  Broadening of the Raman scattering (RS) spectra was studied in monolayer
graphene samples irradiated with various dose of ions followed by annealing of
radiation damage at different temperatures. It is shown that the width {\Gamma}
(full width at half maximum, FWHM) of three main RS lines (G-, D-, and 2D)
increases linearly with increase of the density of irradiation-induced point
defects N d as {\Delta}{\Gamma} = m N d . The slope m of the linear
dependencies is the same for one-phonon emitting G-line and D-line, and almost
double for two-phonon emitting 2D-line. It is also shown that the width of
D-line {\Gamma} D for all samples is larger than one half of the width of
2D-line {\Gamma} 2D , which shows that in the case of D-line, elastic electron
scattering on point defects leads to an additional decreasing the lifetime of
the emitted phonon. Theoretical model of the width of D-line in disordered
graphene is developed which explains the experimental observations and allows
to determine the numerical coefficient in the in-plane transverse optic phonon
dispersion in graphene.
