The electronic structures of the nonresonant Raman excited virtual states of 2-aminopyridine by 632.8 and 514.5nm excitations as evidenced by the bond polarizabilities

Intra-molecular enantiomerism in R-(+)-Limonene as evidenced by the differential bond polarizabilities

We propose an algorithm to obtain the differential bond polarizabilities from the Raman and Raman optical activity (ROA) spectral intensities. The signs of the differential bond polarizabilities of R-Limonene demonstrate that there is intra-molecular enantiomerism in its six membered ring structure. That is, the signs of the differential bond polarizabilities around the six membered ring are inversed under an intra-molecular mirror reflection. This is similar to what happens in the right and left handed chiral isomers under a mirror conversion.

Stereostructural implication by the differential bond polarizability: ROA intensity study of chiral s 2-amino 1-propanol

The bond polarizability and differential bond polarizability are introduced to interpret the Raman and Raman optical activity (ROA) intensities, calculated by the ab initio method. Chiral S 2-amino 1-propanol is taken as a model molecule. Through these bond polarizabilities, we observe that symmetric and antisymmetric coordinates are, respectively, more significant in Raman and ROA. It is noted that in S 2-amino 1-propanol those bonds lying on a common plane share the same differential bond polarizability sign while that of the asymmetric C-H bond which protrudes out of the plane possesses the opposite sign. We conclude that ROA can offer more stereostructural implications than Raman and that the differential bond polarizability is potentially the appropriate parameter in interpreting the 3D configuration of a molecule.

The asymmetry of (-)α-pinene as revealed from its raman optical activity spectrum

An algorithm is employed to retrieve the differential bond polarizabilities of the C-C bonds from the Raman optical activity (ROA) spectrum of (-)α-pinene. (-)α-pinene possesses two asymmetric centers (carbon atoms) and a local mirror symmetry. These differential bond polarizabilities show the characteristics of the asymmetry around the asymmetric carbons with respect to the mirror reflection. This analysis is accompanied along with the ROA mode signatures and the calculated β(G ')(2) and β(A)(2) which show the ROA coupling mechanisms involving the electric/magnetic dipoles and the electric dipole/quadrupole, respectively.

The charge excitation in the Raman process as correlated from a classical theory for Raman optical activity: the case study of (+)-(R)-methyloxirane

We developed a classical algorithm to calculate the spectral signs in the Raman optical activity (ROA) spectrum. In this algorithm, the charge re-distributions among the bonds, which are associated to the bond polarizabilities, are included. For (+)-(R)-methyloxirane, we found that if these bond polarizabilities are attributed to the atoms and are properly scaled in order to be combined with the Mulliken charges on the atoms in the ground state, then the experimental ROA spectral signs can be well reproduced. Furthermore, in this process, we are able to determine that around 20% of the electrons in the molecule are excited in the Raman process.

Raman intensity interpretation of pyridine liquid and its adsorption on the Ag electrode via bond polarizabilities

The temporal bond polarizabilities of pyridine adsorbed on the Ag electrode under various applied voltages are obtained from their surface enhanced Raman intensities. In so doing, the delicate bond behaviors of pyridine molecule in the surface enhanced Raman process are well demonstrated, including the effects by the charge transfer and electromagnetic mechanisms. Furthermore, the adsorption effect is well reflected by the bond polarizabilities after relaxation as contrasted with the calculated bond electronic densities in the ground state. The work of pyridine liquid is also shown because its comparison with that under adsorption deepens our understanding of the Raman process. Though the method is semi-classical and simple as contrasted with those based on the quantum chemistry, it indeed offers us a very clear physical picture. This work demonstrates that this approach is quite universal for the Raman active systems even under adsorption as far as their Raman profiles are well measured.

The significance of the temporal bond polarizabilty relaxation of 2- and 3-aminopyridine by 514.5 nm excitation for the nonresonant Raman virtual states

Our algorithm [B. Tian, G. Wu, G. Liu, J. Chem. Phys. 87 (1987) 7300] is introduced to obtain the temporal bond polarizabilities of 2- and 3-aminopyridine from their Raman intensities, which supply fruitful electronic information of the nonresonant Raman excited virtual states. The study shows that the excited charges tend to flow to the molecular periphery due to electronic repulsion and most of their relaxations show a single exponential decaying behavior, though some are exceptional. The characteristic times corresponding to the relaxations of the peripheral C-H and branching C-N bond polarizabilities are, in general, shorter than those of the skeletal C-C/C-N bonds. There is also evidence that only electrons from part of the occupied MO's are excited and contribute to the Raman excited virtual states.