Reaction of hydrogen atoms with propyne at high temperatures: An experimental and theoretical study

Tobias Bentz, Binod R. Giri, Horst Hippler, Matthias Olzmann*, Frank Striebel, Milan Szöri

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

34 Scopus citations


The kinetics of the reaction of hydrogen atoms with propyne (pC 2H4) was experimentally studied in a shock tube at temperatures ranging from 1200 to 1400 K and pressures between 1.3 and 4.0 bar with Ar as the bath gas. The hydrogen atoms (initial mole fraction 0.5-2.0 ppm) were produced by pyrolysis of C2H5I and monitored by atomic resonance absorption spectrometry under pseudo-first-order conditions with respect to propyne (initial mole fraction 5-20 ppm). From the hydrogen atom time profiles, overall rate coefficients kov ≡= -([pC 3H4][H]-1 × d[H]/dt for the reaction H + pC3H4 → products (≠ H) were deduced; the following temperature dependence was obtained: kov = 1.2 × 10 -10 exp(-2270 K/T) cm3 -1 with an estimated uncertainty of ±20%. A pressure dependence was not observed. The results are analyzed in terms of statistical rate theory with molecular and transition state data from quantum chemical calculations. Geometries were optimized using density functional theory at the B3LYP/6-31G(d) level, and single-point energies were computed at the QCISD(T)/cc-pVTZ level of theory. It is confirmed that the reaction proceeds via an addition-elimination mechanism to yield C 2H2 + CH3 and via a parallel direct abstraction to give C3H3 + H2. Furthermore, it is shown that a hydrogen atom catalyzed isomerization channel to allene (aC 3H4), H + pC3H4 → aC 3H4 + H, is also important. Kinetic parameters to describe the channel branching of these reactions are deduced.

Original languageEnglish (US)
Pages (from-to)3812-3818
Number of pages7
JournalJournal of Physical Chemistry A
Issue number19
StatePublished - May 17 2007
Externally publishedYes

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry


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