Julien Morin

Experimental study of the reactions of limonene with OH and OD radicals: kinetics and products.

The kinetics of the reactions of limonene with OH and OD radicals has been studied using a low-pressure flow tube reactor coupled with a quadrupole mass spectrometer: OH + C10H16 → products (1), OD + C10H16 → products (2). The rate constants of the title reactions were determined using four different approaches: either monitoring the kinetics of OH (OD) radicals or limonene consumption in excess of limonene or of the radicals, respectively (absolute method), and by the relative rate method using either the reaction OH (OD) + Br2 or OH (OD) + DMDS (dimethyl disulfide) as the reference one and following HOBr (DOBr) formation or DMDS and limonene consumption, respectively. As a result of the absolute and relative measurements, the overall rate coefficients, k1 = (3.0 ± 0.5) × 10(-11) exp((515 ± 50)/T) and k2 = (2.5 ± 0.6) × 10(-11) exp((575 ± 60)/T) cm(3) molecule(-1) s(-1), were determined at a pressure of 1 Torr of helium over the temperature ranges 220-360 and 233-353 K, respectively. k1 was found to be pressure independent over the range 0.5-5 Torr. There are two possible pathways for the reaction between OH (OD) and limonene: addition of the radical to one of the limonene double bonds (reactions 1a and 2a ) and abstraction of a hydrogen atom (reactions 1b and 2b ), resulting in the formation of H2O (HOD). Measurements of the HOD yield as a function of temperature led to the following branching ratio of the H atom abstraction channel: k2b/k2 = (0.07 ± 0.03) × exp((460 ± 140)/T) for T = (253-355) K.

Thermal Decomposition of Isopropyl Nitrate: Kinetics and Products

Kinetics and products of the thermal decomposition of isopropyl nitrate (IPN, C3H7NO3) have been studied using a low pressure flow reactor combined with a quadrupole mass spectrometer. The rate constant of IPN decomposition was measured as a function of pressure (1-12.5 Torr of helium) and temperature in the range 473-658 K using two methods: from kinetics of nitrate loss and those of reaction product (CH3 radical) formation. The fit of the observed falloff curves with two parameter expression [Formula: see text] provided the following low and high pressure limits for the rate constant of IPN decomposition: k0 = 6.60 × 10-5exp(-15190/T) cm3 molecule-1 s-1 and k∞ = 1.05 × 1016 exp(-19850/T) s-1, respectively, which allows one to determine (via the above expression) the values of k1 (with 20% uncertainty) in the temperature and pressure range of the study. It was observed that thermal decomposition of IPN proceeds through initial breaking of the O-NO2 bond, leading to formation of NO2 and isopropoxy radical (CH3)2CHO, which rapidly decomposes forming CH3 and acetaldehyde as final products. The yields of NO2, CH3, and acetaldehyde upon decomposition of isopropyl nitrate were measured to be (0.98 ± 0.15), (0.96 ± 0.14), and (0.99 ± 0.15), respectively. In addition, the kinetic data were used to determine the O-NO2 bond dissociation energy in isopropyl nitrate, 38.2 ± 4.0 kcal mol-1.

Gas-Phase Reaction of Hydroxyl Radical with p-Cymene over an Extended Temperature Range

The kinetics of the reaction of OH radicals with p-cymene has been studied in the temperature range of 243-898 K using a flow reactor combined with a quadrupole mass spectrometer: OH + p-cymene → products. The reaction rate constant was determined as a result of absolute measurements, from OH decay kinetics in excess of p-cymene and employing the relative rate method with OH reactions with n-pentane, n-heptane,1,3-dioxane, HBr, and Br2 as the reference ones. For the rate coefficient of the H atom abstraction channel, the expression k1b = (3.70 ± 0.42) × 10(-11) exp[-(772 ± 72)/T] was obtained over the temperature range of 381-898 K. The total rate constant (addition + abstraction) determined at T = 243-320 K was k1 = (1.82 ± 0.48) × 10(-12) exp[(607 ± 70)/T] or, in a biexponential form, k1 = k1a + k1b = 3.7 × 10(-11) exp(-772/T) + 6.3 × 10(-13) exp(856/T), independent of the pressure between 1 and 5 Torr of helium. In addition, our results indicate that the reaction pathway involving alkyl radical elimination upon initial addition of OH to p-cymene is most probably unimportant.

Reaction of Limonene with F2: Rate Coefficient and Products

The kinetics of the reaction of limonene (C10H16) with F2 has been studied using a low pressure (P = 1 Torr) and a high pressure turbulent (P = 100 Torr) flow reactor coupled with an electron impact ionization and chemical ionization mass spectrometers, respectively: F2 + Limonene → products (1). The rate constant of the title reaction was determined under pseudo-first-order conditions by monitoring either limonene or F2 decay in excess of F2 or C10H16, respectively. The reaction rate constant, k1 = (1.15 ± 0.25) × 10(-12) exp(160 ± 70)/T) was determined over the temperature range 278-360 K, independent of pressure between 1 (He) and 100 (N2) Torr. F atom and HF were found to be formed in reaction 1 , with the yields of 0.60 ± 0.13 and 0.39 ± 0.09, respectively, independent of temperature in the range 296-355 K.