From sublimation to tautomerization and aggregation: Infrared spectroscopic insights into ammonium thiocyanate dissociation at low temperatures

Abstract

The dissociation of ammonium thiocyanate (NH₄SCN) during the sublimation of NH₄SCN to form isothiocyanic acid (HNCS; a tautomer of HSCN) and ammonia (NH₃) was evidenced by matrix isolation infrared spectroscopy. HNCS was observed to behave differently within Ar and N₂, on annealing the matrices. Formation of homodimers of HNCS is notably more rapid in N₂ than in Ar. Interestingly, the infrared spectra of solid film of NH₄SCN at 10 K obtained by refreezing sublimed NH₄SCN did not show any characteristic dissociation. Experimental results were corroborated with the computations performed at B3LYP-GD3/aug-cc-pVDZ level.