The microwave spectrum of propyne is critically reviewed for information applicable to radioââ¬Âastronomy. Molecular data such as the derived rotational constants, centrifugal distortion parameters, hyperfine coupling constants, electric dipole moment, and molecular structure are tabulated. The observed rotational transitions are presented for the astronomically interesting isotopic forms and the lowest lying vibrational state of propyne. Calculated rotational transitions are presented for the ground vibrational state of 12CH3 12Cââ°Â¡ 12CH, 13CH3 12Cââ°Â¡ 12CH, 12CH3 13Cââ°Â¡ 12CH and 12CH3 12Cââ°Â¡ 13CH, and for the vibrationally excited state ý10 of 12CH3 12Cââ°Â¡ 12CH. © 1981, American Association of Physicists in Medicine. All rights reserved.