Existence of Acetaldehyde Clathrate Hydrate and Its Dissociation Leading to Cubic Ice under Ultrahigh Vacuum and Cryogenic Conditions

Acetaldehyde in a dilute aqueous solution gets hydratedto producea geminal diol under atmospheric conditions. The acetaldehyde-waterice system under high pressure also converts to a geminal diol, andtherefore, its stable clathrate hydrate (CH) phase, which in mostsystems forms at high pressures, is unknown. In the present study,we showed that acetaldehyde CH exists in ultrahigh vacuum (10(-10) mbar) under cryogenic conditions (below 140 K) andcontinues to exist at 115 K for periods well over 1 day. Decompositionof acetaldehyde CH at 130-135 K produces water ice in its cubiccrystalline form. The mechanism and kinetics involved in the processhave also been studied. Reflection absorption infrared spectroscopyand temperature-programmed desorption mass spectrometry were utilizedto confirm the CH formation. Our study establishes the possibilityof a stable CH phase for acetaldehyde in interstellar and cometaryenvironments.

Automated summary

Acetaldehyde in dilute solution can form geminal diol under normal atmospheric conditions. This study discovers the existence of stable acetaldehyde clathrate hydrate (CH) in ultrahigh vacuum at cryogenic temperatures. The formation of CH was confirmed using infrared spectroscopy and mass spectrometry. This finding suggests the possibility of stable CH phase for acetaldehyde in interstellar and cometary environments.