Energies and Potential Surfaces of the Excited Electronic States of the Triazines

Principal Investigator

Gad Fischer

Chemistry

The Faculties

Triazines are six-membered rings with the number of adjacent nitrogens ranging from three in 1,2,3-triazine to one in s-triazine. Triazines are characterized by varying stabilities, differing symmetries and a gradation in aromaticities. Complementing experimental work on the electronic spectroscopy, ab initio molecular orbital calculations have been undertaken to determine the electronic state energies and vibrational frequencies.

Co-Investigators

Xiaolin Cao

Chemistry

The Faculties


Projects

u01 - VP, PC

What are the results to date and the future of the work?

Several different theoretical methods have been used to gain extensive and balanced theoretical descriptions of the excited states of the triazines. The theoretical results have been compared with experimental work. An analysis of the electronic spectrum of 1,2,3-triazine has been achieved, although to some extent the theoretical predictions at different levels of ab initio theory (CIS, CASSCF, and CASSCF/MRCI) are conflicting. Further work for 1,2,3-triazine requires characterization of the other near-resonance singlet A2 state. The calculations are complete for 1,2,4-triazine but experimental results for comparison are lacking. Problems have been encountered with the s-triazine calculations because of the high symmetry, and these still need to be resolved. Calculations have also been carried out on the characterization of the ground state of benzotriazole, a nitrogen heterocycle with three adjacent nitrogens.

What computational techniques are used?

Both the GAUSSIAN and MOLPRO packages have been used. The CIS/6-31G* calculations were performed on GAUSSIAN, and most of the CASSCF calculations with MOLPRO. The CIS computations give excited state optimized geometries and potential surfaces, while the CASSCF can give optimized geometries, and in some cases vibrational frequencies.

Publications

G. Fischer, X.Cao and R. L. Purchase, FT-IR spectrum of the 2H-tautomer of benzotriazole in a supersonic jet., Chem. Phys. Letts. 262, 689-698 (1996).

G. Fischer, A.U. Nwankwoala and D.M. Smith, The electronic spectroscopy of 1,2,3-triazine, Submitted to Chem. Phys.