RT3: A Windows program for the Renner–Teller analysis of image states of triatomic molecules Original Research Article

In this work we present Windows and Fortran programs which can be used for the Renner–Teller analysis of the vibronic levels of image states of linear, triatomic molecules. The programs can do least squares fitting of term values relative to the lowest energy level within a single image state, of combination differences between vibronic levels within a single image state or of transitions between the levels of two different image states. The algorithm allows for the inclusion of Renner–Teller, spin–orbit, vibrational anharmonicity, Fermi resonance and Sears resonance terms in the Hamiltonian matrices. The Windows program RT3, written in Visual Basic 6.0 with a Fortran DLL engine for the numerically intensive computations, facilitates the construction and editing of input files and comparisons of input and output. For very large calculations, the Fortran code may be run as a stand-alone program on mainframe or other computers, but the Windows version offers significant advantages for common usage.