Unveiling geometric and electronic structures of NbSi4 −/0 clusters and electron detachments of the anionic cluster: A quantum chemical investigation

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This article presents computational insights into the geometric and electronic structures of NbSi4 −/0 clusters using density functional theory and the CASSCF/CASPT2 method. The anionic and neutral ground states are identified as the 1A′ and 2A′ states, respectively, within a trigonal bipyramidal isomer where the Nb atom occupies the equatorial position. The adiabatic detachment energy for the transition from the anionic ground state 1A′ to the neutral ground state 2A′ is estimated to be 2.30 eV.

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Nội dung Text: Unveiling geometric and electronic structures of NbSi4 −/0 clusters and electron detachments of the anionic cluster: A quantum chemical investigation

Received: 17 October 2023 Revised: 4 January 2024 Accepted: 13 January 2024 DOI: 10.1002/vjch.202300355 RESEARCH ARTICLE Unveiling geometric and electronic structures of NbSi4−/0 clusters and electron detachments of the anionic cluster: A quantum chemical investigation Van Tan Tran Theoretical and Physical Chemistry Division, Dong Thap University, Dong Thap, Vietnam Abstract This article presents computational insights into the geometric and elec- Correspondence tronic structures of NbSi4 −/0 clusters using density functional theory and the Van Tan Tran, Theoretical and Physical Chemistry Division, Dong Thap University, 783-Pham Huu CASSCF/CASPT2 method. The anionic and neutral ground states are identified as Lau, Ward 6, Cao Lanh City, Dong Thap 81000, the 1 A′ and 2 A′ states, respectively, within a trigonal bipyramidal isomer where Vietnam. the Nb atom occupies the equatorial position. The adiabatic detachment energy Email: tvtan@dthu.edu.vn for the transition from the anionic ground state 1 A′ to the neutral ground state 2 A′ is estimated to be 2.30 eV. Additionally, an evaluation of the vertical detachment energies for transitions to the neutral states 12 A′, 12 A″, 22 A′, 22 A″, 32 A′, 32 A″, and 42 A′ yields respective values of 2.42, 2.78, 2.94, 3.34, 3.86, 4.08, and 4.28 eV. These computed electron detachment energies successfully account for all five bands observed in the photoelectron spectrum of the anionic cluster. Furthermore, the Franck–Condon factor simulations reveal extensive vibrational progressions asso- ciated with the transition to the neutral ground state 12 A′, manifesting as an unresolved broad band at 2.41 eV in the spectrum. KEYWORDS CASPT2, detachment energy, density functional theory, electronic state, Franck–Condon factor, geometric structure 1 INTRODUCTION NbSi4 − cluster exhibits five features with vertical detach- ment energies (VDEs) of 2.41, 2.92, 3.29, 3.80, and 4.18 eV. The structures and properties of many transition Niobium The adiabatic detachment energy (ADE) of the first band silicide films or alloys can have applications in digital super- was determined to be 2.12 eV. conducting electronics, bolometers for astrophysical parti- The geometric structures of NbSi4 −/0 clusters were inves- cle detection, and aircraft turbine engines.1–4 Investigating tigated using advanced computational methods, specifi- Nb-doped silicon clusters contributes to a deeper under- cally density functional theory (DFT) and coupled-cluster standing of the microscopic mechanisms in NbSi films CCSD(T) method.17 The findings unveiled the presence of and metal-semiconductor alloys, while providing valuable two significant isomers within the NbSi4 − cluster. Isomer 4A information for cluster-assembled material production. The exhibited a stable trigonal bipyramidal structure, with the structures and properties of a large number of niobium- Nb atom occupying the equatorial position, while isomer 4B doped silicon clusters have been investigated using both displayed a planar cyclic structure. Through energetic anal- experimental and theoretical methods.5–17 Regarding the ysis, it was determined that the 1 A state of isomer 4A is the NbSi4 −/0 clusters, the anionic clusters were synthesized and ground state, with a lower energy compared to 3 A″ state analyzed using photoelectron spectroscopy with 266 nm of isomer 4B by 0.74 eV. Additionally, when considering the wavelength photons.17 The photoelectron spectrum of neutral cluster, the calculated ground state corresponded © 2024 Vietnam Academy of Science and Technology and Wiley-VCH GmbH. Vietnam J. Chem. 2024;62:261–268. wileyonlinelibrary.com/journal/vjch 261
25728288, 2024, 2, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/vjch.202300355 by Readcube (Labtiva Inc.), Wiley Online Library on [01/05/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License 262 TRAN to the 2 A1 state of the cyclic isomer, whereas the 2 A state Franck–Condon factor simulation was conducted for the of the trigonal bipyramidal isomer was found to be ener- one-electron detachment process of the anionic cluster getically less favorable by 0.89 eV. The calculated ADE and with the MOLFC code.26,27 VDE values of the 1 A state of isomer 4A were determined To investigate the electronic states and determine the to be 2.25 and 2.39 eV, respectively, which aligned closely electron detachment energies of the lowest energy iso- with the experimental values of 2.12 and 2.41 eV. This mer, CASSCF/CASPT2 calculations were employed. The comprehensive investigation sheds light on the geometric ANO-RCC basis sets28,29 with a contraction scheme of characteristics and stability of NbSi4 −/0 clusters, provid- [8s7p5d3f2g1h] for Nb and [6s5p3d2f1g] for Si were uti- ing valuable insights into their structural properties and lized in these calculations. To account for scalar relativistic electronic behavior. effects, the Douglas–Kroll–Hess transformation of one- While the DFT and CCSD(T) calculations have provided electron integrals was applied.30,31 The IPEA shift and insights into the ground states of NbSi4 −/0 clusters, the imaginary shift in the CASPT2 calculations were set to their exploration of excited states has been overlooked. Conse- default values of 0.25 and 0.10, respectively. The CASPT2 quently, this approach has limitations in analyzing spectral calculations did not include electron correlation in the 1s, bands beyond the first one. To address these limitations, the 2s, 2p, 3s, 3p, and 3d orbitals of Nb, as well as the 1s orbital of multiconfigurational CASSCF/CASPT2 method has gained Si. All CASSCF/CASPT2 calculations were performed using recognition as a valuable technique for investigating the the OpenMolcas software.32 geometric structure and electronic states of clusters con- In the CASSCF calculations, the active space could be taining transition metals. This method has been extensively selected to include the 4d and 5s orbitals of Nb, as well as employed in the study of various clusters, such as NbC3 −/0 , the 3p orbitals of Si. The resulting active space consisted ScSin −/0 (n = 4−6), VGen −/0 (n = 1−4), and VSi4 −/0 .18–21 The of 14 or 13 electrons distributed among 18 orbitals. Since integration of theoretical and experimental approaches has the CASSCF/CASPT2 method is typically limited to active yielded promising results in utilizing the CASSCF/CASPT2 spaces of around 14 orbitals, three antibonding orbitals method to predict adiabatic detachment energy (ADE) and were excluded from the active space to ensure computa- vertical detachment energy (VDE) values. These predictions tional feasibility. As a result, the final active space contained have been found to align closely with experimental obser- 14 or 13 electrons distributed among 15 orbitals. It is vations. Moreover, this combined approach has proven worth noting that an active space consisting of around 15 valuable in providing comprehensive explanations for all orbitals has been widely recognized as sufficient for calcu- the features observed in photoelectron spectroscopy. lating the relative energies of electronic states and electron Upon reviewing the scientific literature, it was discovered detachment energies of an isomer in clusters containing that there is a lack of comprehensive studies on the geomet- transition metal elements.19–21,33 This choice strikes a bal- ric and electronic structures of NbSi4 −/0 clusters. To provide ance between computational efficiency and capturing the further detailed insights into the ground state and excited essential electronic correlation effects in these systems. states of isomers within the NbSi4 −/0 cluster, the present investigation will combine the DFT with the multiconfigura- tional CASSCF/CASPT2 method. The computational results 3 RESULTS AND DISCUSSION obtained from this analysis will enable a comparison and explanation of all features observed in the photoelectron 3.1 NbSi4 − spectrum of NbSi4 − cluster. Figure 1 displays the structures of NbSi4 − clusters obtained from geometry optimizations using the BP86 functional. 2 COMPUTATIONAL DETAILS The computational results indicate that NbSi4 − cluster has three important isomers which are called A-NbSi4 − , B- Geometry optimization and harmonic vibrational fre- NbSi4 − , and C-NbSi4 − . The A-NbSi4 − isomer has a trigonal quency calculations were conducted using DFT. The calcu- bipyramidal structure with the niobium atom located at the lations employed the BP86, PBE, B3LYP, and PBE0 function- equatorial position, the B-NbSi4 − isomer has a non-planar als and the def2-QZVP basis sets.22,23 In particular for Nb, cyclic structure, and the C-NbSi4 − isomer has a trigonal the def2-QZVP basis set includes an effective core poten- bipyramidal structure with the niobium atom located at the tial of 28 electrons.24 To explore the low-lying states of the axial position. All these three isomers exhibit Cs symmetry. studied clusters, DFT calculations were performed for vari- Table 1 summarizes the results of the BP86, PBE, B3LYP, ous spin multiplicities ranging from singlet to septet for the and PBE0 functionals and the CASPT2 calculations. One sig- anionic cluster and from doublet to sextet for the neutral nificant finding from the calculations is that all the methods cluster. All density functional calculations were executed used in this research indicate an anionic ground state of using NWCHEM 7.0.2 software.25 Subsequently, based on 1 A′ of the A-NbSi − isomer. On the other hand, the 3 A′ of 4 the geometries and vibrational normal modes obtained A-NbSi4 − , the 3 A″ of B-NbSi4 − , and the 3 A″ of C-NbSi4 − with the BP86 functional calculations, a multidimensional isomers exhibit significantly higher energies. This result
25728288, 2024, 2, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/vjch.202300355 by Readcube (Labtiva Inc.), Wiley Online Library on [01/05/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License TRAN 263 F I G U R E 1 Structures of the relevant isomers of the anionic NbSi4 − cluster obtained using the BP86 functional calculations. suggests that the B-NbSi4 − and C-NbSi4 − isomers are less in comparison to the other Nb–Si bonds within the cluster. stable than the A-NbSi4 − isomer. Furthermore, the positive Such a weak bond with an extended length can be sensitive vibrational frequencies reported for all the isomers indicate during electron removal. Otherwise, the 3 A′ state of the A- that these structures correspond to minima on the potential NbSi4 − isomer displays Nb−Si bond lengths of 2.484, 2.864, energy surface. This means that the computed geometries and 2.503 Å, along with Si−Si bond lengths of 2.506, 2.317, represent stable configurations for the NbSi4 − cluster. and 2.534 Å. Additionally, the 3 A″ electronic state of the B- The bond distances of the stable isomers of the NbSi4 − NbSi4 − isomer exhibits Nb-Si bonds of 2.451 and 2.594 Å, cluster, calculated using the BP86 functional, are illustrated and Si-Si bonds of 2.300 and 2.319 Å. Finally, the 3 A″ state in Figure 1. In the ground state 1 A′ of the A-NbSi4 − isomer, of the C-NbSi4 − isomer showcases Nb-Si bonds of 2.477 and the Nb─Si bond lengths are calculated to be 2.408, 2.879, 2.452 Å, as well as Si-Si bonds of 2.864, 2.506, 2.461, and and 2.400 Å, while the Si─Si bond lengths are 2.654, 2.374, 2.383 Å. and 2.539 Å. The corresponding Wiberg bond orders for the The calculated results obtained through the DFT and Nb–Si bonds are 2.24, 1.44, and 2.18, while the Si–Si bonds CASPT2 calculations in this work are in agreement with exhibit bond orders of 0.87, 1.41, and 1.01. It is important the findings achieved using DFT and the CCSD(T) method. to note that in the ground state 1 A′, the Nb–Si bond with a In the previous study, the calculations with the B3LYP length of 2.879 Å and a bond order of 1.44 is significantly functional and CCSD(T) method identified the 1 A state longer than the other Nb-Si bonds. This elongated Nb–Si of the A-NbSi4 − isomer as the ground state.17 Similarly, bond, with a lower bond order, suggests a weaker bond in this work, the calculations utilizing several functionals TA B L E 1 Relative energies of the electronic states of NbSi4 − obtained using the BP86, PBE, B3LYP, and PBE0 functionals and CASPT2 calculations. Relative energy (eV) Isomer State Vibrational frequency (cm−1 ) BP86 PBE B3LYP PBE0 CASPT2 A-NbSi4 − 1 A′ 41, 84, 121, 201, 304, 306, 337, 401, 415 0.00 0.00 0.00 0.00 0.00 3 A′ 106, 180, 232, 249, 288, 297, 333, 426, 428 0.69 0.67 0.66 0.56 1.09 B-NbSi4 − 3 A″ 82, 90, 178, 229, 292, 303, 388, 431, 459 0.79 0.87 0.71 0.84 1.31 C-NbSi4 − 3 A″ 174, 176, 234, 277, 308, 325, 327, 396, 455 0.72 0.68 0.82 0.65 1.13
25728288, 2024, 2, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/vjch.202300355 by Readcube (Labtiva Inc.), Wiley Online Library on [01/05/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License 264 TRAN F I G U R E 2 Molecular orbitals and electron occupations of the 1 A′ state of the A-NbSi4 − isomer obtained through CASSCF calculations with an active space consisting of 14 electrons distributed among 15 orbitals. and the CASPT2 method also determine the 1 A′ state electron from the bonding orbital 33a′ to the antibonding of the A-NbSi4 − isomer state as the ground state. These orbital 34a′. results obtained from different computational approaches demonstrate a convergence in the identification of the ground state for the A-NbSi4 − cluster. 3.2 NbSi4 Figure 2 illustrates the molecular orbitals and electron occupation numbers of the leading configuration for the Table 2 presents the relative energies of the electronic 1 A′ state of the A-NbSi − isomer, obtained through multi- 4 states for the neutral NbSi4 cluster, calculated using the configurational CASSCF calculation. The leading configura- BP86, PBE, B3LYP, B3PW91, and PBE0 functionals and the tion in the 1 A′ state of the A-NbSi4 − isomer is determined as CASPT2 method. The results indicate that the 2 A′ state of 30a′2 31a′2 32a′2 33a′2 14a″2 15a″2 16a″2 . This configuration the A-NbSi4 isomer is the ground state for the neutral clus- implies that the bonding orbitals 30a′, 31a′, 32a′, 33a′, 14a″, ter. The 2 A′ state of the C-NbSi4 isomer is slightly higher 15a″, and 16a″ are completely occupied, while the remain- in energy, with a relative energy of 0.13 eV as computed ing antibonding orbitals remain unoccupied. Furthermore, using the CASPT2 method. Additionally, the other excited the reference weight of the leading configuration in the 1A′ states are reported as the 2 A″ state of the A-NbSi4 isomer state is determined to be 80%. Additionally, the excited 3 A′ and the 2 A′ state of the B-NbSi4 isomer with CASPT2 relative state of the A-NbSi4 − isomer is achieved by exciting one energies of 0.43 and 1.05 eV.
25728288, 2024, 2, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/vjch.202300355 by Readcube (Labtiva Inc.), Wiley Online Library on [01/05/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License TRAN 265 TA B L E 2 Relative energies of the electronic states of NbSi4 obtained using the BP86, PBE, B3LYP, and PBE0 functionals and CASPT2 calculations. Relative energy (eV) Isomer State Vibrational frequency (cm−1 ) BP86 PBE B3LYP PBE0 CASPT2 A-NbSi4 2 A′ 98, 207, 221, 250, 286, 287, 372, 434, 458 0.00 0.00 0.00 0.00 0.00 2 A″ 52, 200, 200, 239, 319, 344, 350, 386, 427 0.43 0.46 0.52 0.37 0.43 B-NbSi4 2 A′ 35, 62, 154, 216, 284, 321, 402, 479, 560 0.69 0.81 0.63 0.90 1.05 C-NbSi4 2 A′ 122, 145, 221, 238, 284, 284, 293, 413, 433 0.24 0.23 0.42 0.38 0.13 Figure 3 presents the computational results displaying Nb─Si bonds in the neutral ground state. The leading con- the structures of the electronic states for the three iso- figurations of the neutral ground state 2 A′ are determined mers of the neutral NbSi4 cluster. Most of the electronic as 30a′2 31a′2 32a′2 33a′1 14a″2 15a″2 16a″2 . Comparing this states retain the structures of the corresponding anionic configuration to that of the anionic ground state 1 A′, there cluster isomers. However, the excited 2 A″ state of the A- is a deficiency of one electron in the 33a′ orbital. NbSi4 isomer slightly deviates from the trigonal bipyramidal Figure 4 shows the computed harmonic vibrational fre- structure due to the elongation of the weaker Nb─Si bond. quencies and corresponding normal modes of the neutral In the ground state 2 A′ of the A-NbSi4 isomer, the Nb-Si ground state 2 A′ of the A-NbSi4 isomer using the BP86 func- bonds exhibit lengths of 2.471, 2.678, and 2.419 Å, while the tional. These normal modes are classified and labeled as Si─Si bonds measure 2.555, 2.305, and 2.595 Å. The Wiberg A′ and A″ irreducible representations within the Cs point bond orders for the Nb─Si bonds in this doublet ground group. Within the A′ irreducible representation, there are state are estimated as 1.92, 1.60, and 2.12, while those for six normal modes that exhibit complete symmetry. These the Si-Si bonds are 0.97, 1.44, and 0.93. It is noteworthy modes possess frequencies of 98, 207, 250, 286, 372, and that the Nb─Si bond with a length of 2.678 Å and a bond 434 cm−1 . They contribute to the vibrational behavior order of 1.60 is significantly weaker compared to the other while maintaining the overall molecular symmetry of the F I G U R E 3 Structures of the relevant isomers of the neutral NbSi4 cluster obtained using the BP86 functional calculations.
25728288, 2024, 2, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/vjch.202300355 by Readcube (Labtiva Inc.), Wiley Online Library on [01/05/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License 266 TRAN F I G U R E 4 Symmetry and frequency in cm−1 of the vibrational normal modes of the 2 A′ state in the neutral A-NbSi4 isomer obtained through harmonic vibrational frequency calculation using the BP86 functional. A-NbSi4 cluster. On the other hand, the remaining three the niobium atom located at the equatorial position, is normal modes characterized by frequencies of 221, 287, identified as the most energetically stable. and 458 cm−1 fall under the A″ representation. As A″ modes, they introduce vibrational motions that disrupt the molecular symmetry of the A-NbSi4 cluster. 3.3 Electron detachments of NbSi4 − The computational results presented in this study demonstrate a deviation from the findings of a previous Table 3 shows the electron detachment energies for the investigation concerning the neutral NbSi4 clusters. The anionic ground state 1 A′ of the A-NbSi4 − isomer, resulting previous study employed density functional theory with in the formation of neutral ground and excited electronic the B3LYP functional and the CCSD(T) method, which states. The detachment of one electron from the orbitals identified the 2 A1 state of a planar cyclic structure as the 33a′, 16a″, 32a′, 14a″, 31a′, 15a″, and 30a′ leads to the recommended neutral ground state.17 However, the results states 12 A′, 12 A″, 22 A′, 22 A″, 32 A′, 32 A″, and 42 A′, respec- obtained in this study demonstrate that the A-NbSi4 iso- tively. Based on the CASPT2 method, the corresponding mer, characterized by a trigonal bipyramidal structure with VDEs are estimated to be 2.42, 2.78, 2.94, 3.34, 3.86, 4.08, TA B L E 3 The ADEs and VDEs for the one-electron detachment processes of the anionic ground state 1 A′ of the A-NbSi4 − isomer. ADE (eV) VDE (eV) State Leading configuration Orbital CASPT2 expt. CASPT2 expt. A–NbSi4 – (Cs ) 1 A′ 30a′2 31a′2 32a′2 33a′2 14a″2 15a″2 16a″2 (80%) A–NbSi4 (Cs ) 12 A′ 30a′2 31a′2 32a′2 33a′1 14a″2 15a″2 16a″2 (74%) 33a′ 2.30 2.12 2.42 2.41 12 A″ 30a′2 31a′2 32a′2 33a′2 14a″2 15a″2 16a″1 (72%) 16a″ 2.78 2.92 22 A′ 30a′2 31a′2 32a′1 33a′2 14a″2 15a″2 16a″2 (73%) 32a′ 2.94 2.92 22 A″ 30a′2 31a′2 32a′2 33a′2 14a″1 15a″2 16a″2 (76%) 14a″ 3.34 3.29 32 A′ 30a′2 31a′1 32a′2 33a′2 14a″2 15a″2 16a″2 (58%) 31a′ 3.86 3.80 32 A″ 30a′2 31a′2 32a′2 33a′2 14a″2 15a″1 16a″2 (76%) 15a″ 4.08 4.18 42 A′ 30a′1 31a′2 32a′2 33a′2 14a″2 15a″2 16a″2 (62%) 30a′ 4.28 4.18
25728288, 2024, 2, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/vjch.202300355 by Readcube (Labtiva Inc.), Wiley Online Library on [01/05/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License TRAN 267 transition to 12 A′ in Figure 5 explain the broad shape of the first band at 2.41 eV. Overall, the CASPT2 results pro- vide interpretations for all five features in the photoelectron spectrum of NbSi4 − , whereas previous calculations using B3LYP and CCSD(T) could only explain the first band. 4 CONCLUSION Using DFT calculations with the BP86, PBE, B3LYP, and PBE0 functionals, as well as the CASSCF/CASPT2 method, this research provides valuable insights into the geometric and electronic structure of the NbSi4 −/0 cluster. The results uncover three significant isomers, with the most stable con- figuration being the bipyramidal isomer where the Nb atom is located in the equatorial position. The computed anionic and neutral ground states are identified as the 1 A′ and 2 A′ states, respectively. At the CASPT2 level, the ADE for the transition to the neutral ground state 12 A′ is estimated to be 2.30 eV. Also, the VDEs for the transitions from the F I G U R E 5 Vibrational progressions of the transition from 1 A′ to 2 A′ within the A-NbSi4 −/0 isomers obtained through multidimensional anionic ground state 1 A′ to the neutral states 12 A′, 12 A″, Franck–Condon factor simulation. 22 A′, 22 A″, 32 A′, 32 A″, and 42 A′ are estimated to be 2.42, 2.78, 2.94, 3.34, 3.86, 4.08, and 4.28 eV, respectively. In the Franck–Condon factor simulations, a significant vibrational and 4.28 eV. The ADE for the transition to the 12 A′ state progression is observed with frequencies of 98, 207, and is calculated to be 2.30 eV. Figure 5 displays multidimen- 286 cm−1 during the transition from the anionic ground sional Franck-Condon factor simulations for the transition state 1 A′ to the neutral 12 A′ state. By considering the ADE to the neutral ground state 12 A′, revealing significant vibra- and VDEs obtained from the CASPT2 calculations, along tional progressions originating from the totally symmetric with the results of the Franck–Condon factor simulation, normal modes with frequencies of 98, 207, and 286 cm−1 . all five features observed in the photoelectron spectrum These progressions are primarily due to substantial struc- of the NbSi4 − cluster are successfully explained. Overall, tural relaxations in the detachment of one electron from the study contributes to a comprehensive understanding the bonding orbital 33a′. These results provide valuable of the properties of NbSi4 −/0 clusters, encompassing their insights into the energy levels and electronic transitions geometric structure, electronic states, vibrational modes, during electron detachment from specific orbitals and are and photodissociation behavior. This expanded knowledge crucial in understanding the electron photodissociation enhances understanding of cluster chemistry and holds spectrum of the NbSi4 − cluster anion. potential implications for applications in materials science The photoelectron spectrum of NbSi4 − was measured and catalysis. using 266 nm photons. Five distinct bands were observed in the spectrum, with VDEs of 2.41, 2.92, 3.29, 3.80, and F U N D I N G I N F O R M AT I O N 4.18 eV. Also, the ADE of the first band was defined to be The author received no specific funding for this work. 2.12 eV. Because the electron selection rule in the photo- electron spectroscopy implies that only the one-electron CONFLIC T OF INTEREST detachment processes are allowed, all five features in the The author declares no conflict of interest. spectrum of NbSi4 − are interpreted based on the ADE and VDEs of one-electron detachment processes in Table 3. In D ATA AVA I L A B I L I T Y S TAT E M E N T particular, the first band with VDE of 2.41 eV corresponds to The data that support the findings of this study are available the transition from the anionic ground state 1 A′ to the neu- on request from the corresponding author. The data are not tral ground state 12 A′. The second band with VDE of 2.92 eV publicly available due to privacy or ethical restrictions. is explained by transitions to the 12 A″ and 22 A′ states. The third band with VDE of 3.29 eV is assigned to the transi- REFERENCES tion to the 22 A″ state, while the fourth band with VDE of 1. C. A. Marrache-Kikuchi, L. Berge, S. Collin, C. 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