Potential energy surface rotational tunneling

Nonpolar and dipolar altitudinal rotors (compounds 2 and 3 in Fig. 17.3) have been synthesized. 19F NMR spectroscopy showed that the barrier to rotation in 3 was extremely low in solution. Both systems have then been immobilized on Au(l 11) surfaces and studied with a variety of techniques.57 The results obtained indicated that for a fraction of molecules the static electric field from the scanning tunneling microscopy (STM) tip could induce an orientation change in the dipolar rotor but not in the nonpolar analog (for a recent example of an azimuthal molecular rotor controlled by the STM tip, see Reference 58). Compound 3 can exist as three pairs of helical enantiomers because of the propeller-like conformation of the tetra-arylcyclobutadienes. For at least one out of the three diastereomers, an asymmetric potential energy surface can be predicted by molecular dynamics simulations on application of an alternating electric field.55... 

Elrod, M. J., and Saykally, R. J., Determination of the intermolecular potential energy surface for (HClj from vibration-rotation-tunneling spectra, J. Chem. Phys. 103,933-949 (1995). Latajka, Z., and Scheiner, S., Structure, energetics and vibrational spectra ofH-bonded systems. Dimers and trimers ofHFand HCl, Chem. Phys. 122, 413 30 (1988). 

Saykally, Determination of the intermolecular potential energy surface for (HC1)2 from vibration-rotation-tunneling spectra, J. Chem. Phys., 103 1995) 933-949. 

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... 

It is quite straightforward to perform quasiclassical trajectory computations (QCT) on the reactions of polyatomic molecules providing a smooth global potential energy surface is available from which derivatives can be obtained with respect to the atomic coordinates. This method is described in detail in Classical Trajectory Simulations Final Conditions. Hamilton s equations are solved to follow the motion of the individual atoms as a function of time and the reactant and product vibrational and rotational states can be set or boxed to quantum mechanical energies. The method does not treat purely quantum mechanical effects such as tunneling, resonances. or interference but it can treat the full state-to-state, eneigy-resolved dynamics of a reaction and also produces rate constants. Numerous applications to polyatomic reactions have been reported. ... 

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