Diatomic is a spectral simulation program for diatomic molecules. It allows the user to simulate laser-induced fluorescence, absorption, and emission spectra of diatomic molecules. The program assumes the electric dipole selection rules.

Diatomic Features:
1. Simulation of any intermediate coupling case between the Hund case (a) and Hund case (b).
2. Taking account of leading centrifugal corrections (up to Lv) as well as fine structure interactions (spin-orbit, spin-spin and spin-rotation) in the simulation.
3. Allowing up to 32 vibrational terms for each band constant.
4. Using either the user specified Franck-Condon factors (FCF) or calculating the FCFs from RKR potentials derived from the input vibrational and rotational constants.
5. Taking account of the Lambda-type doubling up to L = 2,'s = 2 in the simulation.
6. Taking account of nuclear spin statistics in the simulation.
7. Taking account of excitation-detection geometry, polarizations, and spatial alignment of the initial-state angular momentum in LIF simulations.
8. Supporting various lineshapes: Gaussian, Lorentzian, and Voigt lineshapes are supported for LIF and absorption. Instrumental slit transmission functions (rectangular and grating diffraction function) are supported for emission.
9. Displaying both the graphical spectrum or RKR potential curves, and text results on an integrated user interface.
10. Automatic labeling of rotational lines on the simulated graphical spectrum.
11. Supporting basic graphical manipulations and comparison of the simulated spectrum with an user imported spectrum.
12. Customizing and printing reports.

The license of this software is Freeware, you can free download and free use this graphing software.