Partial destruction of beam-foil alignment by molecular projectiles

Abstract
The 3P1-3P2 659 MHz quantum beat pattern of the 388.9 nm 2s-3p HeI transition has been measured as a function of carbon foil thickness using both He+ and HeH+ projectiles with the He energies varying from 70 to 260 keV. It is shown that the beat amplitude ratio A(HeH+)/A(He+) is a strong function of the foil thickness. An appreciable destruction of the alignment results for molecular ions impinging on the thinnest foils, corresponding to the smallest distance of the molecular fragments. A qualitative explanation of the result is suggested.