Pierluigi Riani

Calculation of some electronic excited states of formaldehyde

The optimized MOs of several excited states of formaldehyde have been calculated by means of a large basis set of modified Gaussian functions; particular attention has been paid to the π → π* transition. The total energy of the various states has been obtained as the sum of the SCF and correlation energies; the last one has been calculated as a functional of the electronic density. The calculated values for the transition energies are in good agreement with the experiment. A strong interaction of the π → π* state with the continuum is evidentiated; this fact can justify the absence of the π → π* band in the absorption spectrum.

V-N vertical transition of planar ethylene

The V-N vertical transition of planar ethylene has been investigated by means of a large Gaussian basis set, taking into account both the SCF and correlation energies. It is shown that in this case the SCF function, which would lead to a valuation of the Rydberg character at around 80%, does not provide an adequate description of the V state. The correlative effects bring about a lowering of the percentage of the Rydberg character to 38%. The calculated value for the transition energy is in excellent accord with the experimental data.

Theoretical study of the potential energy curves of the series of diatomic radicals MeIIX. I. Method and its application to BeF radical

A method for calculating potential energy curves of some low lying states of the diatomic radicals MeIIX (MeII = second group metal, X = halogen) is outlined. Because of the electronic structure of these compounds, applications to electronic transition lasers can be made. The first calculation regards the most simple example of this series, i.e. the BeF radical. The division of the procedure into separated steps allows a sure control of the quality of the results.

Ab initio calculation of some low-lying electronic excited states of methane

The energies of some low-lying electronic excited states of methane are calculated by using wave functions built up in terms of plane waves modulated by multicenter Gaussian factors. The wave functions of the various states are evaluated by a two steps iterative process. In the first step, each excited orbital is determined while keeping all other rigid; in the second, rearrangement effects are introduced. Final results are in good agreement with experimental data and allow to enhance an assignement hypothesis for the first electronic transitions.

An iterative process to calculate the SCF open shell orbitals

A method is described for calculating SCF open shell orbitals. In comparison with the coupling operator method, a greater velocity of convergency of the iterative process is obtained by taking into account not only the correct variational conditions, but also the best variations of orbitals step by step.

Molecular orbitals for excited states of atoms and molecules

A method is described for calculating SCF wavefunctions for excited electronic states of atoms and molecules. The orthogonality conditions with the ground state wavefunction and the underlying excited states wavefunctions are introduced in the SCF process in a simplified form.

Potential-energy curves of some electronic states of Na2 and Na2+

Abstract A calculation of the potential-energy curves of some electronic states of Na 2 and Na 2 + is reported. The crossing of Na 2 + X 2 Σ g + and Na 2 1 Σ g + ( 2 P- 2 P) supports the postulated laser-induced reaction Na 2 P + Na 2 P → Na 2 + + e − .

Theoretical study of the potential energy curves of the series of diatomic radicals MeIIX: II. Application to BeCl and MgF radicals

The potential energy curves of some low lying electronic states of the diatomic radicals BeCl and MgF have been calculated. The calculation has been performed according to a stepwise procedure, outlined in a previous work. The potential energy curves are very similar to those of the mercury halide radicals, the electronic transitions of which can be employed for efficient laser apparatus.

Theoretical investigation on the crossing states1∑ g + (2P−2P) and X2∑ g + of the dimers Li2, Na2, K2 and their positive ions Li 2 + , Na 2 + and K 2 +

Calculation has been made of the potential energy curves of the crossing states Me21∑g+(2P−2P) and Me2+X2∑g+, where Me = Li, Na, K. These crossings are the basis of the photodissociation occurring in alkali vapour lasers. The calculations are completelyab initio, following a group functions procedure.

Interpolation of molecular wave functions with a variable geometrical parameter

An interpolative method for calculating approximate wave functions of molecules with a variable geometrical parameter is presented. This method has been applied to diatomic molecules (variation of the internuclear distance), triatomic molecules (bond angle), and tetratomic molecules such as NH3 (H‐molecular axis angle). The interpolation is referred to the coefficients of the basis functions and to the coefficients of the configurations in the case of a many‐configuration wave function. The knowledge of the wave function at the extreme points of the interpolation and of the potential energy curve in an approximate form is needed.