Kinetic Studies of the Thermal Decomposition of Methylperoxynitrate and of Ozone-Olefin Reactions.

This research concerns the thermal decomposition kinetics of CH(,3)O(,2)NO(,2) and laboratory kinetic measurements of ozone-olefin reactions. In the first system, the thermal decomposition rate of CH(,3)O(,2)NO(,2) was studied in the temperature range of 256-268 K at (TURN)350 torr total pressure and in the pressure range of 50-720 torr at 263 K by the perturbation of the equilibrium: (UNFORMATTED TABLE FOLLOWS). CH(,3)O(,2) + NO(,2) (+M) (DBLARR) CH(,3)O(,2)NO(,2) (+M) (3,-3). with NO. CH(,3)O(,2) + NO (--->) CH(,3)O + NO(,2) (4). (TABLE ENDS). The CH(,3)O(,2)NO(,2) was generated in situ by the photolysis of Cl(,2) in the presence of O(,2), CH(,4) and NO(,2). The decomposition kinetics were monitored in the presence of NO by the change in ultraviolet absorption at 250 nm. The Arrhenius expression obtained for the thermal decomposition is k(,-3) = 6 x 10('15) exp{-(21,000 (+OR-) 1500)/RT} sec('-1) at (TURNEQ)350 torr total pressure (mostly CH(,4)) where R = 1.987 cal/mole('-) K. The uncertainty in the Arrhenius parameters can be greatly reduced by combining this expression with data for k(,3) and thermodynamics data to give k(,-3) = (6 (+OR-) 3) x 10('15) exp{-(21,300 (+OR-) 300)/RT} sec('-1) at (TURNEQ)350 torr total pressure. Computations based on the pressure dependence of the forward reaction give k(,-3)('(INFIN)) = 2.1 x 10('16) exp{-(21,700 (+OR -) 300)/RT} sec('-1) k(,-3)('(DEGREES)) = 3.3 x 10(' -4) exp{-(20,150 x 300)/RT} cm('3) sec('-1). At 263 K the equilibrium constant K(,3,-3){263 K} is determined to be (2.68 (+OR-) 0.26) x 10('-10) cm('3). In the stratosphere the CH(,3)O(,2)NO(,2) lifetime will be controlled by play a role in the NO(,x) budget of the lower stratosphere. In the second part, the kinetics of the reactions of O(,3) with C(,2)H(,4), C(,3)H(,4), 1,3-C(,4)H(,6), and trans-1,3-C(,5)H(,8) were studied with initial olefin-to -ozone ratios (GREATERTHEQ) 4.9, in the presence of excess O(,2), and over the temperature range 232 to 300 K. The initial O(,3) pressure was varied from 5-18 mtorr, and the olefin pressure was varied from 0.1 to 4.5 torr (C(,2)H(,4)), 2.8 to 39.6 torr (allene), 52.7 to 600 mtorr (1,3-C(,4)H(,6)), or 26.2 to 106 mtorr (1,3-C(,5)H(,8)). The O(,3) decay was monitored by ultraviolet absorption. The reaction is first order in both O(,3) and olefin. The rate coefficients are independent of the O(,2) pressure (100-400 torr), and in the case of the O(,3)/C(,2)H(,4) system, the rate coefficients are independent of the nature of the diluent gas--N(,2), O(,2), and air were used. These measured rate coefficients were found to fit the Arrhenius expressions: (UNFORMATTED TABLE FOLLOWS). For C(,2)H(,4): k{232-298 K}=(7.88(+OR -)0.46)x10('-15) exp{-(5085(+OR-)580)/RT}. For C(,3)H(,4): k{252-298 K}=(1.92(+OR -)0.14)x10('-15) exp{-(5430(+OR-)830)/RT}. For 1,3-C(,4)H(,6): k{254-299 K}=(2.43(+OR -)0.15)x10('-14) exp{-(4900(+OR-)670)}. and. For t-1,3-C(,5)H(,8): k{262-298 K}=(6.56(+OR -)0.40)x10('-12). exp{-(7140(+OR-)860)/RT}. (TABLE ENDS). cm('3) s('-1), where the uncertainties represent one standard deviation.