K X-ray production by 90-360 keV Ar and Ne collisions with Si. A comparison between gas and solid target experiments

K X-ray production in the collisions Ne + , Ne ++ to SiH 4 ; Si + , Si ++ to Ne and Ar ++ to SiH 4 has been studied in the energy range 90-360 keV. Ar(K) and Si(K) X-rays were looked for but not observed, and the production cross sections must be less than 10 -26 cm 2 , but Ne(K) X-rays were found and the corresponding cross section increases between 10 -24 and 3*10 -22 in the energy range studied, which agrees with expectations according to the electron promotion model of Fano and Lichten (1965). Comparison has been made of these ion-gas target results, with the previous ion-solid target results of Brandt and Laubert (1970) and Taulbjerf et al. (1973), and comment is made on the interpretation in terms of 'solid effects'. Within the framework of the Fano-Lichten model a rotational coupling of the 2p sigma MO to levels at or near the continuum is required to explain our observation of Ne(K) X-rays.