Experimental measurements of the O2 dissociation rate in shock-heated oxygen-argon mixtures were obtained with the ultraviolet light absorption technique described in the preceding article. The dissociation rate constant kAr for the reaction O2+Ar→O+O+Ar can be fit over the temperature range from 3400 °K to 7500 °K by the theoretical formula kAr = C(D/RT)n−12 exp(−D/RT), where C = 6.0×101±20% cc/mole-sec and n = 1.5±0.2. 0 = 5.116 ev is the oxygen dissociation energy; R is the gas constant; and T is the temperature. This result is compared with the classical collision theory and the theories of Wigner and Keck. The rates for the dissociation of O2 by O and O2 were also determined; compared to the argon rate constant kO≈25kAr, kO2⪅3kAr Our experimental results are compared with those of Byron and Matthews. The relaxation times for dissociation and vibration are observed to be comparable at about 8000 °K. The experimental data indicate that the dissociation rate above 8000 °K is at least a factor of two less than the expected rate when the vibration is not in equilibrium (the vibrational temperature being less than the translational temperature) during dissociation.
This paper and the one following [M. Camac and A. Vaughan, J. Chem. Phys. 34, 459 (1961)] discuss the use of a new experi-mental technique for the determination of O2 vibration and dissociation rates. The concentration of O2 in the ground vibrational state can be inferred from measurements of ultraviolet light transmission at 1470 A. O2 has a strong continuous absorption band in this vacuum ultraviolet region. The vibrational relaxation rate of O2 in shock-heated O2-Ar mixtures was obtained from 1200 °K to 7000 °K. For Ar-O2 collisions, the measured relaxation time t, can be fit by the Landau-Teller theory [L. Landau and E. Teller, Physik. Z. Sowjetunion 10, 34 (1936)] 1/τv = nC1T1/6[1−exp(−2228T)]exp(−(C/T)1/3), where n is the number of particles/cc and T is the temperature in °K. C1 = 1.2×10−7 cc/particle∼sec-(K)1/6 and C = 1.04×107 (±30%)°K. The observed vibrational relaxation time for O2-O2 collisions is 5.0±0.5 times faster than that for O2-Ar collisions. The experimental results are compared to the theoretical predictions of Schwartz and Herzfeld [R. N. Schwartz, Z. I. Slawsky, and K. F. Herzfeld, J. Chem. Phys. 20, 1591 (1952); R. N. Schwartz and K. F. Herzfeld, ibid. 22, 767 (1954)]. At the lower temperatures, the O2-O2 rates given by Blackman [V. H. Blackman, J. Fluid Mech. 1, 61 (1956)] have a different temperature dependence than the O2-Ar rates obtained in this experiment.
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.
The energy that an ion must expend in a silver halide grain in order to render it developable is very small compared to the original energy of the ions used in this investigation. Hence, the lack of 100% detection efficiency is probably caused by the extremely small penetration of the ion into the emulsion. If this is the case, the efficiency measured represents the fraction of the ions which enter the emulsion at a point where their range in the gelatin is greater than the distance to the first grain THE REVIEW OF SCIENTIFIC INSTRUMENTS in their projected path. The estimated ranges of the ions in gelatin are listed in Table I. These values are based on some measurements of the energy losses of ions in traversing thin organic films done at this Laboratory.The correlation between range and efficiency is shown in Fig. 1. This shows that the probability of reaching a grain becomes! for a range of 0.5 J.L. This appears reasonable for this emulsion which has an average grain size of about 0.2-0.4 A new type of heat transfer gauge that operates in the presence of highly ionized plasmas and in strong electric and magnetic fields has been developed. The principle of its operation is to use a thin opaque surface as the heat transfer element. Aerodynamic and radiative heating is applied to one side of this layer, while measurements are made of the change of the infrared emission from the other side. This system is essentially a bolometer. Since the gauge is initially at room temperature, the predominant radiation from the opaque layer is in the infrared band from 5 to 30 p.. Changes in the temperature of the element are determined by the variation in its infrared emission. The opaque layer is made thin enough so that the temperature of the front surface can be determined in less than 0.1 p.sec. This paper describes the components of the heat transfer system and the methods for calibrating the gauge for heating pulses of long and short duration. Gauge calibrations by heat pulses from shock heated air are presented, and the response time of the gauge to short heat pulses is evaluated.
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