2001MNRAS.325..273X

We have searched for molecular absorption lines at millimetre wavelengths in 11 gravitational lens systems discovered in the JVAS/CLASS surveys of flat spectrum radio sources. Spectra of only one source 1030+074 were obtained in the 3-, 2- and 1.3-mm bands at the frequencies corresponding to common molecular transitions of CO and HCO⁺ as continuum emission was not found in any of the other sources. We calculated upper limits to the column density in molecular absorption for 1030+074, using an excitation temperature of 15K, to be N_CO<6.3x10¹³cm^–2 and N_HCO+<1.3x10¹¹cm^–2, equivalent to hydrogen column density of the order N_H<10¹⁸cm^–2, assuming standard molecular abundances. We also present the best upper limits of the continuum at the lower frequency for the other 10 gravitational lenses.