RESONANCE RAMAN EFFECT IN SOLUTIONS

Abstract

The experimental observation of the resonance Raman effect in solutions is restricted by the absorption of the sample. Under ordinary circumstances one is required to compromise between absorption and emission of the scattered light. Using a rotating Raman cell we were able to reduce the diffuseness of the incident beam due to the thermal lense effect and increase the observed Raman intensity by a factor of about ten. The Resonance Raman spectra of some highly coloured inorganic compounds (e.g. $KMnO_{4}$, $l_{2}$) in dilute solutions are reported. The spectra were excited with the blue and green lines of an argon ion laser. In the case of the potassium permanganate solutions seven overtones of the $\nu_{1}$ ($A_{1}$) mode of the $MnO_{4}$ ion ($T_{4}$ symmetry) were observed as well as some combination tones $n\nu_{1}$ ($A_{1}) + \nu_{2}$ ($F_{2}$). From the wavenumbers of the overtones of $\nu_{1}$ the dissociation energy of the $MnO^{-}_{4}$ ion has been estimated. Overtone sequences of the $I_{2}$ vibration up to the 15th harmonic were recorded and compared with the results of the Resonance Raman spectra of $I_{2}$ in the gas phase.