High-resolution, near-infrared CW-CRDS, and <i>ab initio</i> investigations of N₂O–HDO

<div><p>We have investigated the N₂O–HDO molecular complex using <i>ab initio</i> calculations at the CCSD(T)-F12a/aug-cc-pVTZ level of theory and using cavity ring-down spectroscopy to probe an HDO/N₂O/Ar supersonic jet around 1.58 μm. A single <i>a</i>-type vibrational band was observed, 13 cm⁻¹ redshifted compared to the OH+OD excited band in HDO, and 173 vibration-rotation lines were assigned (<i>T</i>_rot ≈ 20 K). A weighted fit of existing microwave and present near infrared (NIR) data was achieved using a standard Watson's Hamiltonian (σ = 1.26), producing ground and excited states rotational constants. The comparison of the former with those calculated <i>ab initio</i> suggests a planar geometry in which the OD rather than the OH bond in water is almost parallel to NNO. The equilibrium geometry and dissociation energy (<i>D_e</i> = –11.7 kJ/mol) of the water–nitrous oxide complex were calculated. The calculations further demonstrate and allow characterising another minimum, 404 cm⁻¹ (Δ<i>E</i>₀) higher in energy. Harmonic vibrational frequencies and dissociation energies, <i>D</i>₀, were calculated for various conformers and isotopic forms of the complex, in both minima. The absence of N₂O–D₂O from dedicated NIR experiments is reported and discussed.</p>