High-accuracy water potential energy surface for the calculation of infrared spectra

Transition intensities for small molecules such as water and CO 2 can now be computed with such high accuracy that they are being used to systematically replace measurements in standard databases. These calculations use high-accuracy ab initio dipole moment surfaces and wave functions from spectroscopically determined potential energy surfaces (PESs). Here, an extra high-accuracy PES of the water molecule (H 2 16 O) is produced starting from an ab initio PES which is then refined to empirical rovibrational energy levels. Variational nuclear motion calculations using this PES reproduce the fitted energy levels with a standard deviation of 0.011 cm −1 , approximately three times their stated uncertainty. The use of wave functions computed with this refined PES is found to improve the predicted transition intensities for selected (problematic) transitions. A new room temperature line list for H 2 16 O is presented. It is suggested that the associated set of line intensities is the most accurate available to date for this species. This article is part of the theme issue ‘Modern theoretical chemistry’.