A TEST OF DIFFERENT ROTATIONAL RAMAN LINEWIDTH MODELS - ACCURACY OF ROTATIONAL COHERENT ANTI-STOKES-RAMAN SCATTERING THERMOMETRY IN NITROGEN FROM 295-K TO 1850-K

Rotational Raman linewidths calculated from three different models hav e been used in temperature measurements by rotational coherent anti-St okes Raman scattering (CARS)-a semiclassical ab initio model, the modi fied exponential energy gap model (MEG), and the energy corrected sudd en scaling law (ECS). Experimental rotational CARS spectra were genera ted, using the dual-broadband approach, in pure nitrogen at atmospheri c pressure in a heat pipe in the temperature range from 295 to 1850 K. Below 1500 K, the temperatures evaluated using the ECS linewidths agr eed with the heat-pipe temperatures to within 20 K. Above 1500 K, the errors in the evaluated temperatures increased steeply for all linewid th models, reaching errors of several hundreds of Kelvins at 1850 K. T his behavior of the evaluated temperature is probably caused by the un certainty in the values of the rotational Raman linewidths for high ro tational states at high temperatures. This work therefore illustrates that rotational CARS can be used for experimentally studying Raman lin ewidths and in particular their dependence on temperature and rotation al quantum number. The influence of different experimental parameters on the evaluated temperatures is discussed, and the spectral synthesis program is presented.