THE KINETICS AND CHEMILUMINESCENCE OF OZONE - AROMATIC REACTIONS IN THE GAS PHASE.

摘要

The gas phase reactions of ozone with benzene, toluene, paraxylene, meta-xylene, and ortho-xylene were studied in the temperature range 25(DEGREES)C - 150(DEGREES)C. The rate law found for benzene was -d{lcub}O(,3){rcub}/dt = k(,1){lcub}O(,3){rcub}{lcub}B{rcub} + k(,a){lcub}O(,3){rcub}('2){lcub}B{rcub}/(1 + k(,b){lcub}B{rcub}). The rate expression for the other aromatics was -d{lcub}O(,3){rcub}/dt = k(,1){lcub}O(,3){rcub}{lcub}A{rcub} + k(,2){lcub}O(,3){rcub}('2). The benzene rate law reduced to that for the other aromatics at higher benzene pressure. A low ozone pressure upturn in the primary and secondary rate constants was observed in all systems. Added CO(,2) had no effect on this upturn and added C(,2)F(,6) partially suppressed the upturn in the primary rate constant, leaving the secondary rate constant unchanged. Added O(,2) had no effect in the first rate law term but suppressed the second term by a factor of 10 implying a bimolecular primary process followed by a chain quenched by O(,2).; Arrhenius parameters were determined and for the primary rate constants (in cm('3) molecule('-1) s('-1)) were:(UNFORMATTED TABLE FOLLOWS); 1n k(,1)(Ben) = 19.1 (+OR-) 1.2 - 12000 (+OR-) 900/T; 1n k(,1)(Tol) = 13.0 (+OR-) 1.0 - 7600 (+OR-) 700/T; 1n k(,1)(P-X) = 14.7 (+OR-) 1.1 - 8200 (+OR-) 600/T; 1n k(,1)(M-X) = 15.4 (+OR-) 1.1 - 8300 (+OR-) 600/T; 1n k(,1)(O-X) = 14.7 (+OR-) 1.0 - 8000 (+OR-) 600/T.(TABLE ENDS); Rate constants and Arrhenius parameters obtained in this work were compared with the few, scattered literature values. Thermodynamic values obtained from the Arrhenius parameter compared favorably with those calculated using group additivity. Linear free energy comparisons with the reactions of aromatic with O (('3)P) and OH indicate that the initial attack by ozone on the aromatic ring is electrophilic in nature.; All five aromatic - ozone systems gave similar weak chemiluminescence. The emission was identified as follows: a peak at 310 nm consistent with OH (A('2)(SIGMA)('+)(--->)X('2)(PI)); a peak at 430 nm consistent with CH (A('2)(DELTA)(--->)X('2)(PI)); bands at 510 - 530 nm consistent with electronically excited (alpha)-dicarbonyls; Meinel bands at 550 - 800 nm due to OH (X('2)(PI)(,i), (nu) (LESSTHEQ) 9). Possible channels for the production of these species were discussed.