The autoionisation of doubly excited atomic states with one electron excited much more than the other is considered in the one-configuration approximation. The theory is asymptotic in the large angular momentum of the highly excited electron. The direct process results in the ejection of the high Rydberg electron whereas in exchange autoionisation the inner excited electron is ejected and the outer electron passes into the low-lying orbital. The multipole expansion of the interaction reduces the calculation of the direct autoionisation to finding the asymptotic behaviour of the one-electron matrix element between highly excited and continuum states for some power of the radial variable. Slater-type or Coulomb wavefunctions are used for the Rydberg electron and plane waves or Coulomb waves are employed for the ejected electron. The asymptotic behaviour of the two-electron matrix element is found for the exchange autoionisation and also for the exchange-type correction to direct autoionisation.
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