He2-(4II sub g) Yields He2(X1 Sigma+) Autodetachment Energy Spectrum: Assessment of the He2 - and He2 Ground-State Potentials

摘要

The energy from the spin-forbidden electronic autodetachment from the metastable He2-4 Pig ion has been measured. The single-peaked continuum, resulting from a vertical transition to the repulsive will of the He2X 1sigma + ground state, has a maximum at 15.70 + or - 0.15 eV. For a rotationally cool beam, the spectrum is inconsistent with the existing potentials of He2- and He2X sigma +. A suitable fit, neglecting rotational effects, would require an increase of 0.06 A2 in the calculated Re of He2-. However a very good fit can also be obtained from the existing potentials by assuming a rotationally hot (15 000 K) distribution. Surprisingly, both fits require contributions from levels v > 0, which are known to undergo vibrational autodetachment to He2A 3 SIGMA U +. For such contributions, the latter process must be exceptionally slow (10 to the 6th power/s). Reprints. (AW)