Near‐Infrared Spectrum of the First Excited State of Au₂.

Förstel, Marko; Pollow, Kai; Studemund, Taarna; Dopfer, Otto

Au2 is a simple but crucial model system for understanding the diverse catalytic activity of gold. While the Au2 ground state (X2Σg ) is understood reasonably well from mass spectrometry and computations, no spectroscopic information is available for its first excited state (A2Σu ). Herein, we present the vibrationally resolved electronic spectrum of this state for cold Ar‐tagged Au2 cations. This exceptionally low‐lying and well isolated A2Σ(u) ←X2Σ(g) transition occurs in the near‐infrared range. The observed band origin (5738 cm−1, 1742.9 nm, 0.711 eV) and harmonic Au−Au and Au−Ar stretch frequencies (201 and 133 cm−1) agree surprisingly well with those predicted by standard time‐dependent density functional theory calculations. The linearly bonded Ar tag has little impact on either the geometric or electronic structure of Au2 , because the Au2 ⋅⋅⋅Ar bond (∼0.4 eV) is much weaker than the Au−Au bond (∼2 eV). As a result of 6 s←5d excitation of an electron from the antibonding σu* orbital (HOMO‐1) into the bonding σg orbital (SOMO), the Au−Au bond contracts substantially (by 0.1 Å).

EXCITED states; TIME-dependent density functional theory; ELECTRONIC excitation

Chemistry - A European Journal, 2021, Vol 27, Issue 61, p15074

0947-6539

Academic Journal

10.1002/chem.202102542