Spin–orbit effects in the decomposition reaction N3H(X̃1A′)→N2(X1Σ+g)+NH(X3σ−, a1Δ)

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Abstract
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 N3H(X̃1A’)→NH(X3Σ−)+N2(1Σ+g) 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’(3A‘) ≡i{Ψ[1 3A‘(1)] −Ψ[1 3A‘(−1)]}/(2)1/2 were determined in the asymptotic region corresponding to N2+NH, at the (experimental) equilibrium geometry of N3H(X̃ 1A’) and in the vicinity of the (approximate) minimum energy singlet–triplet crossing. At the approximate minimum energy crossing we find hsoz ≡〈Ψ1a’(1A’)‖Hso‖ Ψ1a’(3A‘)〉 ≊39 cm−1 ≫hsoy ≡〈Ψ1a’(1A’)‖Hso‖ Ψ2a’(3A‘)〉 ≊0.45 cm−1. The matrix elements hsoz,hsoy 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.