A general purpose projectile-frame expansion fitting method is used to characterize the shape of the electron capture to the continuum (ECC) cusp for bare carbon, oxygen, neon, and argon projectiles, incident on atomic and molecular hydrogen, and helium targets, over the velocity range 6–18 a.u. The method used to fit the ECC cusp shape allows the direct comparison of spectra taken under differing instrumental conditions in an apparatus-independent manner. The results reveal a substantial similarity in the ECC cusp shape for a wide variety of projectile Z, projectile velocity, and target combinations which has not yet been explained by current theories which predict the shape of the ECC cusp.

• Received 23 July 1984

DOI:https://doi.org/10.1103/PhysRevA.31.1392