M X-ray emission from low-energy, highly charged Taq+ (q = 45–49) ions colliding with neutral atoms due to singly and doubly excited states formed through single-electron capture

M X-rays have been observed from 1–40 keV/u 181Taq+ (q = 45–49) ions colliding with neutral Ar atoms under single collisions. The most dominant X-rays have been found to be due to transitions of 4p–3d and 4f–3d when the projectiles bring 3d-shell vacancies into collisions. Though much weaker, M X-rays also have been observed in collisions with Ta45+ ions that initially have no 3d-shell vacancy and are understood to originate from transitions of the doubly excited states 3d9nln'l' formed through strong electron–electron interactions after single-electron capture. The observed M X-ray spectra have been compared and reproduced nicely with the synthesized spectra. It has been confirmed that transitions of such doubly excited states also contribute to X-rays at the lower energy region observed even for higher charge ions with 3d vacancies. PACS Nos.: 32.30Rj, 32.70Cs, 32.80Rm, 34.70+e