Measurement of the perpendicular rotation-tunneling spectrum of the water dimer by tunable far infrared laser spectroscopy in a planar supersonic jet

Abstract

Fifty-six transitions from the K=1 lower→K=2 lower tunneling–rotation band of water dimer have been measured and assigned at 22 cm−1 by direct absorption spectroscopy in a cw planar supersonic jet expansion using a tunable far infrared laser spectrometer. Two different models were used to fit the data and several spectroscopic constants were determined for the upper and lower states. This work supports the local IAM model recently proposed by Coudert and Hougen for the hydrogen bond tunneling dynamics of the water dimer. This model includes four different tunneling motions, all of which contribute to the observed tunneling splittings. This is the most complicated hydrogen bonded system considered to be well understood at this time, at least in the lowest few K states.

The water dimer I: Experimental characterization

“…The first terahertz (far-infrared) spectrum of the gaseous water dimer was observed near 22 cm −1 for (H 2 O) 2 by Busarow et al in 1989 using the Berkeley-tunable far-IR laser spectrometer coupled with a planar supersonic jet [75]. This work was contemporary with the microwave study of (H 2 O) 2 .…”

Conformational Landscape of the 1/1 Diacetyl/Water Complex Investigated by Infrared Spectroscopy and ab Initio Calculations

“…In this context, the spectroscopic study of small water clusters produced at very low temperature in nearly isolated conditions proved to be determinant for improving the building of reliable intermolecular potential energy surfaces based on a back and forth procedure between experiment and theory. As a first step toward this objective, we can cite the challenging studies based on jet-cooled far-and near-IR laser and microwave spectroscopy which yielded new insights into the tunneling motions of the water dimer [4][5][6] and allowed to determine a polarisable water pair potential. 7 The huge capacity of water to establish hydrogen bonds with the close environment owing to its twice role of hydrogen-bond donor and acceptor would suggest to use a molecular approach based on a step by step increase of the size of hydrates for most studies related to the hydration process of organic species.…”

Water Dimers in the Atmosphere II: Results from the VRT(ASP-W)III Potential Surface

“…The dimer tunneling splittings from hydrogen bond rearrangements and the intermolecular vibrational frequencies provide a sensitive probe of the complex water IPS, 30,31 and such measurements have been made extensively by our laboratory. [32][33][34] The VRT(ASP-W)III potential was generated by fitting six of the exchange-repulsion parameters in ASP-W 29 to (D 2 O) 2 microwave and far-IR transitions using a nonlinear least-squares regression procedure. 20 The ASP-W potential has 72 parameters, but it was found previously that accurate fits could be produced by varying only a few of the exchange-repulsion parameters.…”