The origin of anti-resonance in preresonance Raman scattering

Abstract

The anti-resonance phenomenon in Raman scattering was studied in the preresonance region of an allowed electronic transition. It is shown that the anti-resonance in the scattering of both totally and non-totally symmetric modes can be explained in terms of an analytical model. The necessary and general conditions for obtaining an anti-resonance are derived. The importance of comparing resonance and preresonance data (showing the antiresonance e †ect), in order to obtain reliable molecular parameters from the experiments, is demonstrated. For both totally and non-totally symmetric modes it is shown that, depending on the nature and number of the electronic states that contribute to the scattering, the anti-resonance in the excitation proÐle may be followed by a dramatic dispersion in the depolarization ratio. By comparing model calculations of the depolarization ratio and the excitation proÐle with experimental data, it is shown that both of these quantities are needed in order to discriminate between di †erent theoretical models.

Survival of molecular information under surfaced‐enhanced resonance Raman (SERRS) conditions

“…Antiresonance in naphthalene and anthracene, belonging to the point group D 2h , has been studied experimentally by Ito and Suzuka [33] ; Schmid et al [34] ; Ohta and Ito [35] ; Ehland et al [36] and theoretically by Hassing, [37] and Zheng and Wei. [38] The intensity of the measured REP for both symmetric and asymmetric modes will normally increase when the excitation wavenumber is approaching an electronic transition.…”

“…Although different molecular sources of antiresonance exist, depending on the molecular properties, antiresonance is basically due to the destructive interference between the various contributions to the Raman tensor, each of which is determined by a state tensor and the corresponding complex energy denominator. The general conditions for obtaining antiresonance [37] in the pre-resonance region of an electronic transition are that the molecule must contain at least one pair of non-degenerate vibronic states that contribute to the scattering. These states must have state tensors with different signs, and at the same time the state tensor of the state with the higher energy should have a larger magnitude than the state tensor at lower energy.…”

“…[37] Thus, the vibronic state tensors belonging to the B 1u electronic state are of the form S |eνe zz , whereas the vibronic state tensors belonging to the B 2u electronic state are of the form S |e ν e yy . The expressions for the vibronic state tensors are found by adopting the adiabatic approximation and substituting first-order expansions www.interscience.wiley.com/journal/jrs of the electronic transition moments in nuclear coordinates in Eqn (3).…”

“…When considering the same scenario for an asymmetric vibration, it follows from the results obtained from Refs [33,36,37] that the experimental REP can be fitted by using a model based on the two electronic states used above. This model, however, predicts a strong dispersion of the DPR in the region of the antiresonance, which is not observed experimentally.…”

Anti-resonance in naphthalene and anthracene, determined from highly resolved and polarized pre-resonance Raman excitation spectra

“…When the symmetry is the same the components and in the numerator must be interchanged. 7 For a non-degenerate, non-totally symmetric Raman mode, the following expression for the two non-vanishing tensor invariants  1 and  2 can be derived: 7…”