RESONANT 2-PHOTON IONIZATION SPECTROSCOPY OF JET-COOLED AU3

A band system of jet-cooled Au3 has been located in the near infrared region of the spectrum using resonant two-photon ionization spectroscopy. The origin band is located at 13 354.15 cm-1 and the system extends more than 700 cm-1 further to the blue. The excited state displays a radiative lifetime of approximately 28-mu-s, corresponding to an absorption oscillator strength of f almost-equal-to 0.0003. Accordingly, it is thought that the transition corresponds to a spin-forbidden doublet (S = 1/2) to quartet (S = 3/2) transition, which is made allowed by spin-orbit contamination, presumably in the upper state. A progression in a totally symmetric stretching vibration (omega = 179.7 cm-1) is obvious in the spectrum, along with a much weaker progression in another mode, which displays an interesting pattern of splittings. Although no assignment is absolutely unambiguous, various candidates are presented. The most likely of these assigns the system as an A approximately 4E' <-- X approximately 2E' transition in the D3h point group, with both the ground X approximately 2E' and excited A approximately 4E' states undergoing Jahn-Teller distortion. The vibronic levels of the A approximately 4E' state have been fitted assuming a linear Jahn-Teller effect in a system with both spin-orbit splitting and a significant anharmonicity in the Jahn-Teller active e' vibrational mode. The combined effects of anharmonicity in the Jahn-Teller active mode and spin-orbit coupling appear not to have been previously investigated; they are therefore examined in some detail.