Atmospheric absorption of 10.6-mu radiation can either heat or cool the air, depending upon atmospheric conditions. Absorption by CO(2) is essentially from the (100) to the (001) states. The depleted (100) state is rapidly replenished by energy transfer from translation, cooling the atmosphere. The (001) state slowly transfers energy through the N(2) back to translation, eventually heating the atmosphere. Cooling increases the density and index of refraction, and the resulting gradient tends to focus a gaussian beam. This partially offsets the usual heating effects and associated ray divergence.

Selective OD bond dissociation of HOD: Photodissociation of vibrationally excited HOD in the 5 O D statePhotoacoustic measurements of the vibrational relaxation of the selectively excited ozone ( 3 ) molecule in pure ozone and its binary mixtures with O 2 ,N 2 , and noble gasesThe rate constants associated with the deactivation of vibrationally excited CO 2 *(P3) by collision with either CO2 or N2 have been experimentally determined from 300 o -1000oK by a laser fluorescence method. The reactions investigated were k.where the asterisk denotes a vibrationally excited molecule, and the quantities in parentheses represent the specific excited modes of CO2. The rate constant k6 varies with temperature T (OK) as 8.60X10 7 jP/2 torr-I. sec-I. From 4OO o -1000oK the rate constant kl (per torr-I 'second-I ) varies with temperature aswith A = 6.79 and B = 30.8. From 300°-4QOoK the measured values of kl are greater than those corresponding to the above relation. The rate constant k6 increases from a value of 110 torr-I'sec l at room temperature to a value of 2700 torr-I. sec-1 at 1000oK, but the variation of k& with temperature cannot be simply expressed. The rate constant kl was found to be negligibly small compared to the other rate constants.

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IntroductionThe measurement of the total radiant intensity of air at superorbital entry conditions (e.g., T= 15 000°K, p/po=3XlO-1) requires a detector with a fast-response time and wide spectral coverage including both the Fast-llesponse Total infrared (IR) and the vacuum ultraviolet (VUV). These requirements are best met with a total thermal radiation Thler al ]Ra diation detector and we shall discuss our experience with both thin-film heat-transfer gauges and pyroelectric detectors. IDetectorsThe VUV region must be included in a total intensity measurement because over half of the total intensity can occur at wavelengths< 1200 A. Thus, there can be no ALLEN D. WOOD window between the hot gas and the detector surface. J. C. ANDREWS, Member, IEEE This condition has led us to the gauge-in-cavity model Lockheed Missiles and Space Company shown in Fig. 1. This model was located in the end of a Palo Alto, Calif.12-in-diameter, arc-driven shock tube and all testing was done in the reflected shock region. The essential feature of the gauge-in-cavity model is that the thermal detectors are located in a cavity and are Abstract irradiated through a small windowless aperture. The testing time is dictated by the time taken for the starting The construction, calibration, and performance of tin-film heatshock in the cavity to reach the detector-for a spacing transfer gauges in a measurement of the total radiant intensity of air of 5.6 cm this was about 15 ,s. Any effect of emission at superorbital entry conditions are discussed. It is shown that reliand absorption in the gas flow behind the starting shock ance on an electrical bridge calibration alone can cause erroneous was negligible because of the large expansion ratio into results. Magnetic interference from the shock tube flow was identi-the cavity. The optical stop permitted measurements to be fied and eliminated by model design and shielding. Thin-film gauges made at various gas path lengths between 1 and 12 cm are shown to be fundamentally unsuited for total radiation measure-which enabled the effects of self-absorption to be studied.ments because of noise caused by vacuum ultraviolet irradiation. The model contained eight thermal detectors (four per Pyroelectric thermal detectors avoid this difficulty and offer several side) located radially about the apertures. Provisions other advantages over thin-Mm gauges. The basic equations and prac-were made for a window to be placed at the aperture tical considerations in the use of pyroelectric gauges are discussed.which served as a spectral filter to eliminate the VUV. A quartz (Suprasil) window transmitting above about 1600 A was very convenient for this purpose. With these features of the measurement problem in mind, certain basic considerations of the construction and calibration of thin-film heat-transfer gauges will be presented and followed by an account of the difficulties ,flash tubes, pyroelectric, encountered during the course of the experiment. Finally,

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