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Manuscript Title: RT3: A Windows Program for the Renner-Teller Analysis of 2Π States of Triatomic Molecules
Authors: Sheng-Gui He, Dennis J. Clouthier
Program title: RT3
Catalogue identifier: AEAL_v1_0
Distribution format: tar.gz
Journal reference: Comput. Phys. Commun. 178(2008)676
Programming language: Visual Basic 6.0, Fortran 90.
Operating system: Windows 98, Windows XP, Windows Vista, UNIX.
Keywords: Renner-Teller, Spectroscopy, Doublet Pi States.
PACS: 33.20.Wr, 33.20.Kf, 33.20.Lg.
Classification: 16.2.

Nature of problem:
The vibronic levels of triatomic molecules in 2Π states are complicated by spin-orbit and vibrational-orbital angular momentum coupling (Renner-Teller) effects that make them difficult to assign and analyze. The RT3 program, available in Windows and Fortran versions, can be used to calculate the vibronic energy levels of such systems and fit experimental data to a Hamiltonian that includes Renner-Teller, spin-orbit, vibrational anharmonicity, Fermi resonance and Sears resonance effects.

Solution method:
The RT3 program solves for the Renner-Teller levels of a 2Π state by diagonalizing large truncated hamiltonian matrices whose elements are generated in a harmonic oscillator basis set. Given an initial input set of constants, the resulting energy levels can be used to least squares fit or predict vibronic term values (relative to the lowest energy level), combination differences between vibronic levels within a electronic state, and transitions between the vibronic levels of two different 2Π states.

Running time:
6.0 s to run the Transitions.ir3 example file on an Intel Pentium 4 2GHz CPU with the Windows XP operating system.