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

Abstract

We have investigated the N₂O–HDO molecular complex using ab initio 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 a-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 (T_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 ab initio 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 (D_e = –11.7 kJ/mol) of the water–nitrous oxide complex were calculated. The calculations further demonstrate and allow characterising another minimum, 404 cm⁻¹ (ΔE₀) higher in energy. Harmonic vibrational frequencies and dissociation energies, D₀, 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.

Keywords:

• cavity ring-down spectroscopy
• overtone spectroscopy
• ab initio calculation
• molecular complex

Acknowledgements

We are deeply indebted to S. Novick and his team (Wesleyan University) and to W. Klemperer (Harvard) for reinvestigating the studied dimer to help us understand its structure.

Notes

1. During the course of the present work, we did stimulate a new MW investigation of HDO–NNO complex, by Novick and co-workers (Wesleyan U), which seems to confirm that the DO rather than the HO bond is the one almost parallel to the NNO linear species in the experimentally probed species, thus confirming the present results. These new, still unpublished results are based on a detailed structural analysis from the MW constants as well as on new hyperfine quadrupole data and analysis ([36]).

Additional information

Funding

We thank the ‘Communauté Wallonie-Bruxelles (ARC)’ for financial support.