[en] The measurement of the carbon isotope abundances ratio in comets allows to constrain the conditions in the outer protosolar nebula. Different measurements of the 12C/13C ratio, using various molecules, have already been published for different solar system objects, such as the Sun, the Earth, the Moon, asteroids, planets or comets. So far all these measurements are consistent with 12C/13C' 90 but some significant differences have been seen. In comets this ratio is remarquably constant and equal to 91.0±3.6  for studies based on CN radical but present larger variations with studies based on other radicals . In this work we present a new analysis of this ratio, based on two different approachs for modeling the 12C2 and 12C13C emission spectrum and the (1,0) and (2,1) bandheads of 12C13C. Observational data obtained at high resolution (' 70, 000) using the 8.2-m Kueyen telescope (UT2) of the Very Large Telescope (VLT) with the Ultraviolet and Visual Echelle Spectrograph (UVES) instrument have been used to test our modeling and measure the 12C/13C ratio in two different comets: C/2001 Q4(NEAT) and C/2002 T7 (LINEAR). Our modeling and numerical results will be presented.