First spectroscopic observation of gold(I) butadiynylide: Photodetachment velocity map imaging of the AuC4H anion

The velocity map imaging technique was used in the investigation of gold(i) butadiynylide, AuC₄H⁻, with images recorded at two excitation wavelengths. The resultant photodetachment spectra show a well defined vibrational progression in the neutral with an energy spacing of 343 ± 3 cm⁻¹. The adiabatic electron affinity was determined to be 1.775 ± 0.005 eV and assigned to the X¹Σ⁺←X²Σ⁺ transition between the anionic and neutral ground states. Franck-Condon simulations performed on density functional theory optimized geometries assisted the assignment of linear geometries to the neutral and anion and the observed vibrational progression to that of the Au-C₄H stretch.