An Investigation of the D/H Addition−Elimination and H Atom Abstraction Channels in the Reaction D + H₂CO in the Temperature Range 296 K ≤T≤ 780 K

Abstract

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.

Isotope effects for formaldehyde plus hydrogen addition and abstraction reactions: rate calculations including tunnelling

“…In Table 1 the vibrational adiabatic barriers, which incorporate zeropoint vibrational energies, are reported for the gas phase H + H 2 CO, D + H 2 CO and H + D 2 CO addition and abstraction reactions and the D + D 2 CO addition reaction. The calculated vibrational adiabatic barriers for H and D addition to H 2 CO (2318, 2204 K) are in reasonable agreement with estimates of 2216 ± 216 and 1957 ± 144 K from gas phase experiments combined with unimolecular rate theory (Oehlers et al 2000). Likewise, the high-temperature gas phase results from Oehlers et al (2000) show that abstraction is preferred over addition for the reaction of H and D atoms with H 2 CO, in agreement with our calculated vibrational adiabatic barriers.…”

Ab Initio Chemical Kinetics for the CH3 + O(3P) Reaction and Related Isomerization–Decomposition of CH3O and CH2OH Radicals

“…The rate constant curve predicted by CVT/SCT is in good agreement with most of the experimental data. In the high-temperature range, the theoretical values have a larger deviation from the results reported by Cribb et al 32 and Oehlers et al, 35 For practical applications, the predicted rate constants for this H-abstraction channel have been fitted by least-squares analysis and are given below in units of cubic centimeters per molecule per second for the temperature range of 200−3000 K: where k is rate constant, α branching ratio, and M the inert gas molecule. The formation of CH 2 OH is influenced by not only k 1 but also k 2 because of the isomerization between CH 2 OH and CH 3 O, similarly for the formation of CH 3 O.…”

“…The barriers of the forward and reverse hydrogen atom abstraction reactions are predicted to be 6.1 and 22.5 kcal/mol, respectively, which are almost the same as those calculated at the G2M//B3LYP/6-311+G(3df,2p) level. In 2000, Oehlers et al 35 gave the forward reaction activation energy of 4.4 ± 0.4 kcal/mol by analyzing their kinetic results in the temperature range of 296−780 K. Two years later, another The Journal of Physical Chemistry A Article direct measurement of the reaction by Friedrichs et al 36 determined the activation energy to be 9.7 kcal/mol for the temperatures from 1510 to 1960 K. Recently, Wang et al 37 have located a transition state for the H-abstraction process at the CCSD(T)-F12/VTZ-F12 level to be 6.4 kcal/mol, which is close to our values of 6.1 kcal/mol. The energy of CHO + H 2 relative to that of CH 2 O + H was predicted to be −16.4 and −16.1 kcal/mol at the CCSD(T) and G2M levels, respectively, which agree quantitatively with the heat of reaction, −16.5 ± 0.2 kcal/mol, calcualted by the heats of formation of the related species (Δ f H°0(CHO) = 10.0 kcal/mol 69 and others in Table 3).…”

Photodissociation Spectroscopy of Zn+−Formaldehyde

“…[3][4][5] For H + H 2 CO reactions, recent experiments suggest that abstraction and addition-elimination pathways are competitive. 6 For transition-metal reactions with formaldehyde, recent crossed molecular beam studies (and subsequent ab initio modeling calculations) have found that the reaction Y + H 2 CO proceeds through a multistep insertion process: 7,8 Studies of the chemical interactions of group II metal ions with H 2 CO are interesting because, as with H-atoms, multiple reaction pathways might be open. In addition, Mg + -and Ca + -H 2 CO chemistry may be important in the organic chemistry of the interstellar medium.…”