PGOPHER: A program for simulating rotational, vibrational and electronic spectra

- Easy-to-use graphical interface for assigning and understanding molecular spectra.
- Simulates rotational and vibrational structure of many types of molecular spectra.
- Fits molecular properties to line positions or spectral contours.
- Handles linear molecules and symmetric and asymmetric tops.
- Handles perturbations, nuclear and electron spin, and electric and magnetic fields.

The pgopher program is a general purpose program for simulating and fitting molecular spectra, particularly the rotational structure. The current version can handle linear molecules, symmetric tops and asymmetric tops and many possible transitions, both allowed and forbidden, including multiphoton and Raman spectra in addition to the common electric dipole absorptions. Many different interactions can be included in the calculation, including those arising from electron and nuclear spin, and external electric and magnetic fields. Multiple states and interactions between them can also be accounted for, limited only by available memory. Fitting of experimental data can be to line positions (in many common formats), intensities or band contours and the parameters determined can be level populations as well as rotational constants. pgopher is provided with a powerful and flexible graphical user interface to simplify many of the tasks required in simulating, understanding and fitting molecular spectra, including Fortrat diagrams and energy level plots in addition to overlaying experimental and simulated spectra. The program is open source, and can be compiled with open source tools. This paper provides a formal description of the operation of version 9.1.