The homogeneous catalytic hydroformylation of 3,3-dimethylbut-1-ene was studied, starting with Rh-4(sigma-CO)(9)(mu-CO)(3) as catalyst. The multiple experiment in situ spectroscopic data were preconditioned to subtract the absorbance due to background moisture, carbon dioxide, and solvent. The preconditioned data were then subjected to band-target entropy minimization (BTEM) in order to recover the pure component spectra of the species present-using no libraries and no a priori information. The pure component spectra of the main species present, namely, the organic reactant 3,3-dimethylbut-1-ene, the organic product 4,4-dimethylpentanal, the catalyst precursor Rh-4(mu-CO)(9)(mu-CO)(3), and the observable organometallic intermediate RCORh(CO)(4), were all readily recovered. In addition, it was possible to recover the expected minor species, namely 2-methyl-3,3-dimethylbutanal, Rh6(CO)16, and a recently identified cluster Rh-4(sigma-CO)(12). The latter two species exist at ppm levels. The new BTEM algorithm shows that successful and detailed in situ spectroscopic system identification for catalytic studies is possible given no prior information.