O 2 Vibration Relaxation in Oxygen-Argon Mixtures

Abstract

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.

Transient Phenomena in Dissociation of Diatomic Molecules

“…The computed values are in excellent agreement with the experimental results over the range 2900 to 7200 OK. These incubation times are three to four times longer than Camac's relaxation times (22). Our calculations indicate that up to17200 OK, the time at which the rate of formation of oxygen atoms settles down to a steady value corresponds to practically complete relaxation (Fig.…”

“…Therefore, the vibrational relaxation (22) and dissociation (1, 6) may be conveniently studied independently of one another, and observable incubation times occur. At higher temperatures, however, considerable dissociation-relaxation coupling is observed (I).…”

“…For the case of 0, dilute in argon, vibrational relaxation times and molecular extinction coefficients at 1470 A have been measured (22) over the temperature range of interest. The values of k,,,, were obtained from recent low-temperature recombination rate constants (23) and the results obtained by Wray (24), who studied recombination of atoms in shock-dissociated ozone.…”

“…The vibrational relaxation time of C1, in Ar, .c,(Cl,-Ar), was calculated using the method described elsewhere (28). Vibrational relaxation times needed for these calculations are available in the literature (22,29). Although r,(Cl,-Ar) has not been measured, and thus cannot be compared to z,(Cl,-Ar) presently calculated, the value obtained is not unreasonable; furthermore the method (28) predicts .c,(Cl,-He) in good agreement with experiment (30).…”

A SHOCK TUBE STUDY OF THE COUPLING OF THE 02-Ar RATES OF DISSOCIATION AND VIBRATIONAL RELAXATION

“…For the vibrational relaxation time, Tv, of 02 by Ar, Camac 2 give s -7167 131 l/rv=l. 2xlO -T I / 6 l-exp(-2228/T)I exp(-l. 04xl07/T)3n Ar sec-.…”