The microwave spectrum of dichlorine oxide. Molecular structure, centrifugal distortion coefficients, and force field

Abstract

The microwave spectra of the three chlorine isotopic species (35/35, 35/37, 37/37) of dichlorine monoxide have been measured in the region 9–40 Gc./sec. Rotational constants and centrifugal distortion constants have been obtained and used to calculate the structural parameters and the harmonic force constants of the molecule.

The structure is highly over-determined. The mean values of the nine r_o structures are d= 1·70038 ± 0·00069 Å for the bond length, and α= 110·96 ± 0·08° for the bond angle. The mean values of the nine r_s structures are d= 1·70038 ± 0·00043 Å and α= 110·86 = 0·04°. For ³⁵Cl₂O the centrifugal distortion constants could be obtained with sufficient accuracy to allow the determination of all force constants of the general harmonic force field: f_d=(2·88 ± 0·08)× 10⁵, f_dd=(0·31 ± 0·05)× 10⁵f_α/d²=(0·432 ± 0·002)× 10⁵, and f_dα/d=(0·17 ± 0·01)× 10⁵(all in dyne/cm.). The force constants are compared with those evaluated by conventional procedures from infrared-spectral data, and it is found that the molecular vibrational frequencies calculated from the force field evaluated solely from microwave data agree well with those observed. The results support the view that centrifugal distortion coefficients for asymmetric rotors provide a useful source of information about molecular force fields. Attention is drawn to the importance of data selection in the evaluation of centrifugal distortion constants.