Hyperfine-Resolved Near-Infrared Spectra of H217O.

Mattia Melosso,Michael E Harding,Meissa L Diouf,Frank M J Cozijn,Luca Bizzocchi,Cristina Puzzarini,Wim Ubachs

doi:10.1021/acs.jpca.1c05681

Abstract

Huge efforts have recently been taken in the derivation of accurate compilations of rovibrational energies of water, one of the most important reference systems in spectroscopy. Such precision is desirable for all water isotopologues, although their investigation is challenged by hyperfine effects in their spectra. Frequency-comb locked noise-immune cavity-enhanced optical-heterodyne molecular spectroscopy (NICE-OHMS) allows for achieving high sensitivity, resolution, and accuracy. This technique has been employed to resolve the subtle hyperfine splittings of rovibrational transitions of H217O in the near-infrared region. Simulation and interpretation of the H217O saturation spectra have been supported by coupled-cluster calculations performed with large basis sets and accounting for high-level corrections. Experimental 17O hyperfine parameters are found in excellent agreement with the corresponding computed values. The need of including small hyperfine effects in the analysis of H217O spectra has been demonstrated together with the ability of the computational strategy employed for providing quantitative predictions of the corresponding parameters.

Highlights

Hyperfine parameters constitute an important source of information on physicochemical molecular properties related to electron densities and electronic structure
Nuclear spin-rotation interaction and their corresponding constants provide, instead, insight into the paramagnetic part of the nuclear magnetic shielding constants, and this was the motivation for investigating the hyperfine structure (HFS) of the rotational spectrum of water isotopologues containing an 17O.1,2
We extend our previous work on the saturation spectroscopy of water[14] to the 17O-containing species, thereby using the advanced capabilities of a frequency-comb locked noise-immune cavity-enhanced optical-heterodyne molecular spectroscopy (NICE-OHMS) setup to resolve, for the first time, the HFS of rovibrational transitions of H217O

Summary

■ INTRODUCTION

Hyperfine parameters constitute an important source of information on physicochemical molecular properties related to electron densities and electronic structure. The vibrational corrections were calculated as the difference between the vibrationally averaged and the equilibrium values, both at the CCSD(T) level in conjunction with the aug-ccpCVQZ25−27 basis set. Scalar relativistic corrections to the nuclear quadrupole-coupling tensors (ΔREL term) have been evaluated using second-order direct perturbation theory (DPT2)[30] at the CCSD(T)/aug-ccpCV6Z level. As in previous studies focusing on the (000) vibrational ground state,[1,2] the DVR-QAK31 scheme has been employed to compute the vibrational corrections to equilibrium values In this approach, the treatment of vibrational effects is based on the variation principle and on the use of the so-called Watson Hamiltonian,[32] given in terms of rectilinear dimensionless normal coordinates, and fully accounts for Coriolis interactions and anharmonic effects in the potential. The measurements have been carried out under steady gas flow conditions, at pressures in the range of 0.1−0.3 Pa,

■ RESULTS AND DISCUSSION

■ ACKNOWLEDGMENTS

■ REFERENCES