Investigation of the High Temperature Reaction of Hydrogen Atoms with Phenylacetylene

Abstract

The reaction of C₆H₅ − C₂H + H has been investigated at elevated temperatures in the postshock region behind reflected shocks. The thermal decomposition of very small amounts (1 – 3 ppm) of C₂H₅I served as a source for H-atoms. Atomic resonance absorption spectrometry (ARAS) was applied to measure simultaneously H-atom and I-atom profiles. The experiments covered the temperature range from 1190 to 1560 K at total pressures of 2.3·10⁵± 0.2·10⁵ Pa. A rate coefficient of

$${k_{1.1}} = 3.0 \cdot {10^{14}}{T^{ - 0.48}}{e^{ - 700/T}}\,c{m^3}mo{l^{ - 1s - 1}}$$

is obtained for the reaction

$${C_6}{H_5} - {C_2}H + H \to \,{\rm{Products}}$$

(1.1)

From the available thermochemical data two product channels are plausible:

$${C_6}{H_5} - {C_2}H + H \to {C_6}{H_5} + {C_2}{H_2},{\Delta _R}H_{298}^0$$

(1.1a)

$${C_6}{H_5} - {C_2}H + H \to {C_6}{H_4} + {C_2}H + {H_2},{\Delta _R}H_{298}^0 = 6.3kcalmo{l^{ - 1}}$$

(1.1b)

The main product channel at elevated temperatures is route 1.1a. Detailed evaluation of existing thermodynamic data enables the calculation of an equilibrium constant for reaction 1.1a. From this and the rate coefficient for reaction 1.1a a rate coefficient

$${k_{1.2}} = 2.7 \cdot {10^8}{T^{0.7}}{e^{ + 1800/T}}\,c{m^3}mo{l^{ - 1}}{s^{ - 1}}$$

for the reaction of phenyl radicals with acetylene

$${C_6}{H_5} + {C_2}{H_5} \to {C_6}{H_5} - {C_2}H + H$$

(1.2)

is obtained which is in good agreement with recent results from Fahr et al [1.1]. Reaction 1.2 is an important process in sooting flames.