Nonstatistical population of the 1s2p 21P1 and 23P1 states in recoil ions produced by heavy ion impact

It has been shown that the observed nonstatistical 1P/3P intensity ratio resulting from the radiative decay of He-like Ne 1s2p states produced in 80 MeV Ar ion collisions cannot be attributed to alignment. Contribution to the 1P population from 1s-2p excitation was found to be a possible cause of the discrepancy, however the magnitude of this contribution appears to be considerably higher than can be justified on theoretical grounds. In the hope of shedding more light on this problem, a series of measurements of the K x-ray spectra of O excited by Ar ion impact on O2, H2O and CO2 target gases was carried out. In an O2 molecule ionized by heavy ion impact, electron exchange can take place between the two O atoms in the early stages of the molecular explosion and this may affect the 1P/3P ratio due to the large difference in the lifetimes of the 1P and 3P transitions. In an H2O molecule, however, interatomic transfer effects should be absent. The K x-ray spectra of O in O2 and H2O gases at pressures of 15 and 10 torr are shown. Since the lifetime of the 23P1 state of He-like O is an order of magnitude longer than that of Ne, the 1P/3P ratio of O should show a much steeper pressure dependence than that of Ne. The measurements indicate, however, that the 1P/3P ratio is nearly constant as a function of pressure in the range from 10 torr to 50 torr. The extrapolated zero pressure limit of the 1P/3P ratio changes from 4.4 to 3.4 in going from O2 to H2O, and hence interatomic electron transfer as a reason for the nonstatistical ratio is again ruled out. Spectra of O2 and H2O were taken at several pressures with the reflection plane of the crystal oriented parallel and perpendicular to the beam direction, but no measurable effect of polarization on the 1P/3P ratio was found