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

Ring skeleton vibrations of aromatic series are dominant in Raman spectroscopy compared with the C-H stretching vibrations. When a laser-induced plasma (LIP) was generated in a mixed solution of naphthalene and benzene, an anomalous enhancement was observed in stimulated Raman scattering (SRS) of aromatic C-H stretching vibrations of naphthalene (3055 cm-1). However, SRS of C-H stretching vibrations of benzene at 3060 cm-1 disappeared. The LIP produced electrons and cations, and the transient production of ionized material contributed to the enhancement of SRS of C-H vibrations of naphthalene. Density functional theory calculations showed that the C-H Raman activity of the naphthalene molecules in (naphthalene-benzene)+ heterodimer was significantly enhanced compared with neutral naphthalene. In addition, SRS pulse durations were better compressed in pure benzene and naphthalene due to the self-focusing effect.