Temperature and Pressure Dependent Rate Coefficients for the Reaction of Ketene with Hydroxyl Radical

The
reaction of ketene with hydroxyl radical is drawing growing
attention, for it is found to constitute an important step during
the combustion of hydrocarbon and oxygenated hydrocarbon fuels, e.g.,
acetylene, propyne, allene, acetone, gasoline, diesel, jet fuels,
and biofuels. We studied the potential energy surface (PES) of this
reaction using B2PLYP-D3/cc-PVTZ for geometry optimization and composite
methods based on CCSD­(T)-F12/cc-PVTZ-F12 for energy calculations.
From this PES, temperature- and pressure-dependent rate coefficients
and branching ratios at 200–3000 K and 0.01–100 atm
were derived using the RRKM/ME approach. The reaction is dominated
by four product channels: (i) OH addition on the olefinic carbon of
ketene to form CH2OH + CO, which is the most dominant under
all conditions; (ii) H abstraction producing HCCO + H2O,
which is favored at high temperatures; (iii) OH addition on the carbonyl
carbon to form CH3 + CO2, which is favored at
low pressures and high temperatures; and (iv) collisional stabilization
of CH2COOH, which is favored at high pressures and low
temperatures. With increasing temperatures, the overall rate constant koverall exhibit first negative but then positive
temperature dependency, with its switching point (also the minimum
point) at ∼400 K. Both product channel CH2OH + CO
and HCCO + H2O are independent of pressure, whereas formation
of CH3 + CO2 and collisional stabilization of
CH2COOH are highly pressure dependent. Fitted modified
Arrhenius expressions of the calculated rate constants are provided
for the purpose of combustion modeling.