Using Fourier-transform ion cyclotron resonance mass spectrometry, it was experimentally determin... more Using Fourier-transform ion cyclotron resonance mass spectrometry, it was experimentally determined that Sc + in the highly diluted gas phase reacts with SO 2 to form ScO + and SO. By 18 O labeling, ScO + was shown to play the role of a catalyst when further reacting with SO 2 in a Mars-van Krevelen-like oxygen exchange process. High-level quantum chemical calculations confirmed that the multi-step process to form ScO + and SO is exoergic and kinetically favored. The reaction starts from the triplet surface and although three spin-crossing points with minimal energy have been identified by computational means, there is no evidence that a two-state scenario is involved in the course of the reaction, by which the reactants could switch from the triplet to the singlet surface and back. Pivotal to the oxygen exchange reaction of ScO + with SO 2 is the occurrence of a highly symmetric four-membered cyclic intermediate by which two oxygen atoms become equivalent.
The dissociation energy of the Ti(OH2)+ ion–molecule complex was calculated by the multiconfigura... more The dissociation energy of the Ti(OH2)+ ion–molecule complex was calculated by the multiconfigurational self-consistent field theory, coupled cluster theory, and two density functional theory based methods, using both all-electron basis sets and effective core potentials. The calculations show that approximate density functional theory gives results in better agreement with experiment than either the multiconfigurational self-consistent field theory or the coupled cluster theory, with both all-electron basis sets and effective core potentials. Nevertheless, the optimized geometries and harmonic vibration frequencies are very similar, irrespective of the level of theory used. The interconfigurational energy ordering of the two valence electronic configurations dn−1s and dn−2s2 of the 4F electronic state of the titanium cation were also calculated and are discussed. Key words: ab initio, dissociation energy, ion–molecule complex, effective core potentials, transition metals.
Recently, plasmonic resonances in molecules, clusters, and nanostructures have gathered a lot of ... more Recently, plasmonic resonances in molecules, clusters, and nanostructures have gathered a lot of attention for their potential range of applicability. Unlike other metal nanostructures, a wide variety of aluminum nanostructures show very promising plasmonic properties. Theoretical and computational investigations helped to understand the nature of collective excitations in such finite systems. However, such theoretical investigations are based on qualitative approaches rather than accurate quantitative methods. In the present work, the collectivity of the low-lying states of Al13– are investigated within the time-dependent density functional theory and analyzed through different computational tools. A novel tool, which provides a quantitative index of the collective nature of the electronic excitations, has been introduced, the so-called transition inverse participation ratio (TIPR) index. The obtained results suggest the presence of plasmonic-like transitions in the Al13– cluster and that these transitio...
High-level multiconfigurational self-consistent field calculations, supplemented with multiconfig... more High-level multiconfigurational self-consistent field calculations, supplemented with multiconfigurational quasi-degenerate perturbation theory ab initio calculations with the aug-cc-pVTZ basis set, demonstrate that the [E(μ-XH)]2 (E = P, As; X = N, P, As) compounds possess one planar and one butterfly-like isomer. The calculations predict that for X = N, planar isomers, which bear substantial biradicaloid character, are more stable than their butterfly-like counterpart isomers, which feature closed-shell electronic structures. This has been ascribed to the fact that the increased bond angle strain at E-N-E is not compensated by the E-E σ (deformed) bond formation in the butterfly-like isomers, yielding the planar structures, which hold wider E-N-E bond angles, as the most stable isomers. As N is substituted by heavier atoms, either P or As, the E-P(As)-E bond angle strain is released and, additionally, as the formed E-E σ-bond is less deformed, the butterfly isomer becomes the most stable isomer. Subsequent evaluation of the normalized Giambiagi multicenter electron delocalization indices revealed no sign of electron delocalization in the four-membered rings and consequently, it is concluded that aromaticity does not play any role in the stabilization of the planar isomers.
This work presents the mechanism of the photoinduced generation of reactive oxygen species (ROS) ... more This work presents the mechanism of the photoinduced generation of reactive oxygen species (ROS) by paramagnetic copper porphyrins in aqueous solution.
The electronic structures of the lowest energy spin-states of the cationic, neutral and anionic b... more The electronic structures of the lowest energy spin-states of the cationic, neutral and anionic bare boron pentamer clusters have been investigated by means of high level multiconfigurational type calculations, in view of the large static and dynamical electron correlation effects for these species. We found that resembles a singlet spin-state perfect pentagon, which bears no intra-annular chemical bonding interactions, as shown by our analysis of the electron delocalization carried out in terms of the normalized Giambiagi ring-current index, and the total and adjacent atom-pair delocalization indices. However, its lowest-energy triplet and quintet spin-state isomers have C2v symmetry, with large intra-annular chemical bonding interactions. This geometrical feature extends to both the neutral and the anionic species. Namely, the lowest-energy isomers of boron pentamer neutral and anionic clusters have peripheral and intra-annular sizable bonding interactions reflected in the delocalization of both π- and σ-type valence natural orbitals over the whole molecular plane, which impart large structural stability. In accordance to our calculations, the lowest energy triplet spin-state isomer of the anionic boron pentamer cluster has C2 symmetry, and consequently, it should show optical activity. Finally, we have studied the change of the geometrical structure of the boron pentamer clusters from planar to compact three-dimensional structures caused by the bonding of ligands to the boron atoms. Our explicit all-electron calculations have been rationalized in terms of the shell-closure of the delocalized valence orbitals of the clusters as predicted by the jellium model extended to nonspherical confinement potentials, circumscribing the role of the ligand to modulate the total number of valence electrons assigned to the core cluster.
Using Fourier-transform ion cyclotron resonance mass spectrometry, it was experimentally determin... more Using Fourier-transform ion cyclotron resonance mass spectrometry, it was experimentally determined that Sc + in the highly diluted gas phase reacts with SO 2 to form ScO + and SO. By 18 O labeling, ScO + was shown to play the role of a catalyst when further reacting with SO 2 in a Mars-van Krevelen-like oxygen exchange process. High-level quantum chemical calculations confirmed that the multi-step process to form ScO + and SO is exoergic and kinetically favored. The reaction starts from the triplet surface and although three spin-crossing points with minimal energy have been identified by computational means, there is no evidence that a two-state scenario is involved in the course of the reaction, by which the reactants could switch from the triplet to the singlet surface and back. Pivotal to the oxygen exchange reaction of ScO + with SO 2 is the occurrence of a highly symmetric four-membered cyclic intermediate by which two oxygen atoms become equivalent.
The dissociation energy of the Ti(OH2)+ ion–molecule complex was calculated by the multiconfigura... more The dissociation energy of the Ti(OH2)+ ion–molecule complex was calculated by the multiconfigurational self-consistent field theory, coupled cluster theory, and two density functional theory based methods, using both all-electron basis sets and effective core potentials. The calculations show that approximate density functional theory gives results in better agreement with experiment than either the multiconfigurational self-consistent field theory or the coupled cluster theory, with both all-electron basis sets and effective core potentials. Nevertheless, the optimized geometries and harmonic vibration frequencies are very similar, irrespective of the level of theory used. The interconfigurational energy ordering of the two valence electronic configurations dn−1s and dn−2s2 of the 4F electronic state of the titanium cation were also calculated and are discussed. Key words: ab initio, dissociation energy, ion–molecule complex, effective core potentials, transition metals.
Recently, plasmonic resonances in molecules, clusters, and nanostructures have gathered a lot of ... more Recently, plasmonic resonances in molecules, clusters, and nanostructures have gathered a lot of attention for their potential range of applicability. Unlike other metal nanostructures, a wide variety of aluminum nanostructures show very promising plasmonic properties. Theoretical and computational investigations helped to understand the nature of collective excitations in such finite systems. However, such theoretical investigations are based on qualitative approaches rather than accurate quantitative methods. In the present work, the collectivity of the low-lying states of Al13– are investigated within the time-dependent density functional theory and analyzed through different computational tools. A novel tool, which provides a quantitative index of the collective nature of the electronic excitations, has been introduced, the so-called transition inverse participation ratio (TIPR) index. The obtained results suggest the presence of plasmonic-like transitions in the Al13– cluster and that these transitio...
High-level multiconfigurational self-consistent field calculations, supplemented with multiconfig... more High-level multiconfigurational self-consistent field calculations, supplemented with multiconfigurational quasi-degenerate perturbation theory ab initio calculations with the aug-cc-pVTZ basis set, demonstrate that the [E(μ-XH)]2 (E = P, As; X = N, P, As) compounds possess one planar and one butterfly-like isomer. The calculations predict that for X = N, planar isomers, which bear substantial biradicaloid character, are more stable than their butterfly-like counterpart isomers, which feature closed-shell electronic structures. This has been ascribed to the fact that the increased bond angle strain at E-N-E is not compensated by the E-E σ (deformed) bond formation in the butterfly-like isomers, yielding the planar structures, which hold wider E-N-E bond angles, as the most stable isomers. As N is substituted by heavier atoms, either P or As, the E-P(As)-E bond angle strain is released and, additionally, as the formed E-E σ-bond is less deformed, the butterfly isomer becomes the most stable isomer. Subsequent evaluation of the normalized Giambiagi multicenter electron delocalization indices revealed no sign of electron delocalization in the four-membered rings and consequently, it is concluded that aromaticity does not play any role in the stabilization of the planar isomers.
This work presents the mechanism of the photoinduced generation of reactive oxygen species (ROS) ... more This work presents the mechanism of the photoinduced generation of reactive oxygen species (ROS) by paramagnetic copper porphyrins in aqueous solution.
The electronic structures of the lowest energy spin-states of the cationic, neutral and anionic b... more The electronic structures of the lowest energy spin-states of the cationic, neutral and anionic bare boron pentamer clusters have been investigated by means of high level multiconfigurational type calculations, in view of the large static and dynamical electron correlation effects for these species. We found that resembles a singlet spin-state perfect pentagon, which bears no intra-annular chemical bonding interactions, as shown by our analysis of the electron delocalization carried out in terms of the normalized Giambiagi ring-current index, and the total and adjacent atom-pair delocalization indices. However, its lowest-energy triplet and quintet spin-state isomers have C2v symmetry, with large intra-annular chemical bonding interactions. This geometrical feature extends to both the neutral and the anionic species. Namely, the lowest-energy isomers of boron pentamer neutral and anionic clusters have peripheral and intra-annular sizable bonding interactions reflected in the delocalization of both π- and σ-type valence natural orbitals over the whole molecular plane, which impart large structural stability. In accordance to our calculations, the lowest energy triplet spin-state isomer of the anionic boron pentamer cluster has C2 symmetry, and consequently, it should show optical activity. Finally, we have studied the change of the geometrical structure of the boron pentamer clusters from planar to compact three-dimensional structures caused by the bonding of ligands to the boron atoms. Our explicit all-electron calculations have been rationalized in terms of the shell-closure of the delocalized valence orbitals of the clusters as predicted by the jellium model extended to nonspherical confinement potentials, circumscribing the role of the ligand to modulate the total number of valence electrons assigned to the core cluster.
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