AN AB-INITIO STUDY OF THE GROUND AND FIRST EXCITED-STATE OF HCN[--]HNC ISOMERIZATION AND A CALCULATION OF THE HNC A-]X FLUORESCENCE-SPECTRUM

We report ab initio calculations of the minima and transition states of the HCN --> HNC isomerization in the X(A') and A(A'')) electronic states, and the A-X transition moment in the neighborhood of the HNC isomer. The HNC(A) potential is fit to a fourth-order Simons-Parr-Finlan force field, and the nuclear coordinate dependence of the A-X transition moment is fit to a polynomial in displacement coordinates. The A-X fluorescence spectrum is calculated using a rigorously calculated wavefunction for the HNC(A), the fitted transition moment, and hundreds of previously calculated HCN/HNC(X) vibrational wavefunctions, which were obtained using a previous global ab initio potential.