Dispersive Raman Mode of Layered Compound 2H-MoS₂ under the Resonant Condition

A frequency shift of a Raman peak is observed in 2H-MoS 2 , when the exciting laser frequency ω i is tuned across the A and B excitonic levels. The frequency shift decreases as ω i increases. It can be explained as due to a resonant two-phonon Raman process of the successive emission of a dispersive longitudinal quasi-acoustic phonon and a dispersionless E 1u 2 phonon both along the c axis. The translational exciton masses along the c axis are estimated to be (1.3 ±0.2) m 0 for the 1 s state of the A exciton and (1.6 ±0.3) m 0 for the 1 s state of the B exciton. The observed Raman cross section is consistent with qualitative estimation in terms of this Raman process.