The reactions of H and D atoms with H2CO (H + H2CO → H2 + HCO (1.1), D + H2CO → HD + HCO (2.1), and D + H2CO → H + HDCO (2.2)) have been studied in the temperature range 296 K ≤ T ≤ 780 K in an isothermal discharge flow reactor with EPR detection of D and H atoms and LIF detection of HCO. Simultaneous measurements of the absolute concentration−time profiles of the three species established the occurrence of the D/H isotope exchange reaction (2.2) in addition to the H atom abstraction channel (2.1). The rate constants for the three reactions could be represented by the Arrhenius expressions k 1.1(T) = (8.7 ± 1.9) × 1012 exp[−(14.5 ± 0.7) kJ mol-1/RT] cm3 mol-1 s-1, k 2.1(T) = (1.2 ± 0.5) × 1013 exp[−(15.8 ± 0.8) kJ mol-1/RT] cm3 mol-1 s-1, and k 2.2(T) = (5.9 ± 1.5) × 1012 exp[−(14.7 ± 1.0) kJ mol-1/RT] cm3 mol-1 s-1. A mechanistic analysis of reaction 2.2 using the unimolecular rate theory gave these estimates for the classical potential energy barrier heights in the addition of D and H atoms to H2CO:  ΔE 0(D + H2CO) = 1360 ± 100 cm-1 and ΔE 0(H + H2CO) = 1540 ± 150 cm-1.

The kinetics of the chlorination equilibrium of methanol, CH2OH + HCl ⇋ CH3OH + Cl (1, – 1), have been studied using the fast flow technique with Laser Magnetic Resonance and Electron Paramagnetic Resonance detection. The rate constants of the forward and reverse reactions were found to be k1 = (2.3±0.9) ·1011 exp [‐(20.9±2.9) kJ·mol−1/RT] cm3/mol·s in the temperature range 500 K≤T≤812 K and k‐1 = (3.7±0.4)±1013 cm3/mol·s at room temperature. These kinetic results were utilized in third law and second law procedures to obtain the value of the heat of formation of the hydroxymethyl radical. The entropy of CH2OH, S0f,298(CH2OH) = (254±4) J/mol·K, and the activation energy of reaction (‐1), E‐1 = (0±4) kJ/mol, which are required for the calculations, were selected by critical assessment of the available literature data. The average of the third law and second law determinations provided SfH0298(CH2OH) = ‐(9±6) kJ/mol. This value is higher by 17 kJ/mol than the heat of formation value in common use and implies a stronger C – H bond energy in methanol, D298(H–CH2OH) = 410 kJ/mol. These new thermochemical quantities are in excellent agreement with the very recent recommendations of Seetula and Gutman [J. Phys. Chem. 96, 5401 (1992)] and have important implications for modeling studies of complex chemical systems such as the combustion of methanol.

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Kinetics of the reactions H (D) + CHPOH (CD20D) were studied at room temperature using the fast flow technique coupled with laser magnetic resonance and electron paramagnetic resonance detections. Rate coefficients of 4.1 f 0.8, 8.1 f 1.1, and 4.8 f 1.6 (in cm3 mol-' s-l units) were determined for the overall reactions H + CHZOH -products (l), D + CHzOH -products (2), and D + CD20D -products (3), respectively. Branching ratios for OH formation were found to be 25 f 5% in reaction 1 and 23 f 10% in reaction 2. Formation of H atoms by H/D isotope exchange was found to account for %12% of reaction 2. On the basis of the kinetic results and simple theoretical considerations, the reaction between H atoms and hydroxymethyl radicals was suggested to occur to about 70% via direct disproportionation leading to formaldehyde formation and to about 30% via indirect mechanism through complex (CH30H)*. Under the conditions used, CH3 and OH were shown to be the products of the major channel of the complex-forming reaction path. Results determined for reaction H + CH20H are compared with those obtained previously for H + CH3O. Implications for combustion systems are discussed briefly.

The rate constants for the reactions HCO+H → products (1) and HCO+D → products (2) were determined at room temperature in an isothermal discharge flow reactor. Atom and radical concentrations in the reactions were monitored using Electron Paramagnetic Resonance (EPR) for H and D atoms and Far Infrared Laser Magnetic Resonance (FIR‐LMR) and Laser Induced Fluorescence (LIF) for HCO. The overall rate constants describing the decay of the HCO concentrations with H and D, respectively, were found to be k1=(6.8±2.0)×1013 cm3 mol−1 s−1 and k2=(8.3±2.5)×1013 cm3 mol−1 s−1. The results are discussed assuming a mechanism that allows for parallel reaction pathways via a direct H atom abstraction reaction or via an addition‐elimination reaction through a short‐lived highly vibrationally excited formaldehyde complex.