PHOTOELECTRON-SPECTROSCOPY AND ELECTRONIC-STRUCTURE OF CLUSTERS OF THE GROUP-V ELEMENTS .3. TETRAMERS - THE 2T2 AND 2A1 EXCITED-STATES OF P-4(+), AS-4(+), SB-4(+)

Methods employing high resolution HeI (584 Å) photoelectron spectroscopy have been applied to the tetrameric clusters of the group V elements, to resolve details of vibronic and spin-orbit structure in the first three electronic states of P4+, As4 +, and Sb4+. Measured spacings of distinct vibrational progressions in the ν1 mode for the 2A 1 states of P4+ and As4+, yield vibrational frequencies of 577 (5) cm-1 for P4 + and 350 (6) cm-1 for As4+. Franck-Condon factor calculations suggest bond length changes for the ions in the 2A1 states of 0.054 (3) Å for P4 + and 0.060 (3) Å for As4+. Strong Jahn-Teller distortions in the ν2 (e) Vibrational mode dominate the structure of the 2E ground states of the tetrameric ions. Both Jahn-Teller and spin-orbit effects appear in the spectra of the 2T2 states of the tetrameric ions, with the spin-orbit effect being dominant in Sb4+ and the Jahn-Teller effect dominant in P4+. Vibrational structure is resolved in the P4+ spectrum, and the ν3 (t2) mode is found to be the one principally active in the Jahn-Teller coupling. A classical metal-droplet model is found to fit well with trends in the IPs of the clusters as a function of size. © 1990 American Institute of Physics.