Dynamical importance of van der Waals saddle and excited potential surface in C(1D)+D2 complex-forming reaction

Abstract

Encouraged by recent advances in revealing significant effects of van der Waals wells on reaction dynamics, many people assume that van der Waals wells are inevitable in chemical reactions. Here we find that the weak long-range forces cause van der Waals saddles in the prototypical C(1D)+D2 complex-forming reaction that have very different dynamical effects from van der Waals wells at low collision energies. Accurate quantum dynamics calculations on our highly accurate ab initio potential energy surfaces with van der Waals saddles yield cross-sections in close agreement with crossed-beam experiments, whereas the same calculations on an earlier surface with van der Waals wells produce much smaller cross-sections at low energies. Further trajectory calculations reveal that the van der Waals saddle leads to a torsion then sideways insertion reaction mechanism, whereas the well suppresses reactivity. Quantum diffraction oscillations and sharp resonances are also predicted based on our ground- and excited-state potential energy surfaces.

The dynamics of the C(1D)+H2/D2/HD reactions at low temperature

“…Previous investigations suggest that the overall dynamics of the reaction is governed by a complex-forming mechanism Thus, the preference for the formation of CH in its ground vibrational state, the inversion of the corresponding rotational distributions of CH(v = 0, j ) and the predominantly forwardbackward symmetry of the differential cross sections (DCSs) reported in the study by Shen et al [26] of the C( 1 D)+H 2 reaction seem to correspond to such dynamics. This symme-try around the sideways (θ ∼ 90 • ) direction which leads to almost identical peaks along the forward (θ ∼ 0 • ) and backward (θ ∼ 180 • ) scattering directions was also observed in a similar study for the C( 1 D)+D 2 reaction [25]. One of the conclusive tests to establish the importance of the complexforming pathway in atom-diatom reactions is the application of statistically-based approximative approaches which assume the formation of an intermediate species between reactants and products.…”

“…Some of these features are absent in previous PESs such as the BHL surface from Ref. [24] and its corrected form, the RKHS surface [3], and subtle differences in dynamical effects at low collision energies can be noticed [25]. The ZMB-a PES has been employed in theoretical studies of the C( 1 D)+H 2 reaction [26] and the C( 1 D)+D 2 [25] and C( 1 D)+HD [27,28] isotopic variants.…”

“…[24] and its corrected form, the RKHS surface [3], and subtle differences in dynamical effects at low collision energies can be noticed [25]. The ZMB-a PES has been employed in theoretical studies of the C( 1 D)+H 2 reaction [26] and the C( 1 D)+D 2 [25] and C( 1 D)+HD [27,28] isotopic variants. On the experimental side, rate coefficients at low temperatures (50-300 K) have been recently obtained by means of supersonic flow reactor investigations for the collision of a carbon atom both with H 2 [29] and D 2 [30].…”

“…We have also performed EQM calculations with the RWP method of Ref. [25] to complete the investigation on the C( 1 D)+D 2 reaction calculating ICS at lower energies, rotational and differential cross sections.…”

Quantum reaction dynamics of C(1D) + HD → CH(CD) + D(H) on the ground state potential energy surface

“…Besides, the calculated vibrational energy levels are also in better agreement with experiment than those computed on the BHL potential. QCT and QM studies for the reaction of C + H 2 (D 2 ) have been performed on this potential and obtained interesting results. Thus, to obtain more insight into the title reaction, it is desirable to investigate the quantum dynamics on this new constructed PES.…”