The vibrationally adiabatic distorted wave method for direct chemical reactions: Application to X+F2(v = 0, j = 0)→XF(v′, j′, m j′)+F(X = Mu, H, D, T)

Abstract

The computational feasibility of the vibrationally adiabatic distorted wave (VADW) method is examined for the prediction of vibration–rotation product distributions of atom–diatomic molecule chemical reactions when there are a large number of open product states present. Application is made to the chemical laser reactions X+F2(v = 0, j = 0)→XF(v′, j′, mj′)+F (X = Mu, H, D, T) in three dimensions (3D). Over 1000 product vibration–rotation TF states are open in the T+F2 reaction. The best extended LEPS no. II potential energy surface of Jonathan et al. is used. The relative vibrational product distribution P(v′) for the H+F2 reaction at a translational energy of 0.106 eV peaks at v′ = 6. It agrees well with thermal experimental measurements and with previous 3D quasiclassical trajectory, accurate 1D quantum, and 1D→3D information theoretic calculations. The P(v′) for the Mu, D, and T reactions are found to peak at v′ = 1, 9, and 12, respectively, which is in good agreement with the results of the 1D→3D method. The average available energy present in product vibration is found to increase with increasing mass of X, in agreement with the 1D→3D results and the light atom anomaly concept. The relative rotational product distribution for H+F2 agrees well with thermal experimental results, with very low rotational excitation. The average available energy present in product rotation is very low for all four reactions and decreases slightly as the mass of X increases. The product differential cross sections for the H, D, and T reactions are distributed in both the forward and backward directions, while the Mu reaction is purely backward scattered. In every case the cross section for reaction into the state v′, j′,‖mj′‖ is greater than that for reaction into v′, j′,‖mj′‖+1. The VADW technique is computationally inexpensive; only 20 min of CDC 7600 computer time are required to compute the full vibration–rotation product distributions for the H+F2 reaction at one energy.