Evolution of the column density (N_LTE) as a function of the rotation temperature (T_rot) for the transitions of the molecular species observed in 2011 (Table A.1 and Eq. (4)). Each curve corresponds to a different transition and the dashed curves delimit the 1σ uncertainties. The curve intersections give the values of N_col and T_rot . The vertical dotted line indicates T_CMB = 5.14 K.