High-Resolution IR Spectroscopy of the N 2O–H 2O and N 2O–D 2O van der Waals Complexes

Abstract

We report high-resolution infrared vibrational–rotational spectra of the weakly bound complexes N 2O–H 2O and N 2O–D 2O in the higher frequency N 2O stretching mode region (ν 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 2 v symmetry axis. For N 2O–H 2O, 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 N 2O–H 2O corresponds to the difference between the tunneling frequencies in the ground and vibrationally excited states.