Classical treatment of molecular collisions: striking improvement of the description of recoil energy distributions using Gaussian weighted trajectories

Abstract

The Gaussian weighting (GW) procedure, recently used in the classical treatment of molecular collisions, is a practical way of taking into account quantization of product vibrational actions. The goal of this brief communication is to show that the GW procedure may drastically improve the predictions of the recoil energy distribution between final fragments, an observable frequently measured in molecular beam experiments.

Quasi-classical statistico-dynamical description of polyatomic photo-dissociations: state-resolved distributions

“…Note, for example, the strong discrepancy of the ZPE-corrected curve which fails to reproduce any of them. Moreover, to achieve a similar agreement with the experiment in the case of the triatomic dissociation NCO −→ N + CO, the GM method had to be applied [9]. However, the divergence between the experimental and ZPE distributions has an additional important implication.…”

Classical versus quantum vibrational state distributions for the benchmark polyatomic reaction OH+D2: Checking the validity of the QCT method

“…To deal with vibrational quantization in the products within the QCT method, we used the GB procedure [17][18][19][20][21][22][23][24][25][26][27][28] which can be summarized as follows: Bohr's basic idea is that only the classical paths corresponding to integer actions of the final products should be permitted. This is also an idea to which the classical S matrix theory (CSMT) of Miller and Marcus leads [32][33][34][35][36][37][38].…”

“…When in the QCT calculations the standard binning (SB) procedure (which amounts to attribute the same statistical weight to each trajectory) was used, the experimental product vibrational state populations were not reproduced [6][7][8][9]. However, using the Gaussian binning (GB) procedure, which takes into account Bohr quantization principle for vibrational energies [17][18][19][20][21][22][23][24][25][26][27][28], made the expected product state spectrum appear, for the first time as far as polyatomic processes are concerned [10]. However, this method (QCT-GB) gives a population of the (1, 1) state of 3%, much lower than the experimental value, 11% [10].…”

Classical photodissociation dynamics with Bohr quantization

“…However, this procedure may lead to unrealistic predictions when a small number of quantum states are available to the products, as shown in the recent years. As previously stated, a possible alternative to the SB procedure is the GB one [14][15][16][17][18][19][20][21], where the delta-function constraining the action is replaced by the Gaussian function…”

“…In recent years, the Gaussian Binning (GB) procedure (see the next section) was frequently used to include Bohr quantization of product internal motions in QCT calculations, removing thereby to some extent the previous drawback [14][15][16][17][18][19][20][21]. However, this procedure is numerically inefficient for larger than four-atom systems.…”