Four-center reactions: A quantal model for H4

Abstract

Analytical potential energy surface for the CH4+ClCH3+ClH reaction: Application of the variational transition state theory and analysis of the kinetic isotope effects J. Chem. Phys. 105, 3517 (1996) We develop a quantal model for studying four-center reactions, A 2 ϩB 2 →2AB, and collision induced dissociation A 2 ϩB 2 →AϩB 2 ϩA. The method involves using hyperspherical coordinates to describe vibrations of the A 2 and B 2 bonds and a global vibration and rotation of the exchange products. Application to the H 4 system is presented, using a realistic potential energy surface. The reaction goes through a four-center linear transition state located just above the dissociation threshold. In the energy range studied ͑5-5.5 eV͒, collision induced dissociation competes with the four-center reaction and is the dominant process. It is found that vibrational energy, originally deposited in one of the diatomic partners, is much more efficient than translational energy in promoting reaction. Vibrational and rotational final distributions show that the products are internally hot. This simple quantal model, yet very demanding computationally, illustrates in detail many features of the H 4 dynamics above the dissociation threshold, and could serve to study other four center reactions with trapezoidal or linear transition states.

Fully converged integral cross sections of collision induced dissociation, four-center, and single exchange reactions, and accuracy of the centrifugal sudden approximation in H2 + D2 reaction

“…[30][31][32][33][34][35][36][37][38] and reduced dimensional quantum mechanical (QM) methods. 29,[39][40][41][42][43][44] Lu et al 45 carried out the first accurate full-dimensional QM calculations of the H 2 + H 2 reaction using the time-dependent wave packet method. In their study, initial state selected total reaction probabilities for the three competitive processes were reported with total angular momentum J = 0, and the effect of reagent vibration on reactions was examined on the ASP PES.…”

“…In contrast to three-center reactions where only one bond is broken and formed during the reaction process, 4C reactions involve simultaneous cleavage and formation of two bonds, and they usually present very high barriers, comparable to or higher than a covalent bond energy. 29 The coexistence of several processes and the higher energy required to surmount the barrier pose a challenge to the exact full-dimensional quantum studies of the reaction dynamics. Therefore, most theoretical dynamics studies have been performed using reduced dimensional or fulldimensional classical or quasi-classical trajectories (QCT) (Refs.…”

Wave packet calculations for H2+H2collisions: isotopic substitution effects

“…To do this, we have considered, as 'reference' processes, the collision of H 2 ðv 1 ¼ 10À14Þ þ H 2 ðv 2 ¼ 0À2Þ, previously reported in [11]. Note that all initial states involve one reactant vibrationally excited and the other one vibrationally cold, since we have found [9] that these states are the most effective ones both for CID and for reaction. On the one hand, we analyse the substitution of collider H 2 ðv 2 ¼ 0À2Þ by D 2 in the same vibrational states, and, on the other hand, the substitution of target H 2 ðv 1 Þ by D 2 in a vibrational state such that the vibrational energy is most similar.…”

“…The reduced dimensionality model was that of [9], where the atoms are restricted to be within a trapezoidal geometry, and 4C and CID probabilities from selected reagent vibrational states can be obtained (see figure 1). It should be noted that accurate fulldimensional quantum mechanical calculations are nowadays unfeasible since, at the high energies considered, many states are populated and dense grids or large basis sets are needed in the calculations.…”

Wave packet calculations for H2(v1=10–14)+H2(v2=0–2): Reaction and dissociation mechanisms

“…6 Several dynamical studies have been subsequently published, using full 1,10-12 or reduced 11,13 dimensionality quasiclassical trajectory ͑QCT͒ calculations as well as reduced dimensionality quantummechanical calculations. 14,15 An account of previous dynamical studies is given in Ref. 14.…”