Reaction of O(3P) with C2H4: Yield of the Reaction Products as a Function of Temperature

Experimental Study of the Reaction of O(3P) with Carbonyl Sulfide between 220 and 960 K

The reaction of a ground-state O atom with carbonyl sulfide is of interest for atmospheric (stratosphere and hot near-source volcanic plume) and combustion chemistry. In the present work, we employed a discharge-flow system combined with a modulated molecular beam mass spectrometry technique to measure the rate constant and products of the O + OCS reaction. The overall rate constant was determined either from the kinetics of the reaction product, SO radical, formation or under pseudo-first-order conditions from the decays of OCS in an excess of oxygen atoms: k₁ = 1.92 × 10^-12 × (T/298)^2.08 exp(-1524/T) cm³ molecule^-1 s^-1 at T = 220-960 K, with conservative uncertainty of 20%. The yield of another reaction product, CO₂, was found to increase from 3.55% at T = 455 K to 14.2% at T = 960 K, resulting in the following Arrhenius expression for the rate constant of the minor (S + CO₂ forming) reaction channel: k_1b = 4.19 × 10^-11 exp(-4088/T) cm³ molecule^-1 s^-1 at T = 455-960 K (with an uncertainty of 25%). The kinetic and mechanistic data from the present work are discussed in comparison with previous experimental and computational studies.

The reaction of O(3P) with alkynes: a dynamic and computational study focusing on formyl radical production

Production of formyl radical, HCO, from reactions of O(³P) with alkynes (acetylene, propyne, 1-butyne, and 1-pentyne) has been investigated using cavity ringdown laser absorption spectroscopy (CRDLAS) and computational methods. No HCO was detected from reaction with acetylene, while the amount of HCO increased for propyne and 1-butyne, dropping off somewhat for 1-pentyne. These results differ from trends previously observed for reactions of O(³P) with alkenes, which exhibit the largest HCO production for the smallest alkene and drop off as the alkene size increases. Computational studies employing density functional and coupled cluster methods have been employed to investigate the triplet and singlet state pathways for HCO production. Because intersystem crossing (ISC) has been shown to be important in these processes, the minimum energy crossing point (MECP) between the triplet and singlet surfaces has been studied. We find the MECP for propyne to possess C₁ symmetry and to lie lower in energy than previous studies have found. Natural Bond Orbital and Natural Resonance Theory analyses have been performed to investigate the changes in spin density and bond order along the reaction pathways for formation of HCO. Explanations are suggested for the trend in HCO formation observed for the alkynes. The trend in alkyne HCO yield also is compared and contrasted with the trend previously observed for the alkenes.

Reaction of O(3P) with C3H6: Yield of the Reaction Products as a Function of Temperature

Reaction of oxygen atoms with propene is an important step in combustion processes particularly affecting the profiles of intermediate species and flame speed. The relative importance of different pathways of this multichannel reaction at different temperatures represents significant theoretical interest and is essential for modeling combustion systems. In the present work, we report the first experimental investigation of the products of the O(³P) + C₃H₆ reaction over an extended temperature range (298-905 K). By using a low pressure flow reactor combined with a quadrupole mass spectrometer, the yields of the five reaction products, H atom, CH₃, C₂H₅, CH₂O and OH were determined as a function of temperature between 298 and 905 K: 0.0064 × (T/298)^2.74 exp(765/T), 1.41 × (T/298)^-1.0 exp(-335/T), 0.92 × (T/298)^-1.41 exp(-381/T), 0.17 × (T/298)^0.165 exp(-36/T), and 0.0034 × (T/298)^2.34 exp(788/T), respectively (corresponding to the variation of the respective yields between 298 and 905 K in the ranges 0.08-0.31, 0.46-0.32, 0.26-0.12, 0.15-0.19, and 0.05-011), independent of pressure in the range 1-8 Torr of helium. For the yields of the minor reaction products, H₂ and CH₃CHO the upper limits were determined as 0.2 and 0.05, respectively. These results are compared with the experimental data and theoretical calculations available in the literature.

Crossed beam polyatomic reaction dynamics: recent advances and new insights

This review summarizes the developments in polyatomic reaction dynamics, focusing on reactions of unsaturated hydrocarbons with O-atoms and methane with atoms/radicals.