What is the lowest energy structure of the NS2 molecule ?

A paramagnetic (neutral) species, thought to be the NS2 molecule, has recently been detected by Amano using millimeter wave spectroscopy in a discharge of a mixture of N2 and CS2. Detailed theoretical studies on the possible structures of an NS2 molecule, however, had not previously been reported. This study aims to find the most probable structure for the NS2 molecule and to characterize other conceivable isomers. Among many possible structures for the NS2 species, SNS bent (2A1), SNS linear (2Πu), NS2 ring (2B1), NSS bent (2A′), and SNS bent (4A2) isomers have been investigated at the self-consistent-field (SCF) and single and double excitation configuration interaction (CISD) levels of theory with double zeta plus polarization (DZ+P) and triple zeta plus double polarization (TZ+2P) basis sets. The SNS bent (2A1) isomer has been found to be the lowest energy structure among the isomers studied in this research. This bent isomer has a bond angle of about 150 deg and has a shallow double-minimum potential, the classical barrier height to linearity being 2.5 (3.0) kcal/mol at the TZ+2P-CISD(Q) level of theory.