Supplementary material to the manuscript: General variational approach to nuclear-quadrupole coupling in rovibrational spectra of polyatomic molecules Composed of three files: 1. nh3_efg.zip - compressed folder containing Fortran 90 program, together with the input/output examples and README file, for computing the electric field gradient tensor of NH3. 2. nh3_linelist.tar - contains compressed file with the rovibrational line list of NH3 with quadrupole coupling components, together with the Python scripts for extracting desired transitions and README file. nh3_qmom_suppinfo.pdf - PDF file with equations skipped in the main manuscript.

Besides DESY, this work has been supported by the excellence cluster "The Hamburg Center for Ultrafast Imaging—Structure, Dynamics and Control of Matter at the Atomic Scale" of the Deutsche Forschungsgemeinschaft (CUI, DFG- EXC1074).