Isotopic substitution effects

In this paper, we apply the three algorithms to the determination of the V effect of the torsional levels of hydrogen peroxide. The size of this molecule is optimum for the comparison of the three methods. In addition, a previous study shows that torsion of the central bond can be separated from the rest of the vibrational modes, thereby simplifying the problem. Finally, the torsional pseudopotential ofD202 is also calculated for determining the isotopic substitution effects. The experimental data are from Camy-Peiret et al [15]. 

MOPAC AMI AMI is used in the electronic part of the calculation to obtain molecular orbitals, the heat of formation and its derivative with respect to molecular geometry. MOPAC calculates the vibrational spectra, thermodynamic quantities, isotopic substitution effects and force constants for molecules, radicals, ions,... 

The kinetics of formation in liquid Kr are inconsistent with a dissociative mechanism but are rationalized by an equilibrium between Kr and cyclohexane complexes prior to OA. vco for Cp Rh(CO)(CyH) is unobservable, probably because of overlap with that of Cp Rh(CO)(Kr).135 Use of cyclohexane- 2 to examine isotopic substitution effects shows an inverse (Kh/Kd = ca 0.1) for the interconversion of Kr and alkane adducts, i.e C6D12 binds more strongly to M than C6H12.116 Although initially contrary to expectations based on simple zero-point energy arguments, this is explainable by the increase in the number of vibrational modes for bound alkane versus free alkane (see Section 7.5.2). As observed for the formation of H2 complexes, the inverse effect is perfectly consistent with formation of an alkane [Pg.400]

Nuclear motions give rise to isotopic substitution effects and temperature dependence of coupling constants. For rigid molecules, such effects are usually small and their observation requires the use of very accurate experimental techniques. Within the Bom-Oppenheimer approximation, both effects may... 

The IR and Raman spectra of the tetrahedral molybdates, tetrathiomolybdates and tetraselenomolybdates have also received study. For the Ta, tetrahedral dianion Mo04, the two stretching modes (y4i and F2) are Raman active and one (F2) is IR active as weU. Bending modes are of E and F2 symmetry, and while both are Raman active, only Fi is IR active. Bands at 897 and 837 cm have been assigned as stretches, whereas those at 325 and 317cm are assigned to bends. Detailed vibrational analyses of MoC have included Mo/ Mo isotopic substitution effects and polarized IR measurements. Studies on MoOsS " and Mo02S reveal the v(Mo—O) bands expected for and C-t structures, respectively. ... 

Isotopic substitution effects can be studied using the DRC. This would allow, for example, kinetic isotope effects to be calculated. 

---