Classical description in a quantum spirit of the prototype four-atom reaction OH + D2

Abstract

Classical mechanics is the only practical way to simulate internuclear motion in many complex systems that are important for biology, materials science, and technology. It is therefore important to test classical dynamics on simpler systems. The OH + H(2) or OH + D(2) system is the prototype four-body chemical reaction for fundamental studies of this nature, and high-resolution experiments have been reported by Davis and co-workers. Here we use those experiments to test state-resolved quasi-classical trajectory calculations in a quantum spirit, and find good agreement with experiment. Our simulations correctly predict that the newly formed oxygen-deuterium bond in the HOD product is preferentially excited to the vibrational state v = 2, and they yield a state-resolved product translational energy distribution. Of special interest is that the triple (angle-velocity) differential cross section shows the same state-resolved structure associated with the product vibrational states that were analyzed. This level of accuracy has previously been achieved only for triatomic systems, and these new simulations demonstrate that the quasi-classical method with quantum corrections may represent a reasonable alternative to quantum scattering approaches for the description of polyatomic reaction dynamics.

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

“…Quasi-classical trajectory (QCT) calculations on the benchmark polyatomic reaction OH + D 2 were recently performed [10] on the OC potential energy surface (OC-PES) [3] at the conditions of the experiment of Davis and co-workers [4]. The overall agreement was satisfying, but one of the three main vibrational states available was found to be significantly lower than its experimental measure [10].…”

“…Since the experiment was not carried out at J = 0, one could think that the total angular momentum is responsible for this discrepancy. However, previous QCT calculations on the same PES at total angular momentum different from zero [10] found a similar underestimation of the population of the (1, 1) state, ruling out the role of the total angular momentum in this discrepancy.…”

“…Recently we carried out QCT calculations on the Ochoa-Clary surface (OC-PES) [10], which was also used in the above mentioned AQS calculations [5]. So, this PES represents an excellent opportunity to test the validity of the QCT method, as compared with AQS and EQS calculations.…”

“…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].…”

“…HOD + D is a benchmark polyatomic bimolecular reaction [2][3][4][5][6][7][8][9][10][11]. It is the analogue of F + H 2 ?…”