K-vacancy, molecular-orbital X-ray, and positron production in heavy-ion collisions

Recently proposed mechanisms of vacancy creation in 2p sigma and 1s sigma molecular orbitals by electronic transitions to high-lying vacant sites, and to continuum states are described. The filling of a 1s sigma vacancy during the collision by electronic transitions from higher-lying filled MO's gives rise to MO K x rays. For energetic collisions of very heavy ions, a 1s sigma vacancy might be filled by an electron from the negative energy Dirac sea, thereby creating a positron. Open questions are discussed. 36 references. (author)