Issue 21, 2014

Dynamics of the O(3P) + C2H2 reaction from crossed molecular beam experiments with soft electron ionization detection

Abstract

The reaction between ground state oxygen atoms, O(3P), and the acetylene molecule, C2H2, has been investigated in crossed molecular beam experiments with mass-spectrometric detection and time-of-flight analysis at three different collision energies, Ec = 34.4, 41.1 and 54.6 kJ mol−1. From product angular and velocity distribution measurements of the HCCO and CH2 products in the laboratory frame, product angular and translational energy distributions in the center-of-mass frame were determined. Measurements on the CH2 product were made possible by employing for product detection the recently implemented soft electron-ionization (EI) technique with low-energy, tunable electrons, which has permitted suppressing interference coming from the dissociative ionization of reactants, products and background gases. It has been found that the title reaction leads only to two competing channels: H + HCCO (ketenyl) and CO + CH2 (triplet methylene). The branching ratio of cross sections between the two competing channels has been determined to be σ(HCCO)/[σ(HCCO) + σ(CH2)] = 0.79 ± 0.05, independent of collision energy within the experimental uncertainty. This value is in line with that obtained in the most recent and accurate kinetics determination at room temperature as well as with that predicted from recent theoretical calculations based on statistical rate theory and weak-collision master equation analysis and on dynamics surface-hopping quasiclassical trajectory calculations on-the-fly on coupled triplet/singlet ab initio potential energy surfaces. The firm assessment of the branching ratio as a function of translational energy for this important reaction, besides its fundamental significance, is of considerable relevance for the implementation of theoretical models of hydrocarbon combustion.

Graphical abstract: Dynamics of the O(3P) + C2H2 reaction from crossed molecular beam experiments with soft electron ionization detection

Article information

Article type
Paper
Submitted
08 11 2013
Accepted
14 1 2014
First published
15 1 2014

Phys. Chem. Chem. Phys., 2014,16, 10008-10022

Dynamics of the O(3P) + C2H2 reaction from crossed molecular beam experiments with soft electron ionization detection

F. Leonori, N. Balucani, G. Capozza, E. Segoloni, G. G. Volpi and P. Casavecchia, Phys. Chem. Chem. Phys., 2014, 16, 10008 DOI: 10.1039/C3CP54729A

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