Coupled abinitio potential energy surfaces for the reaction Cl(2P)+HCl→ClH+Cl(2P)

Abstract

We have constructed the 1²A′, 2²A′ and 1²A″ potential energy surfaces for the Cl(²P)+HCl→ClH+Cl(²P) reaction, together with the non-adiabatic coupling surface between the 1²A′ and 2²A′ states. All our calculations used the MOLPRO quantum chemistry package, with Dunning's correlation consistent augmented valence triple zeta 1-electron basis set. The 1²A′ and 1²A″ energies are calculated at the restricted open shell coupled cluster singles doubles with perturbative triples (RCCSD-T) level, whilst the 2²A′–1²A′ energy difference and the non-adiabatic coupling are calculated via the multireference configuration interaction (MRCI) technique. The non-adiabatic coupling is evaluated from transition matrix elements of the angular momentum operator, namely 〈1²A″∣L_x∣1²A′〉 and 〈1²A″∣L_x∣2²A′〉. The surfaces in a diabatic representation are fitted to rotated-Morse cubic-spline functions. The empirical long-range potentials of Dubernet and Hutson (J. Phys. Chem., 1994, 98, 5844), together with empirical short range potentials, are then combined with the fitted abinitio surfaces to produce a set of global potential energy surfaces. Convergence tests show that the height of the barrier at C_2v geometries is 0.4361 eV for the 1²B₁ state, and occurs at a ClHCl bond angle of 137°. The collinear barrier heights are 0.4939 eV on the ²Σ_u⁺ surface and 0.9416 eV on the ²Π_g surface.