• rotational energy transfer;
  • collisional dephasing;
  • spectral exchange;
  • rotational relaxation;
  • time-domain CARS


In this paper we present a comparative analysis of two alternative approaches to the description of the rotational energy transfer (RET) in the ‘blue’ (1388 cm−1) Q-branch of the CO2ν1/2ν2 Fermi dyad based on the simplified spectral exchange (SE) and rotational relaxation (RR) models. The analysis was carried out using a special approximation error minimization procedure for fitting the theoretical model to experimental impulse responses obtained by time-domain CARS at low and moderate densities. At densities ρ≥ 1 amagat, the collisional dephasing (CD) contribution to the linewidth substantially prevails over the width attributed to the rotational structure. The impulse response beating analysis and the fitting results clearly proved that in contrast to the ‘red’ (1285 cm−1) band, the SE model is more appropriate in comparison with the RR model for a description of the RET in the ‘blue’ Q-branch. Copyright © 2007 John Wiley & Sons, Ltd.