Theoretical rotation-vibration spectroscopy of {\it cis}- and {\it trans}-diphosphene (P${}_2$H${}_2$) and the deuterated species P${}_2$HD

Growing astronomical interest in phosphorous (P) chemistry is stimulating the search for new interstellar P-bearing molecules; a task requiring detailed knowledge of the microwave and infrared molecular spectrum. In this work, we present comprehensive rotation-vibration line lists of the \cis- and \trans-isomers of diphosphene (P${}_2$H${}_2$). The line lists have been generated using robust, first-principles methodologies based on newly computed, high-level \ai\ potential energy and dipole moment surfaces. Transitions are considered between states with energies up to $8000$~cm${}^{-1}$ and total angular momentum $J\le 25$. These are the first-ever line lists to be reported for P${}_2$H${}_2$ and they should significantly facilitate future spectroscopic characterization of this system. The deuterated species \trans-P${}_2$HD and the effect of its dynamic dipole moment on the rovibrational spectrum is also discussed.