High-resolution IR spectroscopy of the N2O-H2O and N2O-D2O van der Waals complexes

We report high-resolution infrared vibrational-rotational spectra of the weakly bound complexes N2O-H2O and N2O-D2O in the higher frequency N2O stretching mode region (v(3) = 2223.756693(124) cm(-1)). The measurements were carried out using a free jet expansion in combination with a lead salt diode laser spectrometer. Rotational constants, quartic centrifugal distortion constants, and band origins have been derived for both isotopomers. The geometrical structure is determined using isotopic substitution. The deduced structure shows evidence for a second hydrogen bond interaction within the complex. The nonrigidity of the complexes gives rise to an internal rotation of the water molecule around its own C-2v symmetry axis. For N2O-H2O, a tunneling splitting arising from this internal motion has been observed in the spectra. According to symmetry considerations, the observed splitting in the spectrum of N2O-H2O corresponds to the difference between the tunneling frequencies in the ground and vibrationally excited states. (C) 2002 Elsevier Science (USA).