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

Abstract

We measured the photoelectron spectra of diatomic AuSi and AuGe and conducted calculations on the structures and electronic properties of AuSi and AuGe. 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 Σ anionic ground state to the Π (Π and Π), Σ, 3Σ, and 4Σ 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 (Π-Π) of AuSi and AuGe measured in this work are in agreement with the literature values. The energy difference between the Σ (A) and Π 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 3Σ (B) and 4Σ (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.

AuSi molecule revisited: IOTC/CASSCF/CASPT2 calculations

“…The results presented in Table 6 confirm the good performance of the relativistic IOTC method. Our spectroscopic constants for X 2 Π 1/2 and 1 2 Π 3/2 states exhibit similar patterns when compared with the DK results of Abe et al [ 25 ] and of Tran et al [ 29 ] We have to stress that there are differences in the computational setup used in previous studies—Abe et al [ 25 ] used their own basis sets: Au[8s7p6d4f2g] and Si[5s4p2d], while Tran et al [ 29 ] used the ANO‐RCC‐VTZP one. The former seems to be unbalanced for Si (compared to Au).…”

“…The most recent paper on AuSi/AuSi − of Tran et al [ 29 ] represents the combination of experimental and computational studies using the DKH2 Hamiltonian. They reported the photoelectron spectra, bond distances, and harmonic frequencies of the ground and low‐lying excited states.…”

“…The basis sets used in the Abe et al study [ 25 ] were optimized within the DK3 Nakajima Hamiltonian, and the contractions were as follows: [29s26p15d12f6g/8s7p6d4f2g] for Au and [17s12p5d/5s4p2d]. In the work of Tran et al, [ 29 ] the triple‐ ζ atomic natural orbital‐relativistically contracted (ANO‐RCC) sets were used, with contraction schemes of [24s21p15d11f4g2h/8s6p5d3f2g] for Au and [17s12p5d4f2g/5s4p2d1f] for Si . In both calculations, due to convergence problems, it was impossible to obtain full potential energy curves for the states considered, and the authors managed to scan only a part of the curves around a minimum.…”

Relativistic calculations of AuSi+ and AuSi−

“…Our pilot spin‐free calculations for AuSi ions were made some time ago using the second‐order Douglas‐Kroll‐Hess (DKH) method. There is only one paper on AuSi − ion published by Tran et al, it represents the combination of experimental and computational study of the AuSi / AuSi − and AuGe / AuGe − pairs. They reported the photoelectron spectra, bond distances, harmonic frequencies of the ground state and two low lying excited states.…”

“…Theoretical and experimental studies of the electronic structure and spectra of the AuSi gold silicide molecule attracted the attention of experimentalists and theoreticians in the past . Little is known about the related structures of AuSi + cation and AuSi − anion.…”