Titanium Digermanium: Theoretical Assignment of Electronic Transitions Underlying Its Anion Photoelectron Spectrum

Abstract

Electronic structures of both the anionic and neutral triatomic species TiGe were theoretically studied employing single-reference (DFT and RCCSD(T)) and multiconfigurational (CASSCF/CASPT2 and CASSCF/NEVPT2) methods with large basis sets. The ground state of TiGe (C) was identified to be B, but the A state is nearly degenerate, whereas the B is clearly the ground state of the neutral TiGe (C). On the basis of the computed ground and excited states of both neutral and anionic structures, all electronic transitions giving rise to experimental anion photoelectron bands in the spectrum of TiGe can now be assigned. The X band of the anion photoelectron spectrum is attributed to a one-electron transition between two ground states B → B. Three neutral excited states 2A, 2B, and 3B are energetically responsible for the B band upon one-electron photodetachement from the anionic ground state B. The C band is assigned to the transition B → 2A. A transition from the nearly degenerate ground state A of the anion to the low-spin A of the final neutral state can be ascribed to the A band. Furthermore, the first two bands' progressions, whose normal vibrational modes were accessible from CASSCF/CASPT2 calculations, were also simulated by determination of multidimensional Franck-Condon factors.

Energetic degeneracy and electronic structures of germanium trimers doped with titanium

“…Based on the experimental spectroscopic data and quantum computations, multireference features were proven to be the main features of TiGe -/0 2 , and nearly degenerate electronic states are the origin of all electronic transitions causing visible bands in the experimental spectrum of TiGe -2 . 23 A larger size of germanium doped with titanium (TiGe -/0 3 ) was spectroscopically reported as well. 19 The anion photoelectron spectrum of TiGe -3 is more complicated than that of TiGe -2 with regard to the number of visible bands, 19 which means that more electronic transitions were observed in the experiment.…”

“…Hence, simultaneous utilization of both single reference and multireference methods to support and confirm results of each other are expected to be more reliable in description of non-single reference systems. 23,24,[30][31][32] As mentioned above, germanium clusters doped with transition metals are expected to be multiconfigurational and energetically degenerate. Based on the experimental spectroscopic data and quantum computations, multireference features were proven to be the main features of TiGe -/0 2 , and nearly degenerate electronic states are the origin of all electronic transitions causing visible bands in the experimental spectrum of TiGe -2 .…”

“…20 For pure germanium clusters and their metal doped ones, energetic degeneracy and multiconfigurational features were found to significantly contribute to the potential energy surfaces of corresponding clusters. [21][22][23][24] As a result, single reference methods (DFT, CCSD(T)) may not give reliable energetic values. [25][26][27][28][29] To accurately describe such systems and their excited states, the use of multireference quantum chemical methods is inevitable.…”

A density matrix renormalization group investigation on the electronic states of MnGen−/0/+ (n = 1–3) clusters

“…The mass‐selected anion photoelectron spectroscopy and density functional theory (DFT) were applied to explore the structures and properties of a large number of transition metal‐doped germanium clusters [1–24]. The electronic states of small transition metal‐doped germanium clusters were explored with the multiconfigurational CASSCF/CASPT2 and RASSCF/RASPT2 [25–30]. From these experimental and theoretical studies, a large number of stable endohedral structures in which the transition metal atom is encapsulated inside a germanium cage were proposed [1, 2, 5, 7, 8, 10, 14, 24, 31].…”

Exploring the structural stability order and electronic properties of transition metal M@Ge12 (M = Co, Pd, Tc, and Zr) doped germanium cage clusters

“…Electronic and structural properties of transition metal encapsulated in germanium clusters are incredibly dynamic area of exploration because of its significant in building block for clusters assembled materials and other expected applications in numerous fields [1][2][3][4][5][6][7][8][9][10] . Without a doubt, doping in silicon confine clusters has additionally stood out because of its applications in nanoelectronic gadgets and building blocks nanomaterials [7][8][9][10] . The decision of various sort of transition metal molecules prompts the much attractive legitimacy in the properties of these confine clusters.…”