Rotational Spectra and Astronomical Search of Five Ethynyl Derivatives of Propene

The interstellar discovery of the five cyano derivatives of propene brings interest in analogous molecules that could be detected in similar astronomical environments. In this context, ethynyl-propene derivatives are good candidates to be observed in the Taurus Molecular Cloud (TMC-1), where other cyano and ethynyl derivatives of hydrocarbons such as ethane, allene, propene, and cyclopentadiene, among others, have been detected. We have investigated the pure rotational spectra of the five ethynyl-propene derivatives to enable their interstellar detections. These molecular species have been produced by an electric discharge and their rotational spectra were characterized using a Balle-Flygare narrow band-type Fourier-transform microwave spectrometer operating in the frequency region of 4-40 GHz. The spectral analysis allowed us to derive accurate spectroscopic parameters to obtain reliable frequency predictions for astronomical searches. We do not detect any of these species in TMC-1 but we derive upper limits for the abundances for the five isomers.