Proton affinity and enthalpy of formation of formaldehyde

Abstract

The proton affinity and the enthalpy of formation of the prototypical carbonyl, formaldehyde, have been determined by the first-principles composite focalpoint analysis (FPA) approach. The electronic structure computations employed the allelectron coupled-cluster method with up to single, double, triple, quadruple, and even pentuple excitations. In these computations the aug-cc-p(C)VXZ [X ϭ 2(D), 3(T), 4(Q), 5, and 6] correlation-consistent Gaussian basis sets for C and O were used in conjunction with the corresponding aug-cc-pVXZ (X ϭ 2-6) sets for H. The basis set limit values have been confirmed via explicitly correlated computations. Our FPA study supersedes previous computational work for the proton affinity and to some extent the enthalpy of formation of formaldehyde by accounting for (a) electron correlation beyond the "gold standard" CCSD(T) level; (b) the non-additivity of core electron correlation effects; (c) scalar relativity; (d) diagonal Born-Oppenheimer corrections computed at a correlated level; (e) anharmonicity of zero-point vibrational energies, based on global potential energy surfaces and variational vibrational computations; and (f) thermal corrections to enthalpies by direct summation over rovibrational energy levels. Our final proton affinities at 298.15 (0.0) K are ⌬ pa H o (H 2 CO) ϭ 711.02 (704.98) Ϯ 0.39 kJ mol Ϫ1 . Our final enthalpies of formation at 298.15 (0.0) K are ⌬ f H o (H 2 CO) ϭ Ϫ109.23 (Ϫ105.42) Ϯ 0.33 kJ mol Ϫ1 .The latter values are based on the enthalpy of the H 2 ϩ CO 3 H 2 CO reaction but supported by two further reaction schemes, H 2 O ϩ C 3 H 2 CO and 2H ϩ C ϩ O 3 H 2 CO. These values, especially ⌬ pa H o (H 2 CO), have better accuracy and considerably lower uncertainty than the best previous recommendations and thus should be employed in future studies.

Computational Study of Bond Dissociation Enthalpies for Substituted β‐O‐4 Lignin Model Compounds

“…[62,63] The CBS energies for CCSD(T) were obtained by using published formulas. [62,[64][65][66][67][68][69] Zero-point energies and thermal corrections at 298 K were added to calculate the (ROHF)MP2 and CCSD(T) BDEs. [53] 2.…”

Use of the HS-PTR-MS for online measurements of pyrethroids during indoor insecticide treatments

“…As a result, for equivalent amounts of the parent molecules, a larger quantity of protonated molecules is obtained, thus increasing the sensitivity of detection. On the contrary, it has been shown that when the PA difference between the molecule and water is small, as for formaldehyde for instance (PA(H 2 CO)0 711.0 kJ mol − 1 ) [36], involving a difference of 20 kJ mol −1 , the back-reaction of the protonated molecule with water occurs and reduces the sensitivity [37]. As indicated in "Quantum chemistry calculation of proton affinities and proton transfer reaction rate coefficients", PA(1) is close to 880 kJ mol −1 , while PA(2) and PA(3) are close to 900 kJ mol −1 .…”

From a Network of Computed Reaction Enthalpies to Atom‐Based Thermochemistry (NEAT)

“…It is often not possible to fulfill all these criteria simultaneously and thus some care should be exercised when selecting the best reaction. For example, when trying to determine the enthalpy of formation of formaldehyde it is advantageous [80] to use the reaction H 2 CO = H 2 + CO over either…”