Jerry F. Bott

Shock‐Tube Studies of HF Vibrational Relaxation

The vibrational relaxation of HF has been studied behind incident shock waves in the temperature range 1350–4000°K by monitoring the 2.7−μ infrared emission. Relaxation times reduced to standard pressure were obtained for mixtures containing 1%–10% HF in argon and for mixtures containing N2, He, and D2. These data were used to calculate the relaxation times of HF due to these various gases. The relaxation times can be summarized by the expressions PτHF‐HF=1.02×10−2 exp(34.39/T1/3) μsec· atm, PτHF‐Ar=1.62×10−3 exp(111.97/T1/3) μsec· atm, PτHF‐He=1.52×10−4 exp(133.3/T1/2) μ sec· atm, and Pτ HF‐D2=5.1×10−4 exp(96.6/T1/3) μsec· atm. The values of PτHF‐N2 fell between those for helium and deuterium. The relaxation time of HF due to itself is compared to the predictions of several theories of V‐T and V‐R energy transfer, and to published experimental data for other hydrogen halides. The HF rates of this study, together with the measured rate at room temperature, suggest the possibility of an attractive potentia...

Temperature dependence of V‐V and V‐R, T energy transfer measurements in mixtures containing HF

A pulsed HF chemical laser has been used to excite HF molecules to their first vibrational level. The decay times of the infrared fluorescence from HF(ν = 1) have been used to determine the rate coefficients for energy transfer from HF to various collision partners including H2, D2, N2, O2, DF, HCl, CO2, NO, CO, and HBr. The experiments were performed at temperatures from 450 to 1000°K for most of the molecules. as well as at 295°K. For the higher temperature measurements, the experiments were performed behind a reflected shock wave in a shock tube. The compression heating capability of a shock tube has been used successfully as an alternative to a heated cell for laser‐induced fluorescence measurements. The room‐temperature probabilities of energy transfer from HF to the various molecules plotted versus energy mismatch fell along two distinct lines: one for homonuclear and one for heteronuclear molecules. The rate coefficients (cubic centimeters per mole second) for the molecules with the smallest energy...

HF Vibrational Relaxation Measurements Using the Combined Shock Tube‐Laser‐Induced Fluorescence Technique

Vibrational relaxation measurements in HF have been obtained at intermediate temperatures by combining the laser‐induced fluorescence technique with shock compression heating in a shock tube. Usually, shock tube measurements of vibrational relaxation are limited to high temperatures, above about 1300°K in the case of HF. Laser‐induced fluorescence measurements can be made in heated cells suitable for HF handling up to about 700–800°K. The combination of the two techniques offers several advantages including large range of temperatures, no wall reactions, and no leaky cells at high temperature. This method was used to obtain HF vibrational relaxation data at 460 to 1030°K and at 295°K. These data, together with shock tube data at high temperature (1350 to 3000°K), are compared with theoretical predictions. A measurement of the V‐V rate for the reaction HF (1) + HF (1) ⇌ HF (0) + HF(2) gave a value of 2.2 × 1013 cc/mole · sec.

Absolute rate coefficients for F+H2 and F+D2 at T=295–765 K.

The rate coefficients of the F+H2 and F+D2 reactions must be accurately known over a wide temperature range if the HF and DF chemical lasers are to be properly modeled. Although the pulsed and cw chemical lasers operate at elevated temperatures (500 to 2000 K), no absolute rate data exist for T≳400 K. Extension of the infrared multiphoton dissociation–infrared fluorescence technique permitted the following Arrhenius equations to be determined between 295 and 765 K: kF+H2=(1.3±0.25)×1014 exp[−(1182±100)/RT]; kF+D2=(6.4±2.2)×1013 exp [−(1200±142)/RT]; kF+H2/kF+D2=(2.1±0.8) exp[(18±250)/RT].

Shock‐Tube Studies of Sulfur Hexafluoride

Shock‐tube kinetic studies of SF6 dissociation in argon have been made in the temperature range of 1650°–2050°K at pressures from 0.13–30 atm. Rate constants for the initial fragmentation of SF6 have been determined and have been found to be explainable in terms of classical unimolecular reaction kinetics. The analysis of the data in terms of the RRK theory yielded S = 6, λD = 0.25, E0 = 75.92 kcal/mole, and A = 1012.95sec−1 as the best values of the unimolecular parameters. The data did not rule out values of 5 to 7 for S or a factor of 2 range in λD with corresponding variations of about 4 kcal/mole in E0 and a factor of 3 in A. E0 = 75.92 kcal/mole represents the strength of the first S–F bond. Both ir and uv techniques were used to obtain the data.

Vibrational relaxation of HF(v=1, 2, and 3) in H2, N2, and CO2

The vibrational relaxation times of HF(v=1, 2, and 3) were measured in H2, N2, and CO2 by a laser‐induced fluorescence technique. The upper vibrational levels were produced by sequential absorption in which HF(v=0) was pumped first to HF(v=1) and subsequently to HF(v=2) and HF(v=3) by photons from a pulsed multiline HF chemical laser. At T=295 K, the relaxation rates of HF(v=1), HF(v=2), and HF(v=3) in H2 were found to be, respectively, (1.43±0.15) ×10−2, (1.23±0.1) ×10−2, and (1.13±0.1) ×10−2 (μsec Torr)−1; in N2, (1.45±0.15) ×10−4, (8.1±1.0) ×10−4, and (2.92±0.3) ×10−3 (μsec Torr)−1; and in CO2, 0.039±0.004, 0.19±0.02, and 0.38±0.04 (μsec Torr)−1. Values of (7.5±1) ×10−4 and 0.4±0.04 (μsec Torr)−1 were obtained for the relaxation rates of HF(v=3) in O2 and HCl, respectively.

Gas‐dynamic corrections applied to laser‐induced fluorescence measurements of HF (v = 1) and DF (v = 1) deactivation

Partial‐pressure measurements in laser‐induced fluorescence measurements have been corrected for gas‐dynamic effects. These corrections bring a number of HF (v = 1) deactication measurements into close agreement.

Shock tube study of DF vibrational relaxation

The vibrational relaxation of DF behind incident shock waves in the temperature range 800–4000° K has been studied by monitoring the 3.5‐μm infrared emission. Relaxation times reduced to standard pressure were obtained for mixtures containing 1%–10% DF in Ar and for mixtures containing N2, H2, and F atoms. These data were used for calculation of the relaxation times of DF due to these various gases. The relaxation data can be summarized by P τDF–DF=1.4× 10−3exp (63.7/T1/3)  μsec·atm (above 2000°K), P τDF–Ar=7.1× 10−3exp (128.6/T1/3) μsec·atm, P τDF–H2=1.9× 10−2exp (35/T1/3) μsec·atm. The values of P τDF–N2 fell between those for Ar and D2. The deactivation rate of DF by F was measured to be 1.5× 1013cc/mole·sec. The measurements were compared to the predictions of several theories of vibration‐to‐translation and vibration‐to‐rotation energy transfer.

Temperature dependence of several vibrational relaxation processes in DF–CO2 mixtures

A pulsed DF chemical laser has been used to excite DF molecules to their first vibrational level. Decay of the infrared DF fluorescence was used to calculate the vibrational relaxation times of DF due to collisions with itself at temperatures between 468 and 920°K as well as at room temperature. The high temperature data were obtained in a laser‐induced fluorescence experiment performed behind a reflected shock wave in a shock tube. The relaxation time of DF(1) due to DF collisions was measured and determined to be 0.063± 0.005μsec · atm at 295°K increasing to 0.36± 0.03μsec· atm at 900°K, which was in agreement with previous shock tube measurements. A measurement of the rate for DF(1)+DF(1)⇄ DF(0)+DF(2) gave a value of kν ν=1.96± 0.2× 1013 cc/mole· sec at 295°K. The rate for the reaction DF(1)+CO2(000)⇄ DF(0)+CO2(001) rate was measured to be 115(μsec· atm−1 at 295°K decreasing to 32± 3(μ sec· atm)−1 at 720°K. Deactivation of CO2(001) by DF was measured to be 8.0± 0.8 (μ sec· atm)−1 at 470°K and 18± 2(μse...

Vibrational relaxation of DF (v=1–4) in D2, H2, N2, HF, and CO2

The deactivation of the upper vibrational levels of DF by H2, D2, N2, HF, and CO2 has been studied with the technique of laser‐induced fluorescence. The upper vibrational levels were produced by sequential photon absorption in which DF (v=0) was pumped first to DF (v=1) and subsequently to DF (v=2), DF (v=3), and DF (v=4) by photons from a pulsed multiline DF chemical laser. The deactivation rates (V−V+V−R,T) for all the collision partners except D2 scaled with vibrational level as vn with n=1.9 to 2.0 for v=1 to 4. Similar studies have indicated the somewhat larger value of n=2.7±0.2 for HF (v) deactivation by diatomic molecules.