We examine the implications of a traditional assumption of exospheric physics, that collisions of hydrogen atoms and protons preferentially result in charge exchange with negligible momentum transfer. Initially adopted as a necessary convenience to accommodate limited computer resources in exosphere model calculations, this approximation results in a direct transformation of the proton velocity distribution into a hot component of neutral hydrogen. It leads to significant enhancements in both escape and in the formation of extended planetary coronae. With expanding computational facilities, the need for the approximation has passed. As the first step toward its replacement with a realistic, quantum mechanical model of the H‐H+ collision process, we calculate differential and cumulative cross sections for quantum elastic scattering of indistinguishable nuclei for a fine grid of encounter energies and scattering angles. These data are used to study the nature of ionosphere‐exosphere coupling through H‐H+ collisions, and to demonstrate that the distribution of velocities of scattered H produced in the traditional exospheric charge exchange approximation, as well as that arising from an alternative, fluid dynamics approach, leads to unacceptable abundances of coronal atoms in long‐term, highly elliptic trajectories.

The microwave spectrum of methylphosphine has been investigated in the regions of 12–33 and 46–49 kMc. The rotational constants are found to be A = 71,869.5, B = 11,792.6, C = 11,677.7 Mc. Stark effect measurements yield a dipole moment of 1.100±0.010 D. The barrier to internal rotation of the methyl group, as determined from the A—E splittings of rotational lines in the ground torsional state and from the satellite frequency pattern of the 000—101 transition, is 685.2±5 cm—1. The structure of the molecule and the magnitude of the internal barrier in relation to other molecules are discussed.

The disagreement between model calculations of ionospheric N2+ concentrations and those measured by the Atmosphere Explorer (AE) satellite has been controversial for several years. The model calculations of N2+ require an additional loss of the order of ∼10² ions cm−3 s−1 at ∼250 km in order to account for the observed N2+ concentrations. After analysis of many orbits of AE data we have drawn the conclusion that such a loss rate could only be provided by either (1) enhancing the ionospheric dissociative recombination rate coefficient for N2+ by a factor of 2–3 over its currently accepted value if this is not precluded by laboratory data or (2) enhancing of the charge exchange of N2+ with atomic oxygen. This could be achieved by two mechanisms which either independently or combined can account for the observed N2+ concentrations. The first is the enhanced destruction of N2+ by charge exchange of vibrationally excited N2+ with O (enhancement of the branch to NO+ only transfers the problem to NO+). The second mechanism is the accidentally energetically resonant reaction O+(²D) + N2 ⇄ N2+(X)υ=5 + O. In spite of the valid theoretical arguments against the plausibility of these two mechanisms, without any viable alternatives we feel compelled to present our results. The best agreement between theory and data is obtained when these two mechanisms are combined with the rate coefficients for charge exchange of vibrationally excited N2+ with O increased by a factor of 50 and N2 set equal to 2.5×10−10 cm³ s−1 and where N2+(X)υ>0 is quenched by N2 at a rate of ∼5×10−10 cm³ s−1. An important aspect of the chemical scheme is negligible quenching of O+(²D) by O. We estimate an upper limit for the rate coefficient of this process to be ∼5×10−12 cm³ s−1.

We describe an investigation of the long‐term behavior of neutral hydrogen in the thermosphere as influenced by changes associated with the solar cycle. Hydrogen concentrations are derived from application of charge exchange equilibrium to ionospheric measurements in the low‐latitude F region with the AE‐C and AE‐E satellites. The adopted data base spans the years, 1974–1979, of increasing solar activity and daily average exospheric temperatures ranging between 700° and 1300°K. Statistical analyses yield the diurnal relative variations and mean concentrations of hydrogen at a reference height of 300 km. These mean concentrations generally agree with other measurements over smaller temperature intervals, with minor differences at the higher temperatures. The associated daily average evaporative escape flux tends toward a constant value above ∼1000°K; this behavior is consistent with theory for the total vertical flux, but the magnitude, near 108 cm−2 s−1, is smaller by a factor of ∼3 than values deduced by other means. The observed diurnal variation has an average near 2.5 at the low temperatures, decreasing to about 2 as the temperature increases, in agreement with some but generally larger than most reported measurements. Current theoretical models require the presence of neutral winds and/or diurnally varying charge exchange fluxes into and out of the plasmasphere to provide diurnal ratios as large as those reported here.

Measurements of O++ concentrations made by the Atmosphere Explorer C satellite are analyzed for altitudes where photochemical equilibrium conditions prevail in order to determine the photochemical sources and sinks of the doubly charged ion. The major loss process is found to be through partial charge exchange with neutral atomic oxygen with a rate coefficient of 1 × 10−11 cm³ s−1 with an uncertainty of 40%. Above 220 km the major source is photo‐ionization of O+. However, X ray ionization of O(λ ≤ 23.3 Å) producing O++ directly through the Auger process provides a better fit to the observed profile at lower altitudes. At solar maximum, particularly during solar disturbances, this process could be a major source of ionospheric O++ up to 500 km.