Detection of the propargyl radical at lambda 3mm

We thus included the measured frequencies in a new spectroscopic analysis to provide accurate frequency predictions for the interstellar search for propargyl at mm wavelengths. Moreover, we recommend that future searches for CH_2_CCH in cold interstellar clouds are carried out at lambda 3mm, rather than at lambda 8 mm. The 505-404 transition is about five times more intense than the 202-101 transition in TMC-1, which implies that detecting the former requires about seven times less telescope time than detecting the latter.

We constrain the rotational temperature of CH_2_CCH in TMC-1 to 9.9+/-1.5K, which indicates that the rotational levels of this species are thermalized at the gas kinetic temperature. The revised value of the column density of CH_2_CCH (including ortho and para species) is (1.0+/-0.2)x10^14^cm^-2^, and thus the CH_2_CCH/CH_3_CCH abundance ratio is revised from slightly below one to nearly one. This study opens the door for future detections of CH_2_CCH in other cold interstellar clouds, making possible to further investigate the role of this very abundant hydrocarbon radical in the synthesis of large organic molecules such as aromatic rings.