  In order to deepen in the knowledge of the vibrational properties of
2-dimensional MoS2 atomic layers, a complete and systematic Raman scattering
analysis has been performed using both bulk single crystal MoS2 samples and
atomically thin MoS2 layers. Raman spectra have been measured under
non-resonant and resonant conditions using seven different excitation
wavelengths from near-infrared (NIR) to ultraviolet (UV). These measurements
have allowed to observe and identify 41 peaks, among which 22 have not been
previously experimentally observed for this compound, characterizing the
existence of different resonant excitation conditions for the different
excitation wavelengths. This has also included the first analysis of resonant
Raman spectra that are achieved using UV excitation conditions. In addition,
the analysis of atomically thin MoS2 layers has corroborated the higher
potential of UV resonant Raman scattering measurements for the non destructive
assessment of 2 dimensional MoS2 samples. Analysis of the relative integral
intensity of the additional first and second order peaks measured under UV
resonant excitation conditions is proposed for the non destructive
characterization of the thickness of the layers, complementing previous studies
based on the changes of the peak frequencies.
