Revisiting the F + HCl → HF + Cl reaction using a multireference coupled-cluster method

Abstract

We have constructed a new potential energy surface for the title reaction, based on the internally contracted multireference coupled-cluster method. The calculated barrier height is 1.59 ± 0.08 kcal mol. This value is much lower than that obtained in previous ab initio calculations and it is close to the experimentally suggested value. Other features of the [F,H,Cl] system are also analysed, such as van der Waals minima and conical intersections. The rate constant and the vibrational and rotational distributions of the products were calculated using a fully converged time independent quantum mechanical approach. The calculated rate constant agrees well with the experimental values. Qualitative agreement for the vibrational distribution is obtained and it is shown that it is strongly influenced by the initial rotational state distribution.

Quantum tunneling during interstellar surface-catalyzed formation of water: the reaction H + H2O2 → H2O + OH

“…The icMRCCSD(T) method translates the accuracy of CCSD(T) to multireference cases and has been successfully applied to predicting barriers of reactions. 86 An estimate of the multireference effects can be obtained from the results of icMRCCSD(T) and UCCSD(T) calculations using the cc-pVTZ basis. The computations indicate, that multireference effects only slightly lower the activation energy (–2.8 kJ mol –1 for (R1) and –1.3 kJ mol –1 for (R2)).…”

The Molpro quantum chemistry package

“…Using this interface, a number of demonstrative applications have been carried out in the past, like a highly accurate reactive potential energy surface for [F,H,Cl] 142 or a set of benchmark computations for diatomic transition metal compounds. 143 In order to address larger systems, an embedding scheme has been developed 144 that was inspired by the 'region' approximation originally developed for LCCSD(T).…”

Machine Learning Quantum Reaction Rate Constants

“…In panels c and d of Figure , we show results for the reaction of F with HCl. The MEP was fitted to that of ref . For panel c, the value of the activation energy, 7.21 kcal/mol, was obtained from the fit to an Eckart barrier.…”

“…From the bottom graph we note that the DNN is able of predicting accurately. In panel d, the value of the activation energy for the same F + HCl reaction was taken from a higher level multireference coupled-cluster study and is outside of the range of values seen when the network was training. This extrapolation leads to a larger error in prediction; nonetheless the DNN is accurate in predicting the rate at low temperatures.…”

“…Lower plot,panel c: comparison of the exact log­( k Q ) for the reaction (blue with circles) with the DNN prediction (red with triangles) and transition state theory (black line) when the activation energy is taken from the fit. Lower plot, panel d: same as the lower plot of panel c, but with a lower more accurate activation energy …”