“…The observed consistency of linewidth data for pure rotational and rovibrational transitions allows the conclusion that line broadening of the rovibrational line is predominantly governed by rotational relaxation phenomena involving rates due to collision-induced transitions between rotational levels which are not much dependent on the vibrational state. In contrast to this behavior, the lineshift data for the observed pure rotational transition (see Table 1) differ significantly from the corresponding values for the R-branch m = 5 transition of the fundamental vibrational band, determined to −82(10) kHz/Torr for CO-CO (17), −72.8 kHz/ Torr for CO-N 2 (32), and −84.9 kHz/Torr for CO-O 2 (33), respectively. Such differences are related to the fact that the rovibrational lines are predominantly shifted due to the isotropic part of the shifting cross section which does not contribute to the shifts of pure rotational transitions (36).…”