Knowledge Bank

High resolution spectra, recorded either on Fourier transform or classical grating spectrometers, allows precise determination of vibration-rotation energy levels of $ {H_{2}}{^{16}}O$. Rotational levels of the (000), (020), (100), (001) and (030) states have been obtained with a good accuracy. The task of fitting these experimental levels with a theoretical model is difficult. We report a fit of the ground state rotational levels with Watson ‘s Hamiltonian (141 levels up to J = 15, 21 constants, standard deviation: $2.10-3$ $cm-1)$. We have attempted to perform the calculation of the Coriolis interaction between (100) and (001) treating (020) alone. From this, it appears that it is necessary to treat the three interacting states simultaneously. The first treatment has however the advantage of providing a good set of initial parameters for the iterative refinement used to obtain the final parameters of the three interacting states.