Ethenium has been observed in rarefied gases subjected to radiation. Another preparation method is to react certain proton donors such as trihydrogen cation|, helium hydride ion|, diazenylium|, and  with ethane at ambient temperature and pressures below 1 mmHg. (Other donors such as methanium| and  form ethanium preferably to ethenium.)
At room temperature and in a rarefied methane atmosphere, ethanium slowly dissociates to ethenium and . The reaction is much faster at 90 °C.