Cationic complex-enhanced C-H stimulated Raman scattering in naphthalene-benzene solution

Area of Science:

• Spectroscopy
• Plasma Physics
• Computational Chemistry

Background:

• Ring skeleton vibrations typically dominate aromatic Raman spectra over C-H stretching.
• Stimulated Raman scattering (SRS) is sensitive to molecular vibrations.

Purpose of the Study:

• Investigate the effect of laser-induced plasma (LIP) on SRS of aromatic C-H stretching vibrations.
• Understand the mechanism behind anomalous SRS enhancement in mixed aromatic solutions.

Main Methods:

• Generation of laser-induced plasma in mixed naphthalene-benzene solutions.
• Analysis of stimulated Raman scattering spectra.
• Density functional theory (DFT) calculations of molecular interactions and Raman activity.

Main Results:

• Anomalous enhancement of naphthalene's C-H stretching SRS (3055 cm⁻¹) was observed.
• SRS of benzene's C-H stretching vibrations (3060 cm⁻¹) disappeared in the mixture.
• DFT calculations revealed enhanced C-H Raman activity in (naphthalene-benzene)⁺ heterodimers.
• Self-focusing in pure benzene and naphthalene led to compressed SRS pulse durations.

Conclusions:

• Transient ionized species in LIP significantly enhance SRS of naphthalene's C-H vibrations.
• The formation of (naphthalene-benzene)⁺ heterodimers is key to the observed Raman activity enhancement.
• Self-focusing effects influence SRS pulse characteristics in pure aromatic compounds.