S shows interesting common trends. For the measured properties, that is dipole and quadrupole moments, diamagnetic susceptibilities, second moment anisotropies, the theoretical results are in quite reasonable agreement with observation throughout the series except for the dipole moment of C4H4S. The latter is shown to be very sensitive to the nature of the basis set and the theoretical discrepancy at the SCF level is demonstrated to be due to the nature of the S-C bonds in thiophene. Correlation effects are likely to be important for this observable and an estimate of these made by means of existing CI calculations on the dipole moment of CS leads to a theoretical moment for thiophene in good agreement with the measured quantity. Unmeasured one-electron properties have been derived as well for the above pentacyclic molecules, namely the potentials, electric fields, electric field gradients, nuclear quadrupole coupling constants, diamagnetic shieldings and octupole moments. The theoretical tensorial components of the nuclear quadrupole coupling constant for C4H6S are rather close to those for H2S and the latter agree quite well with their experimental counterparts.

Ab initio one-electron property calculations

A series of one-electron properties, i.e. dipole, quadrupole, octupole moments, diamagnetic susceptibility, second moments and second moment anisotropies of charge distribution, electric field, electric field gradient, diamagnetic shielding, nuclear quadrupole coupling constant, have been obtained by ab initio S.C.F. calculations for the molecules COF2, SO2F2 and SOF2. The effect of the size of the gaussian basis sets, including d-type polarization functions, as well as the contraction schemes on the latter properties have been studied for the COF2 molecule. This study enables us to determine the basis giving the best results as compared to experiment. With this basis the calculations have been extended to the properties of the molecules SO2F2 and SOF2. Good overall agreement with experiment is obtained.

Miscellaneous property computations on the X 3Σ−-state of phosphorus monofluoride by configuration interaction calculations

Abstract Extended basis set configuration interaction calculations on the ground state of phosphorus monofluoride PF( X 3 Σ − ) have been achieved. Several properties are reported, classified as follows: (i) spectroscopic constants; (ii) vibrational energies and related anharmonicity parameters; (iii) pure rotational excitations; (iv) selected one-electron properties such as electric multipole moments, anisotropic hyperfine parameters, 17 F nuclear quadrupole coupling and others; (v) vibrational dipole moments; (vi) cascade vibrational lifetimes. Good agreement is obtained with the restricted number of experimental data available. A comparison is made between the accuracy of the present results and that of analogous diatomics for which supplementary experimental data have been reported.

Molecular orbital calculations on some copper complexes

Abstract A semi-empirical MO calculation has been made on a number of copper complexes which are of interest in EPR and in quantum chemistry: CuCl 4 2− , CuCl 4 , CuCl 4 (NH 3 ) 2 . Details are given about the charge distribution, overlap populations, and sequence of orbital energies.

Configuration interaction calculations on the X1 Sigma + ground state and low-lying A1 Pi and 1 Delta excited states of the PN molecule. I. Potential energy curve of the X1 Sigma + state of PN. Miscellaneous spectroscopic observables

A series of multireference configuration interaction (CI) calculations using an extended Gaussian basis set have been performed on the X1 Sigma + ground state of the PN molecule in order to accurately determine the potential energy surface in the vicinity of the minimum. With the help of this curve a wide assortment of spectroscopic observables have been computed. The overall agreement with experiment is good. Marked correlation energy effects are found for the electric dipole/quadrupole moments and nitrogen nuclear coupling. Pure rotational excitations calculated by means of the numerical solutions of the radial Schrodinger equation are found to be in quite good agreement with experiment. Average values of the electric dipole moment over the first vibrational levels have been derived and the trend exhibited by the experimental data is well reflected by the theoretical results. Vibrorotational transitions, pure vibrational and vibrorotational lifetimes have also been determined which, to date, have not been determined experimentally.

Configuration interaction calculations on the P2 molecule. I. Potential energy curves of the X 1Sigmag+ and a 3Sigmau+ states of P2; spectroscopic properties

Extended basis set, multireference configuration interaction (CI) calculations have been performed on the ground state (X 1Sigmag+) and the lowest experimentally known excited state (a 3Sigmau+) of P2. Computed spectroscopic constants were found to be in good agreement with the available experimental data. An exception to this is the anharmonicity constant omegac chic of the excited state. The Franck-Condon factors and the pure vibrational transitions for the a 3Sigmau+ to X 1Sigmag+ transition band, which are unknown experimentally have been derived for several vibrational quantum numbers and compared with corresponding values arising from a simulated spectrum based on the use of the Klein-Dunham potential function. Pure rotational transitions within the ground and excited states, calculated for several vibrational and rotational quantum numbers, agree fairly well with the experimental data. The excited state results were found to be in somewhat closer agreement with experiment than the ground state results.

Calculation of the Fermi contact term in some transition metal complexes from unrestricted Hartree—Fock molecular orbitals

Abstract A semi-empirical unrestricted Hartree—Fock MO method has been developed for the purpose of calculating the Fermi contact term in transition metal complexes. An application to the systems CuCl 2− 4 and MnCl 2− 4 , which exist in an NH 4 Cl crystal doped with Cu 2+ or Mn 2+ , yields values which are in reasonable agreement with results derived from ESR spectra.

CI effects on one-electron properties: the case of the electric quadrupole moment of OCS

One-electron properties of the OCS molecule have been obtained from SCF and CI wavefunctions using extended Gaussian basis sets. While most properties are in good agreement with experiment, the electric quadrupole moment is an exception. The effect of additional diffuse s-, p- and d-type functions is examined. By an appropriate choice of d exponents it has been possible to obtain improved agreement with experiment for the quadrupole moment at the CI level. In particular, for the quadrupole moment of OCS: theta SCF=-5.27*10-40 Cm2 theta CI=-3.58*10-40 Cm2 as compared with theta EXP=(-2.93+or-0.50)*10-40 Cm2 experimentally.