Potential energy curves for the dissociation of the Rydberg NH4 radical into (NH2+H2)

Potential energy curves of the ground and excited states for the dissociation of the Rydberg NH4 radical into (NH2 + H-2) have been calculated using ab initio Hartree-Fock and Singly and doubly excited configuration interaction methods with a large basis set including Rydberg basis functions. The ground potential curve ((2)A(1)) of the (NH4+)(e(-))(3s) radical adiabatically correlates to the [NH2*((A) over tilde (2)A(1)) + H-2((X) over tilde (1)Sigma(g)(+))] asymptote, while the first excited state (T-2(2)) of (NH4+)(e(-))(3p) correlates to [NH2((X) over tilde B-2(1)) + H-2((X) over tilde (1)Sigma(g)(+))]. Two diabatic valence curves emerging from the [NH2*((A) over tilde (2)A(1)) + H-2((X) over tilde (1)Sigma(g)(+))] and [NH2((X) over tilde B-2(1)) + H-2((X) over tilde (1)Sigma(g)(+))] asymptotes are repulsively represented, while two diabatic curves from [NH2+((A) over tilde (1)A(1)) + H-2(-)((X) over tilde (2)Sigma(u)(+))] and [NH2+((X) over tilde B-3(1)) + H-2(-)((X) over tilde(2) Sigma(u)(+))] are attractively represented. At shorter than R-(NH) similar or equal to 2.0 Angstrom, the avoided curve crossings between the dissociative diabatic states of the [(NH4+)(e(-))(Rydberg)] radical and the repulsive diabatic states emerging from the antibonding interactions of the [NH2 + H-2((X) over tilde (1)Sigma(g)(+))] asymptote are found mainly. While, at larger than R-(NH) similar or equal to 2.0 Angstrom, the avoided curve crossings between the repulsive diabatic states emerging from H2 and the Rydberg states of NH2 and the attractive diabatic states from [NH2+((A) over tilde (1)A(1)) + H-2(-)((X) over tilde (2)Sigma(u)(+))] and [NH2+((X) over tilde B-3(1)) + H-2((X) over tilde (2)Sigma(u)(+))] are found. (C) 1998 American Institute of Physics. [S0021-9606(98)00146-9].