Spectroscopy of diatomic molecules

The problem: exploration of outer space

Diatomic molecules containing transition metals have received a lot of attention lately. This interest stems from their occurrence in Astrophysics. The main sources of information for astrophysicists are the microwave or millimeter wave spectra of stars and galaxies. Such spectra are in general exceedingly complicated, due to several perturbations such as spin-orbit coupling.

Reference to comparison is hardly available, and this turns Theoretical Chemistry a valuable aid for the interested researchers. On the other hand, the development of personal computers has led to the readily available computational power that was previously at hand only for University researchers. Nowadays anyone can perform such calculations at home.

Previous Work

Until the late seventies the most reliable source of data was the monumental compilation done by Herzberg. At that point the computational implementation of ab initio correlated wavefunctions became an accessible tool to a large portion of the academic community. In those days Bauschlicher and others built extended basis sets for the transition metal (TM) series, and explored the addition of polarization and diffuse functions. The eighties and nineties saw a number of applications of MCSCF calculations, mainly on TM oxides. The group of the late Bjorn Roos developed implementations of CISD calculations based on a complete active space (CAS), and extended the method to include perturbational corrections in the CASPT2 method. This is the current state-of-the-art for variational methods.

What we have done

We have recently studied low lying states of iron mononitride (FeN). Our reference wavefunction was built at CAS-SCF level using a aug-cc-pVTZ basis set.


These optimized MOs were used in a second-order CI. The variational space reached a couple of million configuration state functions (CSFs). We have obtained an extensive list of spectroscopic constants for several low lying states of FeN.

We have also examined other diatomic molecules such as MnN, VH, NiN and NCl.

Current perspectives – collaboration with the ETER group at CTA-ITA

We are now examining a number of different systems of tecnological interest at the ETER group at the Air Force Academy at São José dos Campos, SP.


[1] Anthony J Merer, Spectroscopy of diatomic 3d Oxides, Ann. Rev. Phys. Chem. 40, 407-438 (1998).
[2] James F. Harrison, Chemical Reviews 100(2), 679-716 (2000).

[3] M.H. Oliveira, H.P. Martins Filho and J.D. Da Motta Neto, Int. J. Quantum Chem. 111(7-8), 1453-1457 (2010). First published online June 28th, 2010. DOI. 10.1002/qua.22685