Infrared matrix isolation and ab initio studies on isothiocyanic acid HNCS and its complexes with nitrogen and xenon

Abstract

The isothiocyanic acid HNCS (DNCS) and its complexes with nitrogen and xenon have been studied experimentally by FTIR matrix isolation technique and computationally with the use of ab initio calculations at the MP2 level. The spectra show that HNCS (DNCS) interacts specifically with nitrogen forming 1:1 hydrogen bonded complex in argon matrix while non-hydrogen bonded structure is probably formed in solid xenon. Two stable minima were localized on the potential energy surface. One of them involves an almost linear hydrogen bond from NH group of the acid molecule to nitrogen molecule lone pair (structure I) and has an interaction energy ΔECP equal to −6.85 kJ/mol. The second structure (II) where the nitrogen molecule interacts with the sulfur atom of the HNCS was found to be weaker bound and is characterized by ΔECP=−1.99 kJ/mol. A low energetic barrier of 5.86 kJ/mol between the structures I and II was found. Both experimental and theoretical results obtained for the Xe⋯HNCS system point to a structure with the NH group interacting with the xenon atom. An interaction energy ΔECP for this complex is equal to −3.64 kJ/mol.