Nonadiabatic quantum dynamics of the charge transfer reaction H+ + NO(X2Π) → H + NO+(X1Σ+)

Abstract

Nonadiabatic quantum dynamics of the charge transfer (CT) reaction H⁺ + NO(X²Π) → H + NO⁺(X¹Σ⁺) is investigated on a new diabatic potential energy matrix (PEM) including the 1²A′ and 2²A′ states of HNO⁺/HON⁺ at the multireference configuration interaction level with Davidson correction using a large basis set. The diabatization of the two coupled states was achieved by the adiabatic-to-diabatic transformation with a mixing angle and the final diabatic PEM was obtained by fitting each matrix element separately using a three-dimensional cubic spline interpolation including more than 22 000 ab initio points. The reaction was found to be dominated by the resonances supported by the double well associated with HNO⁺ and HON⁺ species, manifested by the oscillatory structures in the reaction probabilities and product rotational distributions. The product vibrational states were highly excited due to the large exothermicity of the reaction. Consistent with the complex-forming mechanism, the differential cross sections (DCSs) were found to be dominated by the forward and backward scatterings. A clear forward bias in the vibrational state resolved DCSs suggests that the non-statistical behavior of the reaction mainly comes from the low vibrational states of the product. In addition, the rate constants of the reaction in the temperature range from 50 to 500 K were computed for the first time and found to be in fairly good agreement with the available experimental results at 300 K. In particular, compared to other reactions involving neutral species in this system including N, O, and H atoms, such a CT reaction was found to be much more reactive, which has rate constants more than thirty times larger.