Low frequency motions of water isolated in low temperature matrices

Far infrared spectra of monomer H₂O, D₂O, HOD in argon and nitrogen and of H₂O in krypton and methane are recorded at different temperatures. Assignments of the bands to rotational and translational motions are given for argon and krypton on the basis of rotational constants, derived from mid infrared vibration rotation matrix spectra. Motions of water in nitrogen are interpreted as librations around the OH bond axes, because the HOD spectra do not fit the picture of librations around the proper rotational axes.