Gabriel L. C. de Souza

We present a study of the structures and ionization energies (IEs) of a series of conformations of hydrogen peroxide (H₂O₂) dimers. Ground-state properties were computed using the coupled-cluster with single, double, and perturbative triple excitations, CCSD(T), method with large correlation-consistent basis sets, while the ten lowest-lying IEs of the H₂O₂ dimer conformations were determined through the use of the equation-of-motion ionization potential coupled-cluster with single and double excitations method (EOMIP-CCSD) combined with correlation-consistent basis sets, extrapolation to the complete basis set limit, and consideration of core-correlation effects. All of the stable conformations were determined to be within 10 kJ/mol of the most stable structure (conformation I). The first IE of conformation I was determined to be 11.72 eV, while the corresponding value for conformation V was calculated as 11.58 eV. This difference (which was also noticed for other low-lying IEs and conformations) may be helpful for the assignments of experimental results. Given that the H₂O₂ clusters were first isolated through the use of beam experiments in the recent years, it is expected that the present work can call the attention of the community. In addition, the use of the combined theoretical approaches employed regarding the selection of the relevant conformations and the exploration of the corresponding ionization processes for the molecular clusters may present an initial guide for researchers venturing into the field.

An experimental and theoretical investigation of acetaldehyde’s photoabsorption and photoionization in the vacuum-ultraviolet energy range is presented. The absorption cross sections and the ionization efficiency were measured using a double-ion-chamber spectrometer in the 10.8–21.4 eV and 13.5–21.4 eV ranges, respectively. No previous reports of these quantities were found in the literature in this energy range. Photoionization and neutral-decay cross sections were derived from these results. Theoretical calculations were performed using the Padé approximant technique and the single-center partial-wave expansion method, which were applied to solve the Lippmann–Schwinger equation to obtain the asymmetry parameters and the photoionization cross sections for the seven outermost valence orbitals. The calculations were performed in the energy range from near-threshold to 35 eV at static-exchange and static-exchange-polarization levels of approximation. Our results are contextualized with recent studies on dissociative photoionization channels and high-resolution photoelectron spectra, enabling correlations with ionic fragmentation pathways. Our experimental and theoretical results were compared between each other and with previous results from the literature, exhibiting good agreement with the available data and providing a comprehensive data set essential for modeling photochemical processes in atmospheric and astrophysical environments.

In this work, we present a systematic investigation of the ground- and excited states of six sulfonated azo dyes with broad applications in the textile industry: Allura Red, Amaranth, Carmoisine, Ponceau, Red 2G, and Sunset Yellow. Ground-state properties were evaluated using density functional theory (DFT) at the ωB97X-D4/ma-def2-SVP level of theory. To identify the most suitable functional for excited-state calculations and to assess vertical excitation energies to low-lying excited states, we tested a series of hybrid, meta-hybrid, and range-separated hybrid functionals from Jacob’s ladder using the Tamm-Dancoff approximation (TDA) and the ma-def2-SVP basis set and compared to results from RI-CC2 and STEOM-DLPNO-CCSD approaches. Excited-state properties were then further examined using TDA at the CAM-B3LYP//ωB97X-D4/ma-def2-SVP level of theory. Additionally, the quantum theory of atoms in molecules (QTAIM) was applied to explore density-related properties in both ground and excited states. We found, perhaps not surprisingly, that excitation weakens the N−−N bond in both the enol and keto forms of the dyes, but with variations depending on the molecule, conformer, and electronic state. This bond weakening, as reflected by changes in electron density descriptors, suggests a possible route for photodegradation in aquatic environments.

In this work, we performed an investigation on the structures and ionization potentials (IPs) of the H₂CO⋯HNO dimer.

In this work, properties related to antioxidant-potential mechanisms (such as the bond dissociation enthalpy, BDE, for the homolytic cleavage of the O-H bond and ionization energies, IEs) were determined for phenol, pyrocatechol, and gallic acid (GA). Both the protonated and deprotonated forms of GA were investigated. The Feller-Peterson-Dixon (FPD) composite method was employed with a variety of computational approaches, i.e., density functional theory, Möller-Plesset perturbation theory, and coupled-cluster-based methods, in combination with large correlation consistent basis sets with extrapolation to the complete basis set limit and consideration of core electron correlation effects. FPD results were compared to experimental and computational data available in the literature, presenting good agreement. For example, the FPD BDE (298 K) obtained for phenol, which was based on valence-correlated MP2/CBS calculations with contributions from correlating all electrons, was determined to be 87.56 kcal/mol, a value that is 0.42 kcal/mol lower than the result obtained in the most recent experiments, 87.98 ± 0.62. Calibration against coupled-cluster calculations was also carried out for phenol. We expect that the outcomes gathered here may help in establishing a general protocol for computational chemists that are interested in determining antioxidant-related properties for phenolic compounds with considerable accuracy as well as to motivate future IE measurements (particularly for GA) to be accomplished in the near future.