Torsion vibrations tunneling rotation

In case of the related complex (HCl) comparatively few accurate spectroscopic investigations have been performed to date. Very recently, Blake et al. 713/ reported a far infrared rotation-tunnelling spectrum. In a related investigation Moazzen-Ahmadi et al. 714/ analyzed the torsional vibration of (HC1)2 Fundamental frequencies of the... 

Torsional barriers are referred to as n-fold barriers, where the torsional potential function repeats every 2n/n radians. As in the case of inversion vibrations (Section 6.2.5.4a) quantum mechanical tunnelling through an n-fold torsional barrier may occur, splitting a vibrational level into n components. The splitting into two components near the top of a twofold barrier is shown in Figure 6.45. When the barrier is surmounted free internal rotation takes place, the energy levels then resembling those for rotation rather than vibration. 

FIGURE 11 Vibrational-rotational-tunneling (VRT) spectra of the water dimer. AT, acceptor twist (A ) AW, acceptor wag (A) DT, donor torsion N )] GS, ground state (A). Broken lines A symmetry and solid lines, A symmetry with respect to the equilibrium structure. K = 0, rotational ground state, K = 1, first excited state. The calculated results are from Groenenboom etal. (2000), while the experimental data are from Braly etal. (2000). 

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