Rotational tunneling splittings

Calculations of Rotational Tunneling Splittings. The calculation of tunnel splittings and the comparison with experiment offer a severe test of the knowledge of the potential energy surface. As all measurements are made at... 

In most cases the ground-state rotational tunnel splitting, as well as the two transitions to the split excited librational state, are observed. Because the tunnel splittings (typically 1-10 cm-1) can be measured with much better accuracy than the librational transitions, the value for the barrier height V2 is usually extracted from the former. Higher terms in the expansion of the potential are introduced only if the librational transitions derived do not agree well with other observations. For... 

This distortion about M is sensitive to steric effects or crystal-packing forces, e.g., the same complex can have slightly different molecular structures and therefore different barriers to H2 rotation when crystallized with different counterions or lattice solvent molecules. The rotational tunnel splitting (17 cm-1) is larger [and the barrier is thus lower (Table 6.1)] for Mo(CO)(H2)(dppe)2-2-toluene solvate than the... 

TABLE 1. Rotational tunnel splitting (to, cm ) and derived rotational barriers (E, kcal/ mol) for dihydrogen complexes. 

Figure Bl.4.9. Top rotation-tunnelling hyperfine structure in one of the flipping inodes of (020)3 near 3 THz. The small splittings seen in the Q-branch transitions are induced by the bound-free hydrogen atom tiiimelling by the water monomers. Bottom the low-frequency torsional mode structure of the water duner spectrum, includmg a detailed comparison of theoretical calculations of the dynamics with those observed experimentally [ ]. The symbols next to the arrows depict the parallel (A k= 0) versus perpendicular (A = 1) nature of the selection rules in the pseudorotation manifold.

Fully Coupled Six-Dimensional Calculations of the Water Dimer Vibration-Rotation-Tunneling States with a Split Wigner Pseudo Spectral Approach. 

The symmetry and height of the rotational barriers and hence the tunnel splittings depend strongly on the orientation of the molecule and its adsorption site. The results of these measurements (a higher resolution experiment is planned) when combined with model calculations based on empirical atom-atom potentials (see below) may be able to provide corroborative evidence for the orientation of an adsorbed molecule as well as details of the molecule-substrate interaction. The principal obstacle to a wider application of the technique may simply be the small number of adsorbed systems in which these tunnel splittings can be observed. 

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