Product State Distributions of Vibrationally Excited CO(v) for the CH(X²Π) and CH(A²Δ) Channels of the C₂H + O(³P) Reaction

Abstract

The C 2 H + O( 3 P) reaction is investigated using time-resolved Fourier transform infrared spectroscopy (TR-FTIR). The C 2 H and O radicals are produced by 193-nm photolysis of C 2 H 2 and SO 2 precursors. Multiple vibrationally excited products are observed from several resulting reaction processes, including products: CO, CO 2 , C 4 H 2 , and CH. For this choice of photolytic precursors, it is observed that the C 2 H + SO 2 , C 2 H 2 + O, and the HCCO + O reactions contribute to the observed product signals. To evaluate the contribution of the C 2 H + SO 2 reaction to the removal kinetics of C 2 H in the C 2 H 2 /SO 2 system, the room-temperature rate constant for the C 2 H + SO 2 reaction is experimentally determined to be k ) (1.1 ( 0.3) × 10 -11 cm 3 molecule -1 s -1 . The time dependencies of the CO and CO 2 species are measured experimentally and simulated to determine conditions under which contributions from the several processes that give the same product can be differentiated. Analysis of the nascent vibrational distribution of the CO products from C 2 H + O suggests the participation of both CH(A 2 ∆) and CH(X 2 Π) products, in the ratio of ∼3:2. The surprisal parameters for the vibrational distribution of the CO products of these two channels are found to be -1.5 ( 0.2 and -1.1 ( 0.2, respectively. It is suggested that the reaction proceeds through the HCCO q intermediate, in agreement with earlier studies, but the CH(A 2 ∆)/CH(X 2 Π) branching fraction may be larger than previously reported.

Deuterium kinetic isotope effects on the gas-phase reactions of C2H with H2(D2) and CH4(CD4)

“…Since the reaction of C 2 H + SO is expected to be slower than C 2 H + O( 3 P), the upper limit of k O can be estimated to be (1.15 AE 0.12) Â 10 À10 cm 3 molecule À1 s À1 . These values are in accord with the reported values k SO2 = (1.1 AE 0.3) Â 10 À11 cm 3 molecule À1 s À1 at room temperature 48 and k O = (0.9 AE 0.4) Â 10 À10 cm 3 molecule À1 s À1 estimated in a 600 K acetylene flame. 49 The measured pseudo-first order decay constant, k 1st , could be quantitatively reproduced by eqn ( 2) and (3) by using k C 2 H 2 = 1.3 Â 10 À10 cm 3 molecule À1 s À1 , 7 indicating the validity of the present assumption.…”

Kinetics of the O + ICN Reaction

“…We then used kinetic modeling to predict the time dependence of [CO] under typical experimental conditions. Table shows the mechanism used in the model; it differs from the mechanism described above in that it includes several reactions involving C 2 H chemistry. − A first-order decay of CO with a rate of 300 s –1 was included in the model to approximate the diffusion of CO molecules out of the probed volume.…”

Dynamics of the CH(A2Δ) Product from the Reaction of C2H with O2 Studied by Fourier Transform Visible Spectroscopy

“…The experimental apparatus is documented in detail in previous publications , and only a brief description is given here. The experimental setup consists of a 193 nm ArF excimer laser, a vacuum chamber, and an FT-visible spectrometer.…”