April 2004

Isocyanic Acid

The detection of isocyanic acid (HNCO) in the interstellar medium was first reported in 1972 by Lew Snyder and David Buhl. It has since been observed in extragalatic sources. In comets, it was first observed in Hyakutake and then in Hale-Bopp.

HNCO has a dipole moment comparable to that of water. It is a strong organic acid with a pKa value of about 3.5. As such, it can lose a proton in an aqueous environment under certain conditions, particularly if a strong base is present. In this case, OCN- is formed.

HNCO is the smallest molecule containing the four dominant biogenic elements. A less stable isomer, cyanic acid (HOCN), has not been detected in the interstellar medium to date.

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