Yr. Ou et al., AB-INITIO CALCULATION FOR POTENTIAL-ENERGY SURFACES RELEVANT TO THE MICROSCOPIC REACTION PATHWAYS FOR MG(3S3P(1)P(1))-2-]MGH((2)SIGMA(+))+H(H), The Journal of chemical physics, 108(4), 1998, pp. 1475-1484
Two ab initio methods have been employed to calculate the dynamical po
tential energy surfaces (PES's) for the excited (B-1(2) Or (1)A') and
the ground ((1)A(1) or (1)A') states in the Mg(3s3p(1)P(1),)-H-2 react
ion. The obtained PES's information reveals that the production of MgH
in the (2) Sigma(+) state, as Mg(P-1(1)) approaches H-2 in a bent con
figuration, involves a nonadiabatic transition. The MgH2 intermediate
around the surface crossing then elicits two distinct reaction pathway
s. In the first one, the bent intermediate, affected by a strong aniso
tropy of the interaction potential, decomposes via a Linear HMgH geome
try. The resulting MgH is anticipated to populate in the quantum state
s of rotational and vibrational excitation. In contrast, the second pa
thway produces MgH in the low rotational and vibrational states, as a
result of the intermediate decomposition along the stretching coordina
te of the Mg-H elongation. These two tracks may account for the previo
us experimental findings for the MgH distribution, which the impulsive
model has failed to comprehend. By far, different interpretations hav
e been proposed especially for the low-N MgH product. The supply of a
detailed PES's information in this work helps to clarify the ambiguity
. It is also conducive to an interpretation of the isotope and tempera
ture effects on the product rotational distribution. (C) 1998 American
Institute of Physics. [S0021-9606(98)00104-4].