Reaction of Hydrogen Atoms with Acetylene

The reaction of hydrogen atoms with acetylene has been investigated in a fast discharge‐flow system coupled to a time‐of‐flight mass spectrometer. Isotopic studies confirm the following reaction mechanism: $$\mathrm{H}+{\mathrm{C}}_2{\mathrm{H}}_2\to {\mathrm{C}}_2{\mathrm{H}}_3^{*},$$ $${\mathrm{C}}_2{\mathrm{H}}_3^{*}\to {\mathrm{C}}_2{\mathrm{H}}_2+\mathrm{H},$$ $${\mathrm{C}}_2{\mathrm{H}}_3^{*}+\mathrm{M}\to {\mathrm{C}}_2{\mathrm{H}}_3+{\mathrm{M}}^{*},$$ $${\mathrm{C}}_2{\mathrm{H}}_3+\mathrm{H}\to {\mathrm{C}}_2{\mathrm{H}}_2+{\mathrm{H}}_2,$$ where M is a third‐body molecule and the asterisk represents chemically activated states. The pressure effect on the apparent over‐all bimolecular constant confirms that the system undergoes a unimolecular reaction according to the Rice—Ramsperger—Kassel—Marcus theory, but not to the Lindemann theory. An attempt was made to obtain the rate constants of the elementary reactions for several isotopic modifications of this system.