Kurt L. Wray

Shock‐Tube Study of the Kinetics of Nitric Oxide at High Temperatures

A shock‐tube program was carried out in which the NO concentration was followed as a function of time behind the shock front by absorption of 1270 A radiation, where ground vibrational state O2 and N2 are essentially transparent. The absorption coefficients of the species NO, O2, and N2 as functions of the respective vibrational temperatures were determined by measuring the absorption by the shock‐heated gas at a point in the time history corresponding to complete vibrational relaxation but before the onset of dissociation.Time history analyses were made on a total of 42 shock‐tube runs covering a temperature range of 3000°—8000°K on the following six mixtures: ½% NO, ½% NO+¼% O2, 10% NO, 50% NO, 20% air, and 100% air—the diluent in all cases being argon.An IBM 704 computer was programmed to integrate the vibrational and chemical rate equations as a function of time behind the shock front, subject to the constraints of the conservation equations. The pertinent rate constants were varied in a systematic tr...

Shock‐Tube Study of the Coupling of the O2–Ar Rates of Dissociation and Vibrational Relaxation

At low temperatures the vibrational relaxation time τv is much shorter than the dissociation time τd. The O2–Ar results of Camac [J. Chem. Phys. 34, 448 (1961)] and Camac and Vaughan [J. Chem. Phys. 34, 460 (1961)] yield τd/τv=60 at 5000°K and, upon extrapolation, τd/τv=1.4 at 18 000°. According to these extrapolations, dissociation at high temperatures would proceed significantly before vibrational equilibration would occur. The purpose of this investigation was to determine how the dissociation rate will be affected by a lack of vibrational equilibrium. Studies of the dissociation rate of dilute O2–Ar mixtures were made in a 24‐in. diam shock tube from 5000°—18 000°K. The O2 concentration was monitored by its absorption of 1470 A radiation. An Arrhenius plot of the data yielded a straight line from 5000°—11 000°K, the rate constant being given by kd=2.9(±12%)×1014 exp (—D/RT)cc/mole‐sec. Above 11 000° the data deviate from the line given by this equation—at 18 000° kd being 0.45 times the calculated val...

Shock‐Tube Study of the Vibrational Relaxation of Nitric Oxide

The vibrational relaxation time of nitric oxide in NO–Ar mixtures was determined over the temperature range 1500°—7000°K. An ultraviolet absorption technique using 1270‐A radiation was employed to monitor the vibrational temperature as a function of time after these mixtures were shock heated to high translational temperatures. P10, the transition probability per oscillator per collision for transition between vibrational levels 1 and 0 calculated from the measured relaxation times ranged from 1.0×10—3 at 1500°K to 2.8×10—2 at 7000°K for NO–NO collisions. Argon is about 1/50 as efficient as NO. The results are compared with the lower temperature (400°—1500°K) work of Robben and with the adiabatic theory of Schwartz, Slawsky, and Herzfeld and the nonadiabatic theory of Nikitin.

Excitation Studies on the N2(1+) and N2+(1—) Systems in Shock‐Heated N–N2 Mixtures

The rate of excitation of the N2(1+) and N2+(1—) band systems was observed in shock‐heated N–N2 mixtures in which the initial mixture ratio N/N2 ranged from 0 to 0.27. A pulsed discharge prior to diaphragm rupture produced the N atoms; their concentration was determined by monitoring the decay of the Lewis—Rayleigh afterglow for about 50 msec subsequent to the discharge and up to the arrival of the shock. The shock waves produced temperatures in the range 7000°—18 600°K close to the shock front, after rotational relaxation. The radiation intensities from the N2(1+) (6600 to 8000 A) and N2+(1—) (0, 1) (4272 A) bands were monitored as functions of time behind the shock front. The initial slopes of the radiation‐time histories were compared with theoretical slopes. The rate‐constant expression for exciting ground‐state nitrogen X 1Σg+ to the A 3Σu+ state by collisions with N atoms was found to be kN = 1.9×10−6T−32 exp(—EXA/kT) cm3/particle·sec, where EXA = 6.168 eV. This yields an effective cross section of ...

Shock Tube Study of the Effect of Vibrational Energy of N2 on the Kinetics of the O+N2→NO+N Reaction

The kinetics of the reaction O+N2+3.3 eV→NO+N were investigated under conditions where the vibrational temperature of the nitrogen was less than the translational temperature. The formation of NO behind incident shock waves in dilute O3–N2 mixtures was studied over the temperature range 3100–6400°K with initial pressures of 2–25 torr. In the shock front O3→O+O2 and the reaction of the O with N2 is then rate‐limiting, followed by the fast reaction N+O2→NO+O. The NO was monitored in emission at 5.3 μ and the initial slopes were compared to theoretical calculations which included vibrational relaxation processes. The radiation rose linearly from the shock front with no incubation in accord with the theoretical calculations employing only translational energy to determine the fraction of collisions whose energy was above the endothermicity of reaction.

Vibrational Relaxation of CO by Fe-Atoms.

Abstract : Shock tube investigations on Fe(CO)5 + Ar mixtures are described. Behind incident shocks we observe immediate decomposition of the iron pentacarbonyl to yield Fe and vibrationally cold CO; the CO is then very efficiently relaxed by the Fe-atoms. The results are interpreted to yield a relaxation time for CO infinitely dilute in Fe at 1 atm of P(tau)(CO, Fe) of about 0.06 atm micro sec for T = 1400-2900K. This is believed to be the first measurement of vibrational relaxation by metal atoms. (Author)

Shock Tube Study of the Decomposition Kinetics of SO2F2

Recent thermal decomposition studies of SF6 have led to interest in its principal oxidation product, sulfuryl difluoride. In the present study the thermal stability of SO2F2 at high temperatures has been investigated. Highly dilute SO2F2–Ar mixtures (∼ 0.1%) were shock heated in a conventional 1.5″ stainless‐steel shock tube. The SO2F2 concentration was monitored as a function of time behind the incident shock wave by its infrared emission at 11.7 μ utilizing a liquid helium cooled Cu:Ge detector. The initial pressure in the shock tube was varied from 30 to 600 torr and the temperature range covered was 1900–2300°K. The monitored radiation was shown to be transparent over the range of densities employed. Effective first‐order rate constants were evaluated from the logarithmic initial slopes of the radiation decay curves. For the 30‐torr data, a unimolecular rate constant fit to the data is keff = 2.1 × 1011exp(− 39 200 / T) sec−1. The data are analyzed in the light of several modern unimolecular rate theo...

Shock tube studies on Fe(CO)5 + O2: 11 μ FeO emission and kinetics

Abstract Shock-tube experiments to measure the gas phase FeO fundamental vibration-rotation radiative band intensity at 11.5 μ have been performed. In measurements behind incident shocks, equilibrium amounts of FeO formed quickly, and CO2 formation occured more quickly in the presence of Fe and FeO than can be understood on the basis of previous studies of CO + O2 induction times. Measurements with a calibrated optical system at 10.4–16.3 μ wavelength yielded an integrated band intensity for FeO of 450 ama−1 cm−2 ± 32% (2σ limits). A bound for the rate of the reaction Fe + O2→FeO + Ok ⩾ 5 x 10−12 cm3 molecule−1 sec−1 for T = 2400°K is given and a possible mechanism relating FeO to the rapid CO2 formation is discussed.

Excitation Mechanism for the O2 Schumann–Runge System

The Schumann–Runge band system of O2 involving transitions between the X 3Σg− ground state and the B 3Σu− excited state has been the subject of many investigations which have shown that the radiating state is strongly coupled to the O atoms and that the population mechanism is very fast. In the present study, the emitted radiation was monitored with filter–photomultiplier combinations as a function of time behind incident shock waves in O2, O2–Ar, and O2–Ne mixtures at wavelengths centered at 2300 and 3250 A. Initial pressures in the shock tube were 1–100 torr and the (equilibrium) temperature range was 2800–5300°K. The radiation, subsequent to a short incubation time, rose monotonically to a plateau level given for each of the two channels by I2300 = 4.4 × 10−36[exp(− 20.3 × 103 / T)](O)2 and I3250 = 1.1 × 10−36[exp(− 11.3 × 103 / T)](O)2 in watts/cubic centimeters·steradians·microns where (O) is the number of O atoms per cubic centimeter. These results are in disagreement with the results of Myers and B...

Shock Front Structure in O2 at High Mach Numbers

Shock structure measurements were made on O2 in a 24‐in. diameter shock tube at initial pressures of 15 and 30 μ of Hg from Mach 4 to 21. An ultraviolet absorption technique using 1470‐A radiation was employed to monitor the density of O2 molecules. In order to reduce shock front curvature effects, the knife‐edge technique was employed using only a 4‐in. optical path between knife edges. The data indicate that translational and rotational degrees of freedom are excited simultaneously. At about Mach 10 vibrational excitation begins to appear in the same zone as translational and rotational excitation; by Mach 14 all these processes occur simultaneously. Around Mach 16 dissociation starts to occur in the same zone. The thickness of the shock front decreases from three ambient mean free paths at Mach 4 to 2 ambient mean free paths at Mach 10 and remains essentially constant at higher Mach numbers.