Vibration-rotation spectra and molecular force field of methylene fluoride and methylene fluoride-d 2

Infrared spectra of CH ₂F ₂ and CD ₂F ₂ have been measured under a medium resolution. The vibration-rotation bands of CD ₂F ₂ fundamentals have been analyzed and the assignment for the fundamentals of CD ₂F ₂ is given. In addition, a number of overtone and combination bands are observed for CH ₂F ₂, which helps to clarify the vibrational assignment for CH ₂F ₂. A normal coordinate treatment has been carried out: The force constants in a modified Urey-Bradley as well as the general valence force fields have been determined, the vibrational frequencies and the centrifugal distortion constants obtained from microwave spectroscopy being used. The force constants of the methylene fluoride molecule are discussed in connection with those of the related molecules. Special features of the CH ₂F ₂ and CD ₂F ₂ spectra are also described.