Interpretation of photoelectron spectra of CoGen- (n = 4, 5) clusters by multiconfigurational RASPT2 calculations.

The low-lying electronic states CoGen-/0 (n = 4, 5) have been investigated with density functional theory and the state-of-the-art RASSCF/RASPT2 method to give assignments for the anion photoelectron spectra. The BP86 functional was employed to optimize the geometrical structures of the electronic states, while the RASSCF/RASPT2 was applied to calculate the single-point energies. With the RASSCF/RASPT2 approach, the active spaces are extended to a size of 21 orbitals for CoGe4-/0 and 24 orbitals for CoGe5-/0. The ground states of CoGe4-/0 are determined to be 3A″ and 2A″ of a trigonal bipyramidal structure in which the Co atom is situated at the equatorial corner of the bipyramid. The vertical detachment energies of the transitions from the anionic ground state to the neutral 2A″, 14A″, 2A', 24A″, 34A″, 14A', 24A', and 64A″ states are evaluated to be 2.29, 2.39, 2.60, 2.83, 3.17, 3.24, 3.47, and 4.00 eV. For the CoGe5-/0 clusters, the ground states are computed to be 1A1 and 12A2 of an octahedral structure. The vertical detachment energies of the removal of one electron from the anionic ground state to result in the 12A2, 12A1, 22A1, 12B1, 12B2, 42B1, 42B2, and 62A2 states are estimated to be 2.16, 2.79, 2.84, 3.06, 3.06, 3.59, 3.59, and 4.22 eV. All features in the photoelectron spectra of CoGe4- and CoGe5- are interpreted based on the computed electron detachment energies of the anionic ground states.

Electronic structures of NbGen -/0/+ (n = 1-3) clusters from multiconfigurational CASPT2 and density matrix renormalization group-CASPT2 calculations.

Density functional theory and multiconfigurational CASPT2 and density matrix renormalization group DMRG-CASPT2 have been employed to study the low-lying states of NbGen -/0/+ (n = 1-3) clusters. With the DMRG-CASPT2 method, the active spaces are extended to a size of 20 orbitals. For most of the states, the CASPT2 relative energies are comparable with the DMRG-CASPT2 results. The leading configuration, bond distances, vibrational frequencies, and relative energies of the low-lying states of these clusters were calculated. The ground states of these clusters were computed to be 3 Δ, 4 Φ, and 5 Φ of NbGe-/0/+ ; 3 A2 , 4 B1 , and 3 B1 of cyclic-NbGe2 -/0/+ ; and 1 A', 12 A″ and 12 A'' (2 E), and 3 A″ of tetrahedral-NbGe3 -/0/+ isomers. For NbGe cluster, our calculations proposed that the 6 ∑ is almost degenerate with the 4 Φ with the CASPT2 and DMRG-CASPT2 relative energies of 0.05 and 0.06 eV. The adiabatic detachment energies of NbGen - (n = 1-3) clusters were estimated to be 1.46, 1.55, and 2.18 eV by the CASPT2 method. The relevant detachment energies of the anionic ground state and the ionization energies of the neutral ground states are evaluated at the CASPT2 level.

Low-Lying Electronic States of FeGen-/0 (n = 1-3) Clusters Calculated with Multireference Second-Order Perturbation Theory.

The geometrical and electronic structures of the low-lying states of FeGen-/0 (n = 1-3) clusters are studied with density functional theory and state-of-the-art multiconfigurational CASSCF/CASPT2 and RASSCF/RASPT2 methods. For FeGe-/0 clusters, the CASSCF/CASPT2 results reveal that the relevant 3d, 4s, and 4d orbitals of Fe and 4p orbitals of Ge should be included into the active spaces to obtain the reliable relative energy order of the low-lying states. For FeGe2-/0 and FeGe3-/0 clusters, because the active spaces increase to a size of 17 and 20 orbitals, the CASSCF/CASPT2 calculations become very time-consuming. Therefore, the RASSCF/RASPT2 method is utilized to overcome the limitations of the active space. The accuracy of RASSCF/RASPT2 with several active spaces is calibrated based on the CASSCF/CASPT2 results. The structural parameters, vibrational frequencies, and relative energies of the ground and low-lying excited states of FeGen-/0 (n = 1-3) are reported. The electron detachment energies of the anionic clusters are provided. The computed results are employed to interpret the photoelectron spectrum of the FeGe3- cluster.

Geometric and Electronic Structures of VB40/+ Clusters and Reactivity of the Cationic Cluster with Methane from Quantum Chemical Calculations.

Quantum chemical methods have been employed to study the geometric and electronic structures of VB40/+ clusters and the mechanism of the reaction of the cationic clusters with methane. It was found that the ground states of the neutral and cationic clusters were 4A' and 3A' of a planar isomer in Cs symmetry in which vanadium atom side-on binds to the rhombic B4 moiety. The ionization energy of the neutral cluster was calculated to be 7.13 eV at the CCSD(T) level. The reaction pathways on the triplet and quintet potential energy profiles of the dehydrogenation and elimination of V+ in the reaction of VB4+ cluster with methane were established based on the BPW91 functional calculations. Both of the dehydrogenation and elimination of V+ in the reaction of VB4+ cluster with methane were initiated by the B4 moiety of the VB4+ cluster, and these two reaction channels were thermodynamically and kinetically favorable. The dehydrogenation and elimination of V+ in the reaction of VB4+ cluster with methane were exothermic processes.

Ground and Low-Lying Excited States of NbC3-/0 Clusters: Assignment of the Anion Photoelectron Spectra from Multiconfigurational Calculations.

The BP86 DFT, CCSD(T), and CASPT2 methods were employed to study the low-lying states of NbC3-/0 clusters. The anionic and neutral ground states were determined to be the 1A1 and 12A1 of the cyclic-NbC3-/0 isomers. All bands in the photoelectron spectra of the NbC3- cluster were interpreted based on electron detachment processes from the 1A1 of the cyclic-NbC3- isomer. The X, A, B, and C bands in the spectra are, respectively, ascribed to the transitions from 1A1 to the 12A1, 2B1, 22A1, and 2B2 states. The wave function of the initial 1A1 anionic state exhibits a pronounced multireference character that plays to some extent a role in the 1A1 → 12A1 and the 1A1 → 22A1 ionizations. Only the 1A1 → 2B2 transition appears as a clear one-electron detachment process. The Franck-Condon factor simulations for the 1A1 → 12A1 and 1A1 → 2B1 transitions are consistent with the observed vibrational progressions of the X and A bands in the spectra.

Spin State Energetics of VGe n -/0 (n = 5-7) Clusters and New Assignments of the Anion Photoelectron Spectra.

The geometrical structures, electron leading configurations, and relative energies of the low-lying states of VGe n -/0 (n = 5-7) clusters have been investigated with density functional theory and CASSCF/CASPT2 method. The pure GGA BP86 functional gave almost the same relative energy order for the low-lying states as the CASPT2 method. At the BP86 and CASPT2 levels, the ground states of VGe n -/0 (n = 5-7) clusters were proposed to be the 1 A1 and 2 A1 of A-VGe5 -/0 , 3 A″ and 2 A″, 2 A' (2 E2 ) of A-VGe6 -/0 , and 1 A' and 2 A' of A-VGe7 -/0 isomers. The adiabatic and vertical detachment energies (ADEs and VDEs) of the detachments of one electron from several orbitals of the anionic ground states were reported at the CASPT2 level. The calculated ADEs and VDEs corresponded well with the experimental values as observed in the 266 nm anion photoelectron spectra. © 2018 Wiley Periodicals, Inc.

The Electronic Structures of CoGe n-/0 ( n = 1-3) Clusters from Multiconfigurational CASSCF/CASPT2 and RASSCF/RASPT2 Calculations.

Density functional theory and multiconfigurational CASPT2 and RASPT2 methods are employed to investigate the low-lying states of CoGe n-/0 ( n = 1-3) clusters. With the RASPT2 approach, the active space is extended to 14 orbitals for CoGe-/0, 17 orbitals for CoGe2-/0, and 20 orbitals for CoGe3-/0. These active spaces include the 3d, 4s, and 4d of Co and 4p of Ge. The 4d of Co is incorporated into these active spaces in order to account for the important double-shell effect of Co. The structural parameters, vibrational frequencies, and relative energies of the low-lying states of CoGe n-/0 ( n = 1-3) are reported. The ground states of CoGe n- ( n = 1-3) are computed to be 3Φ of linear CoGe-, 3B1 of cyclic CoGe2-, and 3B1 of cyclic CoGe3- isomer. The ground states of the neutral clusters are calculated to be 2Δ of linear CoGe, 4B1 of cyclic CoGe2, and 4A″ of tetrahedral CoGe3 isomer. The calculated adiabatic and vertical detachment energies of the anionic ground states are in agreement with the experimental values as observed in the 266 nm anion photoelectron spectra.

Spin-Orbit Splittings and Low-Lying Electronic States of AuSi and AuGe: Anion Photoelectron Spectroscopy and ab Initio Calculations.

We measured the photoelectron spectra of diatomic AuSi- and AuGe- and conducted calculations on the structures and electronic properties of AuSi-/0 and AuGe-/0. The calculations at the CASSCF/CASPT2 level confirmed that experimentally observed spectra features of AuSi- and AuGe- can be attributed to the transitions from the 3Σ- anionic ground state to the 2Π (2Π1/2 and 2Π3/2), 4Σ-, 32Σ+, and 42Σ+ electronic states of their neutral counterparts. The electron affinities (EAs) of AuSi and AuGe are determined by the experiments to be 1.54 ± 0.05 and 1.51 ± 0.05 eV, respectively. The spin-orbit splittings (2Π1/2-2Π3/2) of AuSi and AuGe measured in this work are in agreement with the literature values. The energy difference between the 4Σ- (A) and 2Π1/2 states of AuSi obtained in this work is in reasonable agreement with the literature value, while that of AuGe obtained in this work by anion photoelectron spectroscopy is slightly larger than the literature value by neutral emission spectroscopy. The term energies of the 32Σ+ (B) and 42Σ+ (C) states of AuSi and AuGe were also determined based on the photoelectron spectra. Because of the different bond lengths between the anionic and neutral states, the electronic state terms energies of AuSi and AuGe estimated from the anion photoelectron spectra might be slightly different from those obtained from the neutral emission spectra.

A CASSCF/CASPT2 investigation on electron detachments from ScSi n- (n = 4-6) clusters.

In this work, the low-lying states of several isomers of ScSi n-/0 (n = 4-6) were investigated with the B3LYP functional and CASPT2 method. The ground states of the anionic clusters were predicted to be the singlet states of the trigonal bipyramid ScSi4- (A-ScSi4-), the face-capped trigonal bipyramid ScSi5- (A-ScSi5-), and the pentagonal bipyramid ScSi6- (A-ScSi6-) isomer. Based on the anionic ground states, all the relevant electron detachment processes were identified. The corresponding adiabatic and vertical detachment energies (ADEs and VDEs) of the anionic clusters were computed at the CASPT2 level. The calculated results were used to interpret all the important features in the photoelectron spectra of ScSi n- (n = 4-6) clusters. Franck-Condon factor simulations were also performed based on the B3LYP geometries, vibrational frequencies, and normal modes to explain the shapes of the first bands in the spectra.

Computational Investigation of the Geometrical and Electronic Structures of VGen-/0 (n = 1-4) Clusters by Density Functional Theory and Multiconfigurational CASSCF/CASPT2 Method.

Density functional theory and the multiconfigurational CASSCF/CASPT2 method have been employed to study the low-lying states of VGen-/0 (n = 1-4) clusters. For VGe-/0 and VGe2-/0 clusters, the relative energies and geometrical structures of the low-lying states are reported at the CASSCF/CASPT2 level. For the VGe3-/0 and VGe4-/0 clusters, the computational results show that due to the large contribution of the Hartree-Fock exact exchange, the hybrid B3LYP, B3PW91, and PBE0 functionals overestimate the energies of the high-spin states as compared to the pure GGA BP86 and PBE functionals and the CASPT2 method. On the basis of the pure GGA BP86 and PBE functionals and the CASSCF/CASPT2 results, the ground states of anionic and neutral clusters are defined, the relative energies of the excited states are computed, and the electron detachment energies of the anionic clusters are evaluated. The computational results are employed to give new assignments for all features in the photoelectron spectra of VGe3- and VGe4- clusters.

Quantum Chemical Study of the Low-Lying Electronic States of VSi3(-/0) Clusters and Interpretation of the Anion Photoelectron Spectrum.

The geometrical and electronic structures of VSi3(-/0) clusters have been investigated with the DFT, CCSD(T), and CASSCF/CASPT2 methods. The results showed that the suitable functional to identify the ground states of VSi3(-/0) clusters is not the B3LYP but the BP86. At the BP86, CCSD(T), and CASPT2 levels, the ground state of the anionic cluster was the (1)A' ((1)A1) of tetrahedral η(3)-(Si3)V(-) isomer, while that of the neutral cluster was the 1(2)A' and 1(2)A″ (1(2)E) of the same isomer. The 1(2)A' and 1(2)A″ of the tetrahedral η(3)-(Si3)V isomer were the results of the Jahn-Teller distortions of the 1(2)E in C3v symmetry. All three bands in the photoelectron spectrum of the VSi3(-) cluster were interpreted by one-electron detachments from the (1)A' anionic ground state on the basis of the BP86, CCSD(T), and CASPT2 methods. The calculated adiabatic and vertical detachment energies were in agreement with the experimental values. The broad shape of the first band was explained by Franck-Condon factor simulations for the (1)A' → 1(2)A' and (1)A' → 1(2)A″ transitions within the tetrahedral η(3)-(Si3)V(-/0) isomers.

Quantum chemical study of the geometrical and electronic structures of ScSi3 (-/0) clusters and assignment of the anion photoelectron spectra.

The geometrical and electronic structures of ScSi3 (-/0) clusters have been studied with the B3LYP, CCSD(T), and CASPT2 methods. The ground state of the anionic cluster was evaluated to be the (1)A1 of rhombic η(2)-(Si3)Sc(-) isomer, whereas that of the neutral cluster was computed to be the (2)A1 of the same isomer. All features in the 266 and 193 nm photoelectron spectra of ScSi3 (-) cluster were interpreted by the one- and two-electron detachments from the (1)A1 of rhombic η(2)-(Si3)Sc(-) isomer. The Franck-Condon factor simulation results show that the first broad band starting at 1.78 eV in the spectra comprises several vibrational progression peaks of two totally symmetric modes with the corresponding frequencies of 296 and 354 cm(-1).

Geometrical and Electronic Structures of MnS3(-/0) Clusters from Computational Chemistry and Photoelectron Spectroscopy.

The B3LYP functional and CASPT2 method have been applied to investigate the geometrical and electronic structures of η(2)-(S2)MnS(-/0), η(2)-(S3)Mn(-/0), and MnS3(-/0) isomers of MnS3(-/0) clusters. The ground state of the anionic cluster is computed to be the (5)B2 of η(2)-(S2)MnS(-) isomer, whereas that of the anionic cluster is calculated to be the (4)B1 of the same isomer. The photoelectron spectrum of MnS3(-) cluster is interpreted by electron detachment processes from the most stable η(2)-(S2)MnS(-) and from the metastable η(2)-(S3)Mn(-) and MnS3(-) isomers. The first and second bands with low intensities are, respectively, attributed to the (7)A' → (6)A' and (7)A' → (8)A' transitions within the η(2)-(S3)Mn(-/0) isomers. The third band with the highest intensity in the spectrum can be assigned to the (5)B2 → (4)B1, (5)B2 → (6)B1, and (5)B2 → (4)A2 transitions within the most stable η(2)-(S2)MnS(-/0) isomers, the (3)B1 → (2)A1 transition within the metastable MnS3(-/0) isomers, and the (7)A' → 3(6)A' transition within the metastable η(2)-(S3)Mn(-/0) isomers. Because the η(2)-(S2)MnS(-) is computed to be the most stable isomer of the MnS3(-) cluster, we believe that the highest intensity third band in the spectrum is mainly the result of electron detachments from this isomer.

Functionalization of fullerene via the Bingel reaction with α-chlorocarbanions: an ONIOM approach.

Two-layer ONIOM method at the ONIOM(B3LYP/6-31G(d):PM6) level of theory was applied to study the cycloaddition reaction of α-chlorocarbanions (CR2Cl(─), where R is H, Cl, CH3 CN, and NO2) and fullerene. The results show that the reaction pathways depend on the electron withdrawing functional groups or the electron donating functional groups contained in the α-chlorocarbanions. The energy profile analysis reveals that functionalization of fullerene by CCl3 (─), C(CH3)2Cl(─), and CH2Cl(─) is more favorable than by C(CN)2Cl(─) and C(NO2)2Cl(─) in terms of the thermodynamic point of view.

Geometric and Electronic Structures for MnS2(-/0) Clusters by Interpreting the Anion Photoelectron Spectrum with Quantum Chemical Calculations.

Geometric and electronic structures of linear SMnS, cyclic η(2)-MnS2, and linear η(1)-MnS2 isomers of MnS2(-) clusters have been investigated with B3LYP, CCSD(T), and NEVPT2 methods. The ground state of the anionic cluster is determined as (5)Πg of the linear SMnS(-) isomer, while the ground state of the neutral cluster may be either the (4)Σg(-) of the same isomer or the (6)A1 of the η(2)-MnS2 cluster. The experimental photoelectron spectrum of the MnS2(-) cluster is interpreted by contributions of these two isomers. The high-intensity band at a binding energy of 2.94 eV is attributed to the (5)Πg → (4)Σg(-) transition between the linear SMnS(-/0) clusters. The lower energy feature in the spectrum at binding energies between 1.9 and 2.8 eV and exhibiting a low intensity, is ascribed to electron detachments within the less stable η(2)-MnS2(-/0) clusters. Ionizations from the lowest energy (7)A1 state of this isomer to the neutral (6)A1, (6)A2, (8)A2, and (6)B2 states are responsible for this part of the spectrum. The extreme low intensity part between 1.3 and 1.9 eV can be due to excited states of either SMnS(-) or η(2)-MnS2(-).