  Zirconium monoxide (ZrO) absorption lines define rare S-type stars and are
currently being sought on exoplanets. Successful detection is dependent on an
accurate and comprehensive line list, with existing data not ideal for many
applications. Specifically, the Plez \etal{} line list is near-complete but has
insufficient accuracy for high-resolution cross-correlation, while the Sorensen
\& Bernath data has high accuracy but only considers a small number of spectral
bands. This article presents a novel spectroscopic model, variational line list
and trihybrid line list for the main \ZrO{} isotopologue, as well as
isotopologue-extrapolated hybrid line lists for the \isoa{}, \isob{}, \isoc{},
\isod{}~and \isoe{} isotopologues. These were constructed using \DUO{} based on
icMRCI-SD/CASSCF~\abinitio{} electronic data calculated using \MOLPRO{},
experimental energies obtained from a previous \Marvel{} data compilation and
perturbative energies from Sorensen \& Bernath. The new \ZrO{} \EXOMOL{}-style
trihybrid line list, \LLname{}, comprises \noenergies{} energies
(\noMaenergies{} experimental) and \notransitions{} transitions up to
30,000~\cm{} (333~nm) between ten low-lying electronic states (\ZrOX{},
\ZrOaa{}, \ZrOA{}, \ZrObb{}, \ZrOB{}, \ZrOC{}, \ZrOdd{}, \ZrOee{}, \ZrOff{} and
\ZrOF{}). The inclusion of experimental energy levels in \LLname{} means ZrO
will be much easier to detect using high-resolution ground-based telescopes in
the 12,500 -- 17,500~\cm{} (571 -- 800~nm) spectral region. The inclusion of
variational energy levels means that the ZorrO line list has very high
completeness and can accurately model molecular absorption cross-sections even
at high temperatures. The \LLname{} data will hopefully facilitate the first
detection of ZrO in the atmosphere of a hot Jupiter exoplanet, or alternatively
more conclusively exclude its presence.
