Photoionisation cross-sections of HCN, HNC, and HNO

The primary aim of this work is to provide accurate photoionisation data for HCN, HNC, and HNO, including absolute total photoionisation cross sections and state-resolved partial cross sections. In addition, near-threshold structures in the photoionisation spectra are resolved with high precision. In our calculations we employed a multichannel wavefunction constructed within the R-matrix framework, using configuration interaction to account for electronic correlation. The continuum is represented by a set of B-spline orbitals, enabling a highly accurate description of the scattering electron. This approach yields a more precise treatment of both the bound and continuum states compared with previous studies. We present total photoionisation cross sections from the ground states of HCN, HNC, and HNO, along with the partial cross sections that lead to various excited states of ions for photon energies from the ionisation thresholds up to 50 eV. A rich set of resonance features—absent in earlier calculations—is revealed near the ionisation thresholds for all three molecules. The resulting cross-section dataset is expected to be sufficiently accurate and comprehensive for most current modelling applications involving photon–molecule scattering for these systems.