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Title: Crossed beam reactions of methylidyne [CH(X-2 Pi)] with D2-acetylene [C2D2(X-1 Sigma(+)(g))] and of D1-methylidyne [CD(X-2 Pi)] with acetylene [C2H2(X-1 Sigma(+)(g))]
Journal: Phys. Chem. Chem. Phys.
Volume: 14
Page(s): 575 - 588
Year: 2012
Reference type: Journal article
Squib: 2012KAI/GU,575-588
Reaction:
C2H2 + CD → Products
Reaction order:
2
Rate expression:
no rate data available
Category: Experiment
Data type:
Mechanistic information only
Pressure dependence:
None reported
Experimental procedure:
Molecular beam
Excitation technique:
Flash photolysis (laser or conventional)
Time resolution:
By end product analysis
Analytical technique:
Mass spectrometry
Comments:
The crossed molecular beam reactions of ground state methylidyne, CH, with D2-acetylene, C2D2, and of D1-methylidyne, CD, with acetylene, C2H2, were conducted under single collision conditions at a collision energy of 17 kJ/mol. Four competing reaction channels were identified in each system following atomic ‘hydrogen’ (H/D) and molecular ‘hydrogen’ (H2/D2/HD) losses. The reaction dynamics were found to be indirect via complex formation and were initiated by two barrierless-addition pathways of methylidyne/D1-methylidyne to one and to both carbon atoms of the D2-acetylene/acetylene reactant yielding HCCDCD/DCCHCH and c-C3D2H/c-C3H2D collision complexes, respectively. The latter decomposed via atomic hydrogen/deuterium ejection to form the thermodynamically most stable cyclopropenylidene species (c-C3H2, c-C3D2, c-C3DH). On the other hand, the HCCDCD/DCCHCH adducts underwent hydrogen/deuterium shifts to form the propargyl radicals (HDCCCD, D2CCCH; HDCCCH, H2CCCD) followed by molecular ‘hydrogen’ losses within the rotational plane of the decomposing complex yielding l-C3H/l-C2D. Quantitatively, the studies suggest a dominating atomic compared to molecular ‘hydrogen’ loss. No thermal rate constants were obtained.
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