Quasiclassical Trajectory Study on the Role of CH-Stretching Vibrational Excitation in the F(²P) + CHD₃(v₁=0,1) Reactions

Abstract

To analyze the role of CH-stretching vibrational excitation on the reactivity and dynamics of the F((2)P) + CHD3(v1=0,1) reactions, quasiclassical trajectory calculations using a full-dimensional analytical potential energy surface at different collision energies were performed. The extra energy of the CH excitation had almost no effect on the reactivity for the DF + CHD2 channel, although it increased the reactivity for the HF + CD3 channel, with the net effect being that CH excitation barely modified overall reactivity. In addition, the DF/HF branching ratio was not far from the statistical value for the ground-state reaction, whereas CH excitation decreased this ratio. These results, intimately related to the topology of the entrance channel, agree with recent theoretical results obtained using different surfaces (although some differences even persist among them) but strongly contradict recent experiments. This controversy will doubtless guarantee more accurate experiments and theoretical calculations in the future. However, properties related to the exit channel show reasonable theoretical/experimental agreement. Thus, the extra energy of CH excitation is mainly channelled into the HF and DF products for the HF + CD3 and DF + CHD 2 channels, respectively, and the product scattering distributions are forward in both channels, where CH excitation has almost no effect on them.

From Reactive Rainbow to Dynamic Resonance Well

“…The above experimental value is significantly larger than the theoretically calculated F···CH 4 vdW well of 0.48 kcal mol –1 (the exit channel FH···CH 3 complex on the new PES is about 1.4 kcal mol –1 deep) . The latter agrees very well with earlier results of 0.13–0.46 kcal mol –1 . − Based on that newly developed PES and a reduced 8D model under C 3 v symmetry, − the vibrationally adiabatic potentials for the CH 3 (0 0 ) + DF­( v ) channels are calculated (Figure S1) and predicted an adiabatic well depth of about 4.4 kcal mol –1 for DF­( v = 4). This value compares favorably with another theoretically predicted well of 3.0 kcal mol –1 for the CH 3 (0 0 )·HF­( v = 3) resonant complex .…”

Control of chemical reactivity by transition-state and beyond

“…However, more recent theoretical investigations, also by QCT but on different PESs in the entrance valley, suggested no inhibitory effect by CHD 3 ( v 1 = 1). 111 , 112 The source of the theory-experiment discrepancy is unclear at present. On the experimental side, it could arise from some other excited methyl products, which are inaccessible to the current REMPI detection method and yet with much higher abundances than those states being probed thus far.…”

Rate constant calculations of the GeH4 + OH/OD → GeH3 + H2O/HOD reactions using an ab initio based full-dimensional potential energy surface

“…A similar problem was found in the study of the F( 2 P) + CH 4 reaction and its isotopic variants, which also presents a high exothermicity, À30.0 kcal mol À1 , and low barrier height, o1 kcal mol À1 . Three full-dimensional PESs were developed for this system by different groups with different strategies, [18][19][20][21] and it was found that small topology changes in the entrance channel can modify the dynamics (excitation function, vibrational distribution of the products, or the scattering distribution).…”