Terahertz vibration–rotation-tunneling (VRT) spectroscopy of the d6-water trimer: Complete characterization of the 2.94 THz torsional band (kn = ±21 ← 00)

We report the measurement and analysis of the complete perpendicular kn = ±21 ← 00 (D2O)3 torsional band (origin 2940.9376(3) GHz), the upper state of which is the highest-energy (98.09912 cm−1) torsional state yet observed. All known torsional transitions were included in a new global analysis of the six observed torsional bands, using the effective Hamiltonians derived by van der Avoird et al. [M. R. Viant, M. G. Brown, J. D. Cruzan, R. J. Saykally, M. Geleijns, A. van der Avoird, J. Chem. Phys. 110 (1999) 4369; A. van der Avoird, E. H. T. Olthof, P. E. S. Wormer, J. Chem. Phys. 105 (1996) 8034]. The experimental results will facilitate the descriptions of three-body interactions in water intermolecular potential energy surfaces (IPSs).