SPIN ORBIT EFFECTS IN THE DECOMPOSITION REACTION N3H(X1A')-]N2(X1-SIGMA-G+)+NH(X3-SIGMA, A1-DELTA)

Using a flexible basis of better than double zeta-polarization quality and configuration interaction (CI) expansions of approximately 200 000 terms the electronic structure aspects of the spin-forbidden decomposition reaction N 3H(X̃ 1A′)→NH(X 3Σ -) + N2(1Σg+) were studied. The spin-orbit interaction (Hso) was treated within the Breit-Pauli approximation including both the microscopic spin-orbit and spin-other-orbit contributions. Matrix elements of Hso between the lowest singlet state ψ1a′ (1A′) ≡ψ[1 1A′ (0)] and the components of the lowest triplet state ψ1a′, (3A″)≡iψ[1 3A′ (0)], ψ2a′.(3 A″) ≡i{ψ[1 3A″ (1)] - ψ [1 3A″ ( -1 )]}/√2 were determined in the asymptotic region corresponding to N 2 + NH, at the (experimental) equilibrium geometry of N 3H(X̃ 1A′) and in the vicinity of the (approximate) minimum energy singlet-triplet crossing. At the approximate minimum energy crossing we find hzso ≡ 〈ψ1a′ (1 A′)\Hso|ψ 1a′ (3A″)〉 ≈ 39 cm-1 ≪ hyso≡ 〈ψ1a′(1 A′)\Hso| ψ2a′ (3 A″)〉 ≈ 0.45 cm-1. The matrix elements hzso ,h yso are interpreted in terms of a single configuration model and are compared with analogous quantities in the isolated NH molecule. A qualitative discussion of the decomposition reaction using a Landau-Zener approach is given. © 1990 American Institute of Physics.