Classical trajectory calculations have been performed to determine the reaction rate constants and NO final vibrational‐rotational distributions of the N(4S) + O2 reaction at hyperthermal translational energies. The reaction occurs on two electronic potential energy surfaces, both of which must be considered for a realistic description of the N(4S) + O2 dynamics. The calculations, which are in good agreement with the available experimental data, show that the reaction has a very strong translational energy dependence and produces NO with extensive vibrational and rotational excitation. The present study provides the N(4S) + O2 reaction attributes necessary to predict NO formation and emission from translationally hot N(4S) in the thermosphere.
A new optical hydrogen sensor based on spontaneous Raman scattering of laser light has been designed and constructed for rugged field use. It provides good sensitivity (better than 100 parts in 10(6)), rapid response (several seconds), and the inherent Raman characteristics of linearity and background gas independence of the signal. Efficient light collection and discrimination by using fast optics and a bandpass interference filter compensate for the inefficiency of the Raman-scattering process. A multipass optical cavity with a Herriott-type configuration provides intense illumination from an air-cooled cw gas laser. The observed performance is in good agreement with the theoretical signal and noise level predictions.
A 2‐kW electron accelerator was launched in October 1974 from the White Sands Missile Range, New Mexico, as the initial launch in the Excede series of artificial auroral experiments. The launch, designated Precede, was supported by a number of ground‐based optical systems to record the electron‐induced atmospheric emissions as a remote diagnostic technique of accelerator performance in addition to recording emissions of aeronomic interest in a controlled artificial aurora. The electron source, square wave modulated at 0.5 Hz, was initiated at 95 km on payload ascent and continued through apogee (120 km) to a descent altitude of approximately 80 km, providing a total of 90 pulses of the 2.5‐kV 0.8‐A electron beam over a period of 180 s. A rocket‐borne retarding potential analyzer provided a measure of the energy distribution of electrons returning to the vehicle skin. The energy distribution of the return current electrons has been compared with laboratory measurements of the energy distribution of secondary electrons as a function of scattering angle to infer a vehicle potential due to a net positive charge buildup on the electron‐emitting payload. The steady state vehicle potential at apogee is less than 30 V, with substantially smaller values determined at lower altitudes. Langmuir probe theory is shown to model accurately the altitude dependent steady state vehicle potential. Ground‐based optical systems included an image‐intensified spectrograph and a dual channel telephotometer recording the time dependent emission profile of the N2+ (B²Σu+ → X²Σg+) first negative (0‐0) band at 3914 Å and the O(¹S → ¹D) transition at 5577 Å. The spectrograph recorded emissions in the 4200‐ to 8500‐Å wavelength range including the prominent transitions of the N2+ first negative, N2(B³Πg → A³Σu+) first positive and N2+ (A²Πu → X²Σg+) Meinel systems as well as the O(¹S) 5577‐Å line. With the exception of the N2+ first negative system the image‐intensified spectrograph indicated that these emissions are collisionally deactivated in the 80‐ to 110‐km altitude range. The ground‐based telephotometer measurements were corrected for the effects of atmospheric extinction by monitoring the apparent photon emission rates of several bright stars. An electron‐induced luminous efficiency of (4.5 ± 0.4) × 10−3 was determined for the N2+ 1 N (0‐0) transition at 3914 Å in the 80‐ to 100‐km altitude range.
This paper describes a laser interferometer which provides absolute distance measurements using tunable lasers. An active feedback loop system, in which the laser frequency is locked to the optical path length difference of the interferometer, is used to tune the laser wavelengths. If the two wavelengths are very close, electronic frequency counters can be used to measure the beat frequency between the two laser frequencies and thus to determine the optical path difference between the two legs of the interferometer.
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