Detection of the linear SiC

We detected the linear 3Σ− radicals SiC3 and SiC5 toward IRC+10216 using an ultrasensitive line survey gathered with the Yebes 40 m radio telescope. The derived column densities of l-SiC3 and l-SiC5 are (3.6 ± 0.4) × 1012 cm−2 and (1.8 ± 0.2) × 1012 cm−2, respectively. The linear SiC3 radical is ∼2 times less abundant that its singlet rhomboidal prolate isomer, for which we provide a new analysis based on recent sensitive observations in the Q band (7 mm), and at 3 and 2 mm with the IRAM 30 m telescope. The emission detected from these species arises from the cool external layers of the circumstellar envelope. We speculate whether ion-neutral routes involving SiCnHm+ cations or neutral-neutral reactions involving Si and SiC2 could efficiently synthesize these species.