Deuterium ions D+and doubly-charged helium ions He++have the same mass-to- charge ratio (M/Z= 2) and are not distinguished by the mass-spectrometer. On the basis of analysis of published data, Interkosmos-24satellite data, and theoretical estimations, it is shown that in the ionosphere and plasmasphere the ion with a mass number of two is He++and not D+, at least at altitudes of higher than 600–800 km. Arguments in favor of the validity of this assumption at lower altitudes are presented. Regularities of the dependence of the N(He++)/N(He+) ratio on altitude, time of day, season, and solar activity are derived. It is found that in the daytime the N(He++)/N(He+) ratio decreases with increasing solar activity. The seasonal dependence is most pronounced at nighttime in the altitude interval 1000–2000 km, where this ratio decreases in passing from winter to summer. Peculiarities of the latitude distribution of the absolute and relative values of the He++concentration are found in the Interkosmos-24satellite data. On the basis of the same data, a strong longitude effect in the N(He++) concentration occurring under certain heliogeophysical conditions is discovered, an effect amplitude attaining one order of magnitude on adjacent orbits. An interpretation of this effect is given.

The altitude and latitude behavior of the oxygen O-18(+) isotope and the ratios of ion densities (O-18(+)/O-16(+)) at altitudes of 500-1800 km, as well as the dependence of this ratio on geophysical conditions, were investigated by data obtained aboard the Interkosmos-24 satellite. This ratio is found to increase at high latitudes with a maximum observed near the auroral oval region. Sometimes, the maximum in latitude distribution of this ratio is observed at middle latitudes. During the effects of the equatorial anomaly at low latitudes, the ratio of the ion densities of oxygen isotopes decreases in the region of "humps" of the equatorial anomaly in comparison with the middle latitudes. An altitude dependence of the ratio of ion densities of oxygen isotopes is obtained for the middle latitudes; these data and the data published previously cover altitudes from 200 to 1800 km. Values of the ratio vary from 1.5 x 10(-3) to 0.35 x 10(-3) for different altitudes with scattering up to approximate to 30%. The altitude dependence of the ratio obtained for high latitudes differs from the dependence for middle latitudes by higher values and their larger scattering. During periods of high geomagnetic activity, the ratio of ion densities of oxygen isotopes is higher than under quiet conditions. It is suggested that the value of the ratio of ion densities of oxygen isotopes is determined by ion and neutral temperatures alike, and also by dynamical processes leading to ion lifting from lower altitudes.