The Thermal Decomposition of Ozone in a Shock Tube

Abstract

The thermal decomposition of ozone in argon and nitrogen inert gases has been studied in a shock tube. The important reactions are R 1 and R3. R1, R2 R3 M + 0,j .% M -/ -0 2 + 0 0 + 0 3 --+ 0 2 + 0 2 I n the concentration and temperature range studied-argon 0.00334 to 0.0264 mole/l., 769 to 910°K.; nitrogen 0,00902 to 0.01286 mole/l., 689 to 863"K-Rl is a unimolecular reaction a t its low pressure second order limit with k l N t / k l A = kaNr/ kz.4 = 1.64 & 0.1'7. Combining the shock tube data for M = NZ with data in the range 303 t o 383'K.. due to Glissman and Schumacher and reinterpreted by Benson and Axworthy, gives k1y2 = (5.8 f 0.6) X 10" exp( -23,150 Z!C 300/RT)(mole/ L)-l sec.-l and k2x2 = (9.4 i 1 ) X lofi exp(f1700 =I= 300/RT) = 2.0 X lo7 (1000/T)1~66(mole/l.)-2 sec.-l. The kl d a t a are discussed in terms of the Slater and Hinshelwood-Rice-Ramsperger-Kassel ( H R R K ) theories. Interpretation of the data by the classical H R R K theory gives 2.83 =k 0.2 effective oscillators and a collision efficiency of 0.039. The values of k3 obtained are consistent with an extrapolation of previous low temperature data. Vibrationally excited oxygen molecules with from 10 t o 17 vibrational quanta, produced by the strongly exothermic R3 involving O( 3P) atoms, were detected by flash absorption spectra.Introduction Several investigations have been made of the thermal decomposition of ozone, from slightly above room temperature to 5GS'K. Without attempting a discussion of all this work3 and of the evolution of thought regarding the mechanism, we follow Benson and Axworthy4 in accepting reactions R1, R2 and R3 as providing a satisfactory explanation of the homogeneous thermal decomposition. Reaction R4 is included, although it is unimportant in all previous work and in the present work.

Thermal Decomposition of Ozone

“…This confirms that the reaction is indeed a unimolecular reaction in the low pressure limit and is in agreement with the conclusion of Benson and Axworthy2 and Jones and Davidson. 4 The solid line in Fig. 2 is a theoretical estimate based on the HRRKM (Hinshelwood, Rice, Ramsperger, Kassel, Marcus) theory21 in its low-pressure limit.…”

“…2 The reaction has also been studied in the temperature range, 770-91O o K, in shock waves by Jones and Davidson. 4 These authors have determined the value of kl to be 5.8XlO 11 exp(-23150/RT) liter/mole· sec where M is N2 from the combination of their data and that of Benson and Axworthy.2 An alternate expression (where M is N 2 ) which correlates well with the Hinshelwood, Rice, Ramsperger, and Kassel theory (HRRK) with s=2.75 is In their studies, Reaction (-1) is negligible but they have reanalyzed k_l from Benson and Axworthy and find it to be 9.4X10 6 exp(+1700/RT) liter 2 /mole 2 ·sec. They have also found for Reaction (2) that k2=2.96XlOlO exp(-5600/RT) liter/mole· sec is consistent with their data.…”

Global ozone balance in the natural stratosphere

“…Rate constants, k, including values from 1906 to 1972, for e reaction e are given in Figure 16 [ Davis et al, 1973a;McCrumb and Kaufman, 1972;Krezenski et al, 1971;Jones and Davidson, 1962;Garvin, 1954;Jahn, 1906;Glissmen and Schumacher, 1933]. The line through the points was used in these calculations, except when ke was varied as a sensitivity test.…”

“…Kaufman and Kelso, 1967;temperature, Johnston, 1968. , Kkreverse' high + McCrumb and Kaufman, 1972; ~. Krezenski and Heicklen, 1971; 0, Jones and Davidson, 1962;V, Garvin, 1954;¢, Jahn, 1906;Glissman and Schumacher, 1933. .....…”

Neutral reactions involving oxygen and nitrogen

“…If, however, a value of E, = -1.7 is used, E, is reduced to 4.9. The shock tube data by Davidson and Jones have been interpreted (46) to give k, = 5.7 but more recent shock tube work suggests this value is too high (49).…”