CONFIGURATION-INTERACTION CALCULATIONS ON THE X 1-SIGMA+ GROUND-STATE AND LOW-LYING A 1-PI AND 1-DELTA EXCITED-STATES OF THE PN MOLECULE .2. POTENTIAL-ENERGY CURVES OF THE A 1-PI AND 1-DELTA EXCITED-STATES OF PN AND SPECTROSCOPIC PROPERTIES

CI calculations have been performed on the A 1PI and 1DELTA states of PN in the vicinity of their respective equilibrium geometries, yielding spectroscopic constants (r(e), k(e), omega(e), omega(e)x(e), etc) in good agreement with the available experimental data. The 1DELTA state, which is unknown experimentally, is predicted to lie less than 500 cm-1 above the 1PI state and 40 345 cm-1 above the 1SIGMA+ ground state. Theoretical vibrational bands for the A 1PI --> X 1SIGMA+ transition were computed, along with the corresponding Franck-Condon factors. The calculated vibrational transitions agree quite well with the observed values while the Franck-Condon factors compare favourably with those calculated semiempirically from observed vibrational transition probabilities. The sequence of absolute radiative intensities for the rovibrational (j' = 4) bands \upsilon', upsilon'')], i.e. \(0,0)]\(1,0)]\(2,1)]\(3,2)]1\(4,3)], cannot be confirmed experimentally because of the perturbation of nearby states on low-lying 1PI vibrational states (upsilon' = 0-4). Spontaneous radiative and non-radiative lifetimes derived according to two decay mechanisms-a cascade (A 1PI state being 'isolated') mechanism and an electric dipolar transition mechanism-show that the latter mode of decay is several orders of magnitude larger. The single experimentally known lifetime value, i.e. for upsilon' = 0, issued from this decay mode agrees reasonably well with the calculated value. For the 1DELTA --> A 1PI transition, the electric dipolar decay is only slightly favoured with respect to the cascade mode. The lifetimes computed for both decay modes are found to be close to those in the valence isoelectronic CO molecule. Other miscellaneous observables, which to date have not been determined experimentally for these excited states, including pure rotational, pure vibrational and rovibrational transitions, selected one-electron properties and average values of the electric dipole moment over the first few vibrational levels (upsilon = 0-5) are likewise reported.