Infrared vibronic absorption spectrum and spin–orbit calculations of the upper spin–orbit component of the Au3 ground state

Laser-ablated gold co-deposited with excess neon at 3.5 K produces a new sharp 2025.5-cm−1 absorption. Annealing to 8 K increases this absorption ten-fold and produces six weaker associated vibronic bands with 172- and 118-cm−1 intervals. Relativistic configurations (RCI) computations are carried out for several electronic states lying below 4.4 eV. These calculations show that the spin–orbit effect stabilizes the D3h structure and quenches Jahn–Teller distortion. They also predict a 0.2-eV spin–orbit splitting of the Au3 ground state, which is in excellent agreement with the 2025.5-cm−1 neon matrix band origin. We have also confirmed the assignment of the A-X system at 1.8 eV observed by Bishea and Morse. The observed vibronic intervals are in accord with calculated a1′ and e′ stretching fundamentals and they confirm the D3h geometry for Au3. This work reports the first observation of the ground-state spin–orbit splitting of a heavy metal trimer.