Anomalous absorption in rhomboidal SiC3 molecules

Laboratory detection of two isomers Of Cyclic SiC(3) molecule have been reported by McCarthy et al. (1999a, 1999b) and Apponi et al. (1999b). Seven transitions of the isomer-I have been detected in IRC+10216 by Apponi et al. (1999a). However, to date, the second isomer is not detected in the interstellar space. Here, we propose identification of isomer-I through the transition 4(22) - 4(23) at 0.2 GHz and of isomer-II through the transitions 2(20) - 2(21) at 4.44 GHz and 4(40) - 4(41) at 2.16 GHz, in absorption against the cosmic microwave background (CMB). In absence of the availability of the collisional rates, we have used scaled values for them. However, we have checked the sensitivity of the lines on the rates by enhancing the rates for transitions with Delta k(a) = 0 by a factor of 10 and the results are not found sensitive.