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The pure rotational spectrum of CCl2 in the ground state was observed for the first time in the millimeter‐ and submillimeter‐wave region. The CCl2 molecule was generated directly in a free space cell by a dc glow discharge in CCl4 . Several transitions showed hyperfine splittings arising from the nuclear quadrupole coupling of two Cl atoms. Analysis of the observed spectrum yielded the rotational, centrifugal distortion, and nuclear quadrupole coupling constants of the C35 Cl2 species. The r0 structure was derived from the rotational constants to be r0 (C–Cl)=1.7157 A and θ0 (ClCCl)=109.2°. The ionic and π character of the C–Cl bond were estimated from the nuclear quadrupole coupling constants to be 0.26 and 0.32, respectively.

The gas‐phase spectrum of BH3 was detected for the first time by diode laser spectroscopy through the observation of the ν2 band. The borane was produced by photolysis of B2H6 or BH3CO with an ArF excimer laser. The same spectrum was obtained by a discharge in a B2H6 and He mixture. Line assignments were made for the Q‐branch series with J=K of the ν2 band; effects due to Coriolis perturbations by the ν4 state were recognized.

A spectrum of a 2Π-2Σ transition has been observed in the wavenumber region 2088–2130 cm−1 by a discharge in an acetylene and hydrogen mixture and is assigned to the ν2 + ν3 combination band of CCH. The vibrational frequency of this band (2091 cm−1) is much lower than the sum 2212 cm−1 of the ν2 (370 cm−1) and ν3 (1841 cm−1) fundamental frequencies. This low frequency and a large change in the effective spin-orbit interaction constant from the v2 = 1 state are explained by a vibronic interaction between the A 2 Π and X 2 Σ states.

The pure rotational spectrum of the isotopically substituted methoxy radical 13CH3O was observed in the millimeter‐ and submillimeter‐wave region. The 12CH3O radical was also studied in the same wavelength region and the molecular parameters of the previous work were reexamined. It was found necessary to add a few terms for the centrifugal distortion. The hyperfine coupling constants of the carbon nucleus were determined for the first time. With reference to the rotational constants of CD3O, the rs structure of the methoxy radical was determined.