CO molecules in the shells of quasars 1556+3517 and 0840+3633

New class of low- ionization BAL quasars (Becker et al. 1997), represented by QSO 1556+3517, 0840+3633 and 0059-2735, is considered. Their optical spectra are completely dominated by absorption features, whereas emission lines are weak or absent. Possibility to explain these exclusive features of their spectra by existence of molecular shells, responsible for the absorption is discussed. In particular, it is suggested to identify line at lambda = 2063 A, attributed to CrII, as a line of Cameron band of CO molecule. Estimation of the expected optical depth value in rotational radio lines of this molecule is made. It is suggested to carry out radio observations of quasars 1556+3517 and 0840+3633 to check the molecular hypotheses.