Coherent Anti-Stokes Raman Spectroscopy of Polycyclic Aromatic Hydrocarbons

Abstract

Coherent anti-Stokes Raman spectroscopy (CARS) was used to obtain Raman spectra of thirteen polycyclic aromatic hydrocarbons (PAHs) composed of between three and seven fused rings. The compounds were pumped in the resonance and preresonance regions to obtain the sensitivity necessary for examination at concentrations down to 1.5 × 10 −5 M. A simple mixture of three PAHs was optically separated through the wavelength selectivity of the resonant enhancement process. Comparisons between the spectra of the mixture and the spectrum of each pure component showed essentially no differences when pumped at the same wavelength. Finally, lineshape analysis was performed on the CARS spectra to facilitate comparisons between classes of compounds and for quantitative purposes.

Analytic ab initio calculations of coherent anti-Stokes Raman scattering (CARS)

“…It is worth mentioning that tetracene as well as 1,2-benzanthracene needed special experimental procedures in order to obtain high-quality spectra, as reported in ref. 54 and 55, which might have affected the appearance of the final spectra, making a direct comparison with our results difficult.…”

“…As discussed in ref. 54, the character of the spectra can change when different concentrations of the sample are used, whereas the reconstructed spectra obtained from two spectra recorded for different concentrations of the substance were found to be nearly identical.…”

“…The corresponding experimental spectra obtained in tetrahydrofurane solution have been reported in ref. 54 and 55 for pump wavelengths in the range 365-480 nm, corresponding to the frequency range 0.0949-0.1248 a.u. The calculated CARS spectra, plotted in the fingerprint region for fused rings (1000-1800 cm À1 ), are reported in Fig.…”

Resonance CARS line shape analysis for a concentration series of a dye solution—a practicable method for the evaluation of third‐order susceptibilities

“…Its value can be better determined by a leastsquares fit ofthe spectral function (2) to the experimental line shape over a spectral region which is formed by the Raman line concerned.…”

Raman spectroscopy

“…CARS has also been used in the study of excited states of metalloporphyrins (392), of polycyclic aromatic hydrocarbons (393), of commercial oil samples (394), and of radical reactions (395). Coal gasification streams have been analyzed (396), and surface-enhanced CARS has been observed when the active molecules are located near the surface of a small silver particle (397).…”