Search for 111–110 and 211–212 transitions of H2CCO, H2CCC and H2CCCC in cosmic objects

Formaldehyde (H2CO) is the first molecule observed in absorption against the cosmic microwave background (CMB) through its transition 111–110 at 4.829 GHz in several cosmic objects. The second line observed in a large number of cosmic objects is 211–220 transition at 21.59 GHz of cyclopropenylidene (c-C3H2) in absorption against the CMB. The phenomenon of anomalous absorption can take place under rather peculiar conditions developed in a molecule generating the line. In the present investigation, for H2CCO, H2CCC and H2CCCC in cool cosmic objects, we have accounted for kinetic temperature of 10, 20, 30 and 40 K. For each of these three molecules, we have taken 30 rotational energy levels connected by 66 radiative transitions and solved the set of statistical equilibrium equations coupled with equations of radiative transfer through iterative method. We found that relative values of collisional rates can produce anomalous absorption of transitions 111–110 and 211–212 in these molecules. Anomalous absorption of 111–110 and 211–212 transitions may help in the identification of molecules in cool cosmic objects.