Accurate ab initio potential for the Na+...I* complex

Area of Science:

• Physical Chemistry
• Computational Chemistry
• Quantum Chemistry

Background:

• Understanding molecular interactions is crucial for predicting chemical behavior.
• Accurate potential energy curves are essential for describing molecular dynamics and spectroscopy.

Purpose of the Study:

• To compute accurate potential energy curves for the sodium cation-iodine atom complex.
• To investigate the electronic states and spin-orbit coupling effects on the complex.
• To provide parameters for model potentials and aid in spectroscopic simulations.

Main Methods:

• High-level ab initio calculations, including multireference configuration interaction and coupled clusters methods.
• Use of correlation-consistent basis sets and complete basis set (CBS) extrapolations.
• Inclusion of spin-orbit coupling effects through ab initio and semiempirical approaches.

Main Results:

• Potential curves for the 2pi and 2sigma electronic states exhibit distinct characters, with the 2pi state being bound and the 2sigma state unbound.
• Spin-orbit coupling primarily affects the omega = 12 states, resulting in mixed 2sigma and 2pi characters and reduced binding energies.
• The final CBS-extrapolated binding energy for the Na+...I* complex, corrected for zero-point vibrational energy, is 10.2 kcal/mol.

Conclusions:

• The anisotropic interaction of iodine's quadrupole moment with the sodium cation dictates the binding characteristics of the electronic states.
• Spin-orbit coupling significantly influences the electronic structure and energetics of the Na+...I* complex.
• The computed parameters and model potentials are valuable for simulating NaI photodissociation femtosecond spectroscopy.