Transition metal dichalcogenides (TMDs) attract much attention due to their useful technological applications, including energy harvesting. Raman spectroscopy is a powerful technique for characterizing and extracting information regarding the electronic, vibrational and thermal properties of TMDs. We discuss a semi-ab-inito theoretical method  for calculating Raman linewidths in the transition metal dichalcogenides MoS2, WS2 and MoTe2 in their 2H bulk and monolayer structures. We present results for the temperature variation (in the range 50 - 1000 K) of the ratio of the widths of other Raman peaks with that of the A1g peak in bulk samples and with that of the A' peak in the monolayer samples. Our results indicate differing behaviours for MoS2, WS2 and MoTe2. These behaviours will be explained by analysing the roles of anharmonic and isotopic interactions of phonons in determining the linewidths in both the bulk and monolayer systems. Our calculated results for the linewidths of the A1g and E'2g modes in bulk MoS2 are in good agreement with measurements for pristine samples reported in [2,3]. However, our calculated values of the linewidths for the A' and E' modes in monolayer MoS2 are lower than experimental measurements [2,3,4]. An explanation of the discrepancy between our theoretical results and experimental measurements for all the six systems [2-6] will be attempted.
 I.O. Thomas and G. P. Srivastava, Submitted for publication.
 H. Guo et al, Appl. Phys. A 122, 375 (2016).
 K. Golasa et al, Acta Polonica A 124, 849 (2013).
 S. Mignuzzi et al, Phys. Rev. B 91, 195411 (2015).
 A. Berkdemir et al, Sci. Rep. 3, 1755 (2013).
 M. Yamamoto et al, ACS Nano 8, 3895 (2014).