Isotopic species, vibrational states and nuclear quadrupole splitting in CH2Cl2 from rotational spectroscopy at 8–18 GHz

The present work fills several significant gaps in the study of the rotational spectrum of the methylene chloride molecule. Two Fourier transform microwave spectrometers were used, providing complementary coverage of the 8–18 GHz region, at room temperature and in supersonic expansion. Hyperfine resolved measurements were made and fitted for ground states of the CH${}_2$³⁵Cl${}_2$, CH${}_2$³⁵Cl³⁷Cl, CH${}_2$³⁷Cl${}_2$, and ¹³CH${}_2$³⁵Cl${}_2$ isotopic species, as well as for nine different excited vibrational states. Transitions in the $v_4=2$, $v_4=3$, $v_3=1$, $v_9=1$ states in CH${}_2$³⁵Cl${}_2$, and transitions in excited states of the ${\nu }_4$ mode in ³⁵Cl³⁷Cl and ³⁷Cl${}_2$ isotopic species have been assigned for the first time. Vibrational and isotopic dependence of nuclear quadrupole coupling constants was identified. The $v_3=1$ and $v_9=1$ states in CH${}_2$³⁵Cl${}_2$ were found to be significantly coupled by $c$-axis Coriolis interaction, while transitions in $v_4=2$ and $v_4=3$ states exhibited hyperfine mediated perturbations enhancing the determination of the ${\chi }_{ab}$ parameter and allowing assessment of its vibrational dependence.