The hypothesis that S* is a vibrationally-excited ground-state population is tested and discarded for two carotenoid samples: beta-carotene in solution and rhodopin glucoside embedded in the light harvesting 2 protein from Rhodopseudomonas acidophila. By demonstrating that the transient absorption signals measured in both systems that are induced by broadband (1000 cm (1)) and narrowband (50 cm (1)) excitation pulses are near identical and hence bandwidth independent, the impulsive stimulated Raman scattering mechanism proposed as the primary source for S* generation is discarded. To support this conclusion, previously published multi-pulse pump-dump-probe signals [17] are revisited to discard secondary mechanisms for S* formation. (C) 2010 Elsevier B.V. All rights reserved.