is a major absorber in cool stars [@00AlHaS1.TiO; @13DaKuPl.TiO]. There are TiO line lists available from Schwenke [@98Scxxxx.TiO] and Plez [@98Plxxxx.TiO]. However it would appear that these line lists are incomplete; in particular there are missing bands that have been observed in the laboratory [@99RaBeDu.TiO]. Furthermore, recent exoplanet studies suggest that the line frequencies are too inaccurate for high resolution studies [@15HoDeSn.TiO].

Data Provided
=============

The original aim of the ExoMol project was the provision of extensive line lists of energy levels, and hence transition frequencies, and Einstein $A$ coefficients from which transition intensities and related information can be computed. The original ExoMol data structure [@jt548] provided precisely for these data in a concise manner. The demands on and utility of the data provided by the project has led us to expand the scope of the database. In this section we outline the new data provision and in the following sections we formally define the new data structures employed for this purpose.

Extended states file
--------------------

There are other properties of a molecular state that can be computed by ExoMol which we now propose to store. The first of these is the radiative lifetime of each individual state, which can 