Frequency measurement of pure rotational transitions in the v2Â =Â 1 state of H2O

Frequencies of pure rotational transitions in the v2 = 1 vibrationally excited state of H216O were measured with a tunable far-infrared spectrometer in the frequency range of 0.5-5 THz. Molecular parameters of Watson's A-reduced Hamiltonian have been obtained to reproduce the observed frequencies.