Edilson C. da Silva

Theoretical characterization of the ground state of the alkaline-earth monocarbides: Ordering of the two lower-lying states of the BeC, MgC, and CaC molecules

The two lower-lying electronic states (3Σ− and 5Σ−) of the BeC, MgC, and CaC molecules were investigated using restricted Hartree-Fock (RHF), generalized valence bond (GVB), and configuration interaction (CI) calculations to establish the relative ordering of those states as a function of the size of the alkaline-earth element. It is shown that as a result of the competition between bonding effects, which predominate for the 3Σ− states, and exchange effects, which stabilize the 5Σ− states, the ordering of these states can be reversed as we move from the Be to the Ca atom. For both the BeC and MgC molecules, the ground state was found to be a triplet X3Σ− state, but for the CaC molecule, the high-spin X5Σ− becomes more stable.

Unimolecular reactions on formaldehyde S0 PES

Abstract The competitive unimolecular reactions of formaldehyde, H 2 CO→H 2 +CO; H 2 CO→ trans -HCOH and H 2 CO→H+HCO, were comparatively studied under the direct dynamics formalism, using Density functional and ab initio levels of theory. In addition, the geometric isomerization trans -HCOH→ cis -HCOH was evaluated. Calculated reaction path properties were used in the determination of Rice–Ramsperger–Kassel–Marcus microcanonical rate coefficients. The reaction dynamics was evaluated for each individual process based on the nuclear displacements in the reaction path and normal coordinate analysis. Our results found are in very good agreement with experimental barrier heights and quantum yields trends.

AB initio and configuration interaction calculations for some σ → π* superexcited states of the trans-1,3-butadiene molecule

Abstract Some σ → π ∗ superexcited states of the trans-1,3-butadiene molcule have been calculated in order to establish them as possible candidates for the 9.52 eV and 11.04 eV transitions observed in the electron impact spectra of this molecule. Four states have been solved self-consistently ( 7a g → 2a u 2a g and 2b g and 6b u → 2a u , 2bg) and on the basis of extensive CI calculations of transition energies and oscillator strengths, we assign the 11.04 eV transition to the 1 B g (6b u → 2a u ) state. The transition observed at 9.52 eV is more likely to be either a π (la u ) → π∗ transition or the first member of a Rydberg series converging to the second ionization potential.