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 D-3h structure and quenches Jahn-Teller distortion. They also predict a 0.2-eV spin-orbit splitting of the Au-3 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 a(1)(') and e(') stretching fundamentals and they confirm the D-3h geometry for Au-3. This work reports the first observation of the ground-state spin-orbit splitting of a heavy metal trimer.