Rotational conformers and nuclear spin isomers of carbonyl diisothiocyanate

Nuclear spin isomers of molecules play a pivotal role in our understanding of quantum mechanics and can have significant implications for various fields. In this work, we report the isolation and characterization of stable nuclear spin isomers as well as conformational isomers of a reactive compound, namely carbonyl diisothiocyanate. It can exist as three rotational conformers, two of which, the syn-syn and syn-anti, were observed in a pulsed supersonic jet by chirped pulse Fourier transform microwave spectroscopy in the 2-12 GHz frequency region. The rotational spectra of two distinct nuclear spin isomers of syn-syn-carbonyl diisothiocyanate, ortho and para, were recorded and analyzed. Experimental molecular rotational parameters for the identified rotational and nuclear spin isomers were determined, including rotational constants, centrifugal distortion constants, and nuclear quadrupole coupling constants. The two nuclear spin isomers are distinguished by unique hyperfine splitting signatures in their rotational spectra as an outcome of their different nuclear spin states. The relative abundances of the two observed conformers in the gas phase were estimated from the intensity of their rotational transitions. Following detection of singly substituted rare isotopologues of the syn-syn conformer, a partial substitution (r_s) structure was determined.