Doppler shift of continuum x rays from heavy-ion collisions

The continuum $K$ x-ray spectrum from 200-MeV Kr + Zr has been found to undergo a Doppler shift with an effective Doppler velocity equal to $(0.92\mathrm{}\pm 0.03)v_{\mathrm{ci}}$, where $v_{\mathrm{ci}}$ is equal to the center-of-mass velocity of the intermediate Kr + Zr molecule, corresponding to the incident projectile velocity. If the x rays are indeed generated by quasimolecular processes, the expected Doppler velocity is $0.90v_{\mathrm{ci}}$, taking into account the slowing down of the projectile in the target. The anisotropy of the continuum spectrum in the c.m. system is derived.