Ground‐based observations of atmospheric density profiles to 92 km were obtained for four successive seasons between summer 1989 and spring 1990. These results were obtained with a powerful Rayleigh lidar facility located at Wright Patterson Air Force Base (Dayton, Ohio). This instrument combined a 14‐W XeF laser transmitter with a 2.54‐m receiver mirror to observe returns from altitudes between 40 and 95 km. Analysis of the scale height dependence of the density profiles produced temperatures with a measurement error of about 5 K (∼2.5%) at 90 km when the lidar data was averaged for 20 min. and smoothed in height over 2.7 km. Examination of these profiles for the total of 18 nights showed that there often existed in the mesophere a layer of enhanced temperatures when compared with the U.S. standard profile. The layer centroid height was about 85 km for summer and 70 to 75 km for winter. Data obtained for the equinoctial periods showed the amplitude of these layers to be weak. The winter temperature profiles showed evidence forlong‐period waves passing through the region of the thermal anomaly while the equinox profiles revealed more sporadic wave activity with shorter vertical wavelengths. Both the winter and summer temperature data displayed regions where the observed lapse rate approached the adiabatic lapse rate. In the summer the wave activity near the inversion layer was weak.

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We report measurements of differential cross sections of rotationally (Δj = 15 to 79)–vibrationally (Δv = 1) inelastic collisions in ground electronic state Na2 with Ar on a level to level basis. The experiment is performed using crossed supersonic molecular beams and two dye lasers, one for tagging the initial level (v = 0, ji = 7), and the second for detection of the final level (v = 1, jf = 7+Δj) and scattering angle ϑ. A description of the experimental apparatus and technique is given. The differential cross sections all exhibit a pronounced rise at some minimum angle to a maximum followed by a gradual decline out to ϑ = π. The angular positions of the rise and peak increase nearly linearly with Δj. The Δv = 1, Δj integral cross sections are roughly constant in size even though the inelasticity (ΔE) varies over a large fraction of the available initial kinetic energy (∼2400 cm−1); by comparison, the Δv = 0, Δj integral cross sections, over a similar range in Δj, follow a power law dependence in ΔE. The qualitative features of both the differential and integral cross sections appear consistent within the framework of a classical, sudden collision on a sharply repulsive potential.

We have measured level to level differential cross sections for rotational level changing collisions in ground state Na2 with Ar: Na2 (v\=0, ji=7)+Ar→Na2 (v\=0, jf)+Ar. Measurements range in Δj(jf−ji) from −4 to 80 and in Θ to π. A seeded supersonic beam source produces rotationally cold Na2 with a narrow velocity distribution; the levels are isolated and the differential cross sections are measured with cw dye lasers, using a new technique, angular distributions using the Doppler shift. The differential cross sections display a sharp rise and slow decline, reaching a maximum at an angle which is roughly proportional to Δj. We term these features ’’halos’’. (AIP)

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