Analytical Potential Energy Function for the Ground State X^{1} Sigma^+ of LaCl

摘要

The equilibrium geometry, harmonic frequency and dissociation energy oflanthanum monochloride have been calculated at B3LYP, MP2, QCISD(T) levels withenergy-consistent relativistic effective core potentials. The possibleelectronic state and reasonable dissociation limit for the ground state aredetermined based on atomic and molecular reaction statics. Potential energycurve scans for the ground state X^{1} Sigma^+ have been carried out with B3LYPand QCISD(T) methods due to their better performance in bond energycalculations. We find the potential energy calculated with QCISD(T) method isabout 0.5 eV larger than dissociation energy when the diatomic distance is aslarge as 0.8 nm. The problem that single-reference ab initio methods don't meetdissociation limit during calculations of lanthanide heavy-metal elements isanalyzed. We propose the calculation scheme to derive analytical Murrell-Sorbiepotential energy function and Dunham expansion at equilibrium position.Spectroscopic constants got by standard Dunham treatment are in good agreementwith results of rotational analyses on spectroscopic experiments. Theanalytical function is of much realistic importance since it is possible to beapplied to predict fine transitional structure and study reaction dynamicprocess.