Molecular Sources Of Ionospheric Holes

The dissociative recombination of molecular ions with electrons determines many of the properties of the Earth's ionosphere under both quiescent and disturbed conditions. However, in spite of its importance, there has never been an experimental measurement of dissociative recombination rates from individual excited ion vibrational levels. Completed are large scale ab initio calculations of cross sections and rates for the dissociative recombination of the molecular oxygen ion leading to excited oxygen atoms in the lS and ID states, the upper states of the well known green and red lines, respectively. A new method for calculating electronic autoionization widths using high Rydberg state wave functions to represent the inner part of the free electron wave function has been used and tested on the NO molecule where the widths can be calculated to an expected accuracy of about 15%. THe widths have been used to determine dissociative recombination cross sections as a function of electron energy. Large windows have been discovered in the cross sections from excited vibrational levels. The windows, at which the cross sections drop precipitously, are due to the overlap of the peak in the continuum vibrational wave functions.

Two multi-instrumented Terrier Malemute rockets including ion mass spectrometers were launched from Kwajalein on the nights of 17 and 23 July 1979 during equatorial Spread F events. Detailed ionospheric structure and composition measurements were made between about 100 and 590 km. The first flight penetrated six areas of 'bite-outs' spread over the range 265 to 560 km on upleg as well as several more depletions on downleg. The strongest irregularities, up to 90 percent depletion, occurred at the altitudes of 265 to 285 km just above the F region ledge at 250 km. There was no evidence of enhanced bottomside tracer ions (NO(+), O2(+) or meteoric ions) in any of the holes, which were composed mostly of O(+) and smaller amounts of N(+). From the composition signatures, the source of the bubbles appeared to be near the F region ledge. Within the higher altitude holes, the N(+)/O(+) ratios were smaller than the adjacent ionosphere ratios, indicating not only that the source regions were near the ledge, but also that the bubbles had initiated earlier when the ledge was at higher altitudes. While O(+) and N(+) exhibited strong fluctuations, NO(+) and O2(+) had fairly smooth profiles with scale heights similar to N2 and O2 respectively, demonstrating steady-state conditions and a stable neutral atmosphere with an exospheric temperature of about 1100K. This suggests that neutral atmospheric turbulence is not a major source of the ionospheric irregularities. Time periods for ion-chemical processes to achieve the observed composition are discussed in terms of bubble formation times and rise velocities.

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Unimolecular and Bimolecular Ion—Molecule Reaction Dynamics Cheuk-Yiu Ng, Ames Laboratory, Iowa State University, Iowa, USA Tomas Baer, University of North Carolina, NC, USA Ivan Powis, University of Nottingham, UK Recent advances in both experimental techniques and theoretical methodologies have meant that increasingly sophisticated studies concerning the formation, structures, energetics, and reaction dynamics of state- or energy-selected molecular ions can now be performed. In order to better serve the ion chemistry and physics community, each volume of this series will be dedicated to reviewing a specific topic, emphasizing new experimental and theoretical developments in the study of ions. This third volume is devoted to the study of unimolecular and bimolecular ionic processes. Special emphasis is given to studies related to planetary and interstellar ion chemistry and physics, the understanding of which has been a great impetus to the study of ion—molecule reactions. Each of the nine chapters making up this volume is written by a leading researcher in the respective field. This series will help stimulate new research directions and point to future opportunities in the fields of ion chemistry and physics.