Martha C. Daza

Basis set superposition error-counterpoise corrected potential energy surfaces. Application to hydrogen peroxide⋯X (X=F−, Cl−,Br−, Li+, Na+) complexes

Mo/ller–Plesset (MP2) and Becke-3-Lee-Yang-Parr (B3LYP) calculations have been used to compare the geometrical parameters, hydrogen-bonding properties, vibrational frequencies and relative energies for several X− and X+ hydrogen peroxide complexes. The geometries and interaction energies were corrected for the basis set superposition error (BSSE) in all the complexes (1–5), using the full counterpoise method, yielding small BSSE values for the 6-311+G(3df,2p) basis set used. The interaction energies calculated ranged from medium to strong hydrogen-bonding systems (1–3) and strong electrostatic interactions (4 and 5). The molecular interactions have been characterized using the atoms in molecules theory (AIM), and by the analysis of the vibrational frequencies. The minima on the BSSE-counterpoise corrected potential-energy surface (PES) have been determined as described by S. Simon, M. Duran, and J. J. Dannenberg, and the results were compared with the uncorrected PES.

Photophysics of phenalenone: quantum-mechanical investigation of singlet–triplet intersystem crossing

We have examined the electronic and molecular structure of 1H-phenalen-1-one (phenalenone) in the electronic ground state and in the lowest excited states, as well as intersystem crossing. The electronic structure was calculated using a combination of density functional theory and multi-reference configuration interaction. Intersystem crossing rates were determined using Fermis golden rule and taking direct and vibronic spin-orbit coupling into account. The required spin-orbit matrix elements were obtained applying a non-empirical spin-orbit mean-field approximation. Our calculated electronic energies are in good agreement with experimental data. We find the lowest excited singlet states to be of the npi* (S1) and pipi* (S2) type. Energetically accessible from S1 are two triplet states of the pipi* (T1) and npi* (T2) type, the latter being nearly degenerate to S1. This ordering of states is retained when the molecular structure in the electronically excited states is relaxed. We expect very efficient intersystem crossing between S1 and T1. Our calculated intersystem crossing rate is approximately 2 x 10(10) s(-1), which is in excellent agreement with the experimental value of 3.45 x 10(10) s(-1). Our estimated phosphorescence and fluorescence rates are many orders of magnitude smaller. Our results are in agreement with the experimentally observed behavior of phenalenone, including the high efficiency of 1O2 production.

Structure and bonding of H2O2···X complexes with (X=NO+, CN−, HCN, HNC, CO)

Accurate B3LYP and MP2 theoretical calculations, with the 6-311+G(3df,2p) basis set, have been performed on different complexes, between hydrogen peroxide (HP) and NO+ (1), CN− (2–4), HCN (5–8), HNC (9–12) and CO (13 and 14). According to the binding energy obtained, the charged complexes (1–4) have large binding-energy values, yielding only cyclic stationary points. However, the neutral complexes (5–14) showed medium to small binding-energy values with linear and cyclic arrangements, the cyclic structures being transition states and the linear complexes minima, on their corresponding PESs. The “atoms in molecules” theory (AIM) was used to characterize the intermolecular interactions, ranging from electrostatic interactions for the HP···NO+ complex (1) to different types of hydrogen bonding for 2 to 14. For all the structures, the binding energy was corrected for the BSSE by the counterpoise (CP) method. Moreover, calculations were performed also on the BSSE-corrected PESs.