CN and CCH derivatives of ethylene and ethane: Confirmation of the detection of CH_3CH_2CCH in TMC-1

We present a study of CH_3CH_2CCH, CH_3CH_2CN, CH_2CHCCH, and CH_2CHCN in TMC-1 using the QUIJOTE^1 line survey. We confirm the presence of CH_3CH_2CCH in TMC-1, which was previously reported as tentative by our group. From a detailed study of the ethynyl and cyanide derivatives of CH_2CH_2 and CH_3CH_3 in TMC-1, we found that the CH_2CHCCH/CH_2CHCN and CH_3CH_2CCH/CH_3CH_2CN abundance ratios are 1.5±0.1 and 4.8±0.5, respectively. The derived CH_2CHCCH/CH_3CH_2CCH abundance ratio is 15.3±0.8, and that of CH_2CHCN over CH_3CH_2CN is 48±5. All the single substituted isotopologs of vinyl cyanide have been detected, and we found that the first and second carbon substitutions in CH_2CHCN provide a ^12C/^13C ratio in line with that found for other three-carbon bearing species such as HCCNC and HNCCC. However, the third ^13C isotopolog, CH_2CH^13CN, presents an increase in its abundance similar to that found for HCCCN. Finally, we observed eight b-type transitions of CH_2CHCN, and we find that their intensity cannot be fitted adopting the dipole moment μ_b derived previously. These transitions involve the same rotational levels as those of the a-type transitions. From their intensity, we obtain μ_b=0.80±0.03 D, which is found to be in between earlier values derived in the laboratory using intensity measurements or the Stark effect. Our chemical model indicates that the abundances of CH_3CH_2CCH, CH_3CH_2CN, CH_2CHCCH, and CH_2CHCN observed in TMC-1 can be explained in terms of gas-phase reactions.