Raman Spectroscopy of Toluene and Fluorescence Spectroscopy of Rhodamine 6G - Lab Report Example

In Raman spectroscopy, light and matter interacts. Both IR and Raman vibrational bands are described by their frequency (i.e energy), band shape, and intensity. At low frequencies, the fingerprint region is found for most compounds. Raman spectroscopy is much easier to use at low frequencies compared to IR, this is because at low frequencies very many bands are visible on the spectrum. With Raman spectroscopy, it is possible to reject the laser beam at low frequency modes; this would minimize the bands that are seen at the fingerprint region.

With IR, this is not possible, and as a result the spectrum cannot be refined to reduce the congestion of peaks. Toluene (methylbenzene) has a CH3 group attached to the benzene ring, for IR spectroscopy, the CH3 group exists at just below 1500 cm-1. This is just at the start of the fingerprint region; therefore Raman spectroscopy would be much better at elucidating its structure over IR. Fluorescence is a spectrochemical method of analysis where the molecules of the analyte are excited by irradiation at a certain wavelength and emit radiation of a different wavelength.

The emission spectrum provides information for both qualitative and quantitative analysis. When light of an appropriate wavelength is absorbed by a molecule (i.e., excitation), the electronic state of the molecule changes from the ground state to one of many vibrational levels in one of the excited electronic states. The excited electronic state is usually the first excited singlet state, S1 (Figure 1). Once the molecule is in this excited state, relaxation can occur through several processes.

Fluorescence is one of these processes and results in the emission of light. Fluorescence corresponds to the relaxation of the molecule from the singlet excited state to the singlet ground state with emission of light. Fluorescence has short lifetime (~10-8 sec) so that in many molecules it can compete favorably with collision deactivation, intersystem crossing and