Jorge Ricardo Letelier

Energy, chemical potential and hardness profiles for the rotational isomerization of HOOH, HSOH and HSSH

A theoretical study is reported of the mechanisms for internal rotation of hydrogen peroxide (HOOH), hydrogen thioperoxide (HSOH) and hydrogen persulphide (HSSH). Calculations at the ab initio HF//6-311G∗∗ and MP2//6-311G∗∗ levels show that these are gauche molecules presenting double-barrier torsional potentials. Important results have been obtained: two different isomerization mechanisms (trans and cis) have been characterized in terms of specific local interactions; the corresponding energy barriers have been classified according to through bond and through space interactions; and the principle of maximum hardness is qualitatively verified in all three molecules.

A numerical molecular potential for the umbrella inversion in ammonia

A numerical method based on a variational procedure, which allows the one-dimensional Schrodinger equation to be solved for an arbitrary potential energy function user-defined at selected mesh points, is used to construct an empirical one-dimensional vibrational potential for the double-well umbrella inversion problem in NH3 and its isotopically substituted molecules. The empirical potential is constructed by matching the calculated transitions to the data provided by the experimental vibrational level pattern.

Theoretical ro-vibrational spectrum of CF(+).

We determined the energies for ro-vibrational transitions of fluoromethylidynium (CF(+)) using a numerical variational approach and a Potential Energy Function calculated with the internally contracted multireference configuration interaction method including also the Davidson correction (MRCI+Q). For this purpose, all the CSFs built the full valence space have been selected as multireferential space and all the valence electrons have been correlated for the ground state X(1) summation operator(+) of CF(+). The rotational transitions observed experimentally toward the Orion Bar have been calculated to be 101.2 (102.6)GHz, 202.9 (205.2) GHz and 304.0 (307.7)GHz (experimental values in parentheses) respectively for the J=1-->0, J=2-->1 and J=3-->2 transitions. From the manifold of transitions data, it is shown how to calculate the spectroscopic parameters as well as the coefficients for the Dunham expansion.

Ab initio characterization of linear C3Si isomers

Aims. This paper presents an ab initio characterization of linear isomers of C3Si, which are suitable species for astrophysical detection in carbon-rich sources. Methods. By the help of multiconfigurational calculations, two linear minima are characterized, namely l-SiCCC and l-CSiCC, whose relative energy is 3.3 eV, and their electronic ground states have X 3 Σ − symmetry, and their electronic spectra present a high density of electronic states at low energy. Anharmonic spectroscopic parameters are predicted for both isomers and for different isotopomers using second order perturbation theory and force fields derived form 6D-potential energy surfaces. Results. The fundamental frequencies of the IR active bendings are predicted to lie around 434 cm –1 and 169 cm –1 for l-SiCCC. The rotational constants (Be) are computed to be 2753.16 MHz for l-SiCCC and 3205.37 MHz for l-CSiCC. For l-SiCCC, a relatively large spin-spin constant (λ = −0.605 cm –1 ) arises from the interaction between the ground X 3 Σ − and the lowest 1 Σ + excited state, located at 0.46 eV, resulting in complex vibrational IR-band shapes, at least, when the low- frequency bendings are excited.

Valence Orbital Ionization Energies for Second-Row Transition Elements

Valence Orbital Ionization Energies (VOIEs) are computed from Average Configuration Energies for the elements Sr through to In. VOIEs for a specific configuration are given in the form VOIE (q) = C2q2 + C1q + C0 where q is the atomic excess charge.

A variational-numerical method to solve the one-dimensional wave equation for an arbitrary potential☆

Abstract A method that is a combination of variational calculation and numerical integration is proposed to solve the Schrodinger equation. The method produces exact solutions and is not bound to any particular numerical integration algorithm.

Theory of one-dimension rotational isomerization: A study of thecis-trans isomerization of HS-NS compared to that of HO-NO

A theoretical approach, in which the potential functions representing rotational isomerization processes are expressed in terms of linear combinations of local potentials, is presented. Partitioning the torsional potential allows identification of specific contributions that are at the origin of the shape of potential curves at different regions along the torsional variable. Key properties, such as barrier heights, may then be expressed parametrically in terms of properties associated to the stable conformations. Simple analytical expressions intended to explore, quantitatively and qualitatively, the main characteristics of the transition states connecting stable isomers are formulated. As a first step towards the study of complex systems, we use this procedure to analyseab initio results concerning thecis-trans isomerization reaction of two simple prototype molecules: HSNS and HONO. We determine the relative stabilities of the different isomers and molecular structures and evaluate the associated potential barriers. It is shown that the mathematical procedure used to get potential functions is quite convenient and may be applied to the study of more complex isomerization reactions. Numerical results concerning molecular structures, potential barriers, ionization potentials and dipole moments are discussed. Comparing the values for barrier heights suggests that S(O)-S(O) π bonding through the mechanism of hyperconjugation may be present, to some extent, especially in HSNS.

On the theory of radiative transitions in centrosymmetric complexes

The theory of radiative transitions, in centrosymmetric complexes, is examined in great detail, within the framework of the crystal field method.In connection with radiative transitions, the current method of calculations, with and without invoking closure approximation, are considered from a purely theoretical point of view, by taking advantage of the irreducible tensor method put forward by Griffith.Explicit equations are derived throughout the course of this work to account for the vibronic electric dipole moments, associated with d-d and f-f type of excitations.

Vibronic Extended Hückel Theory And The Forces In Molecules

A method is presented that allows the computation of the forces acting on the atoms in a molecule along each of the symmetry nuclear displacements coordinates. The method works within the Extended Huckel formalism and makes use of the standard output of a charge-iterated calculation. In this work, examples are given of the different contributions to the total force, arising from the populated molecular orbitals, that act on the atoms in several diatomic molecules and the shape of the vibrational potential is analyzed. Also, the distortions (Peierls) that take place in a linear triatomic system of hydrogen atoms is also examined under this viewpoint.

Vibronic intensities in the electronic spectra of transition-metal complex ions

The vibronic intensities of the vibronic origins due to the three odd-parity vibrational modes of the Γ8(2T2g) → Γ8(4A2g) electronic transition of the ReBr2- 6 ion are calculated using both crystal-field and ligand-polarization vibronic models. The crystal-field calculations is carried out using the closure approximation, and both models employ the double-group formalism. The vibronic intensity distribution is different for the two models, but by using reasonable values of the radial integrals and atomic charges, satisfactory agreement with experiment is achieved.