Hyperfine structures of 2-cyanothiophene and 3-cyanothiophene: A quantum chemical study

A sufficient amount of spectroscopic data for S-substituted heterocyclic molecules are not available in the literature to adequately examine interstellar sulfur depletion. A quantum chemical investigation of quadrupole hyperfine structures of 2CNT, 3CNT, and some of their isotopologues is undertaken here in order to supplement the literature and supply new data that are valuable for the detection of new species in the ISM. The nuclear hyperfine quadrupole structures of 2-cyanothiophene (2CNT), 3-cyanothiophene (3CNT), and their ${}^{33}$S, ${}^{2}H$-isotopologues were analyzed at temperatures prevailing in regions where these compounds are expected to be found ($T\sim 5K$ to $T\sim 150$). The geometrical parameters were calculated using density functional theory (M06-2X/6-31G(d,p)) with empirical corrections for systematic errors. The ${}^{14}$N, ${}^{33}$S, and ${}^2$H quadrupole hyperfine constants, and dipole moments for 2CNT, 3CNT, ${}^{33}$S-2C¹⁵NT, ${}^{33}$S-3C¹⁵NT, 2C¹⁵NT-3D, and 2C¹⁵NT-2D were calculated, and their corresponding hyperfine structures were analyzed. The strongest transition lines and optimal regions of detectability were also discussed.