Microwave spectral studies of 2,4-difluorobenzaldehyde: O-trans conformer

The ground state microwave rotational spectra of 2,4-difluorobenzaldehyde (2,4-DFBD) vapor have been investigated in the frequency range 18.0–37.0 GHz using conventional microwave as well as Radiofrequency-Microwave Double Resonance (RFMWDR) spectroscopic techniques. A least-squares analysis of 50 a-type R-branch lines provides a set of rotational and centrifugal distortion constants which corresponds to the O-trans conformer of the molecule. The rotational constants are: A = 2498.977 (39) MHz, B = 958.043 (2) MHz and C = 692.394 (2) MHz. Detailed DFT calculations were carried out with various functional and basis sets to evaluate the spectroscopic constants, dipole moment and various structural parameters of the O-trans conformer of 2,4-DFBD for the ground state. It was found that the optimized geometry with B3LYP/6-311++g(2d,2p) basis set shows good agreement with the experimental values of the rotational constants.