Photoelectron spectroscopy and electronic structure of clusters of the group V elements. II. Tetramers: Strong Jahn–Teller coupling in the tetrahedral 2E ground states of P+4, As+4, and Sb+4

Abstract

High resolution HeI (584 Å) photoelectron spectra have been obtained for the tetrameric clusters of the group V elements: P₄, As₄, and Sb₄. The spectra establish that the ground ²E states of tetrahedral P⁺₄, As⁺₄, and Sb⁺₄ are unstable with respect to distortion in the ν₂(e) vibrational coordinate. The E⊗e Jahn–Teller problem has been treated in detail, yielding simulated spectra to compare with experimental ones. Vibronic calculations, extended to second order (quadratic coupling) for P⁺₄, account for vibrational structure which is partially resolved in its photoelectron spectrum. A Jahn–Teller stabilization energy of 0.65 eV is derived for P⁺₄, which can be characterized in its ground vibronic state as being highly distorted, and highly fluxional. Linear‐only Jahn–Teller coupling calculations performed for As⁺₄ and Sb⁺₄, show good qualitative agreement with experimental spectra, yielding stabilization energies of 0.84 and 1.4 eV, respectively.