The rotational spectroscopy of dichloromethane (CH235Cl2) in the ground state and ν4 vibrationally excited state from 11 to 750 GHz

The rotational spectrum of dichloromethane (methylene chloride, CH2Cl2) was measured with near-continuous frequency coverage from 29 to 750 GHz with 50 kHz resolution, with additional transitions around 11 GHz with 20 kHz resolution. The rest frequencies of transitions for both the vibrational ground state and first fundamental ν4 are observed, measured, and least-squares fit. Transitions for both of these vibrational states are modeled with partial octic, distorted rotor A- and S-reduced Hamiltonians in the Ir representation with nuclear quadrupole coupling. Computed spectroscopic constants at the B3LYP/6–311+G(2d,p) level are compared to their corresponding experimental values. The partition function of dichloromethane is updated.