Classical trajectory studies of the molecular dissociation dynamics of formaldehyde: H2CO→H2+CO

Abstract

Classical trajectory calculations have been carried out to simulate the unimolecular decomposition of formaldehyde in the ground electronic state (Se). Global potential-energy surfaces were constructed using the empirical valence-bond (EVB) approach. Two sets of ab initio input were used to characterize two different EVB potential-energy surfaces, and trajectory calculations using one of these gives excellent agreement with experimental data for the product-state distributions of H2 and CO. The trajectory study of vector correlations with prompt dissociation of the parent molecule provides understanding of the dissociation dynamics in the molecular frame. From comparison with some of the experimental results and information from a few ab initio calculations, some improvements for the current potential surfaces are suggested.

Confinement effects on chemical reactions—Toward an integrated rational catalyst design

“…CO + H 2 to proceed in the gas phase with an energy barrier of 80.3 kcal/mol, in good agreement with the experimental value of 79.2 AE 0.8 kcal/mol [51,52] and other theoretical results [53][54][55][56][57][58][59][60][61][62][63][64]. The geometries of the reactants, products, and transition state are also in good agreement with other theoretical calculations.…”

Optimizing the Performance of the Multiconfiguration Molecular Mechanics Method

“…The diagonal elements may be interpreted as the energies of individual valence bond configurations, as in semiempirical valence bond theory, 7−23 and therefore the off-diagonal element (diabatic coupling) may be interpreted as a resonance integral. The resonance integral and its Taylor's series expansion 24,25 at a geometry q, are obtained from electronic structure calculations of the Born-Oppenheimer potential energy, and in MCMM these Taylor's series have been joined into a global potential energy surface (PES) by means of multidimensional Shepard interpolation 27,28 in internal coordinates. 1 (An alternative recently proposed is to fit V 12 by a polynomial times a spherical Gaussian.…”

Empirical valence bond models for reactive potential energy surfaces. II. Intramolecular proton transfer in pyridone and the Claisen reaction of allyl vinyl ether

“…The optimized alpha values are given in table 4. Although the potential energy profile appears simple enough, V 12 (q) 2 is considerably more complex (see figures [7][8][9]. For the pyridone tautomerism, V 12 (q) 2 is essentially a 'onehumped camel', but in the Claisen reaction V 12 (q) 2 is a 'multi-humped camel' and therefore more difficult to reproduce.…”

“…Unfortunately, the Chang-Miller approach runs into some difficulties when C has one or more negative eigenvalues [4,7,8].…”

“…To facilitate the solution of the fitting parameter linear equations, the s-type Gaussians in equation (8) are replaced by…”