Directab initiomolecular dynamics study of F atom reaction with methane

Abstract

The dynamics of the F þ CH 4 ! HF þ CH 3 and F þ CD 4 ! DF þ CD 3 reactions have been investigated using classical trajectory calculations at the MP2/cc-pvdz level of theory. The trajectories were calculated directly from electronic structure computations, and a Hessian based method with updating was used to integrate the trajectories. Using this method, product rovibrational populations and internal energy distributions were obtained for the F þ CH 4 and F þ CD 4 reactions. The theoretical results were compared with the available experimental data and previous calculations results. The state distributions of the reaction F þ CH 4 in these calculations are in reasonable agreement with the experimental results, which indicates that the experimental behavior of the reaction could be well reproduced by the direct classical trajectory calculations at MP2/cc-pvdz level. As such, the product rovibrational populations and internal energy distributions for the reaction F þ CD 4 were predicted. The same degree of agreement between theory and experiment as the F þ CH 4 reaction is expected.

On the signal depletion induced by stretching excitation of methane in the reaction with the F atom

“…These notions are confirmed by ab initio calculations. 4,5,[50][51][52][53][54][55] One of the theoretical studies further indicated two low intermolecular bending frequencies (40 cm À1 and 117 cm À1 ) at the reaction saddle point, 4,5 implying a loose-bend transition state. In addition, two van der Waals (vdW) complexes of C 3v symmetry are calculated in the reactant channel.…”

A Quasiclassical Study of the F(2P) + CHD3 (ν1 = 0,1) Reactive System on an Accurate Potential Energy Surface

“…A typical example is the investigation of the reaction between fluorine atoms and different isotopologues of methane. The last 15 years have witnessed the realization of detailed experiments on such systems, which uncovered several interesting dynamical features. − However, among those experimental results, only the photodetachment spectra of FCH 4 – and FCD 4 – (refs and ) could be contrasted against rigorous first-principle-based computations. − In other cases, quasiclassical trajectories (QCT) − or reduced dimensionality calculations − were employed to reproduce and interpret the experiments.…”

Imaging the Effects of Bend-Excitation in the F + CD4(vb=0,1) → DF(v) + CD3(v2=1,2) Reactions

“…We recently reported an experimental investigation on the effects of reactant’s bending excitations in the F + CD 4 → DF + CD 3 reaction . The reaction of F + CD 4 is highly exothermic (Δ H rx = −31.13 kcal mol –1 ) and very fast ( k = 6.7 × 10 –11 cm 3 molecule –1 s –1 at 298 K) , with an early barrier. − To scrutinize the bend-excited reactivity, the experiment was performed under the crossed-beam conditions, using a time-sliced velocity-imaging technique to probe the predominant ground-state methyl radical products, CD 3 (0 0 ,low N -states) . Two major findings were reported.…”