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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 v2 = 1←0, 2←1, and 3←2 bands of the methyl radical were observed in the gas phase by infrared tunable diode laser spectroscopy at 606.4531, 681.6369, and 731.0757 cm−1. The observed vibration–rotation spectra were analyzed to derive precise values for the rotational constants, centrifugal distortion constants, and spin–rotation interaction constants. The absence of N = odd, K = 0 levels in the v2 = even states and of N = even, K = 0 levels in the v2 = odd states was confirmed, indicating that each vibrational state is nondegenerate. The observed band origins, when analyzed, led to a potential function for the out‐of‐plane bending vibration that has no potential hump at the planar configuration. The large negative anharmonicity of this potential was ascribed to a vibronic interaction with excited electronic states. The methyl radical was generated by a 60 Hz discharge in di‐tert‐butyl peroxide and was found to have a lifetime of about 1.4 msec; its concentration in the absorption cell was estimated to ...

Rotational spectra of CH3CHD2 were observed by using a source‐modulation microwave spectrometer. Of 26 observed transitions, 16 showed splittings due to internal rotation. An analysis of the observed spectra, which utilized an internal axis method modified to include centrifugal distortion effects, gave the following results: A=60 809.592 (59) MHz, B=17 770.87 (16) MHz, C=17 084.84 (16) MHz, F=257.70 (35) GHz, and V3=2.8783 (28) kcal/mole, with 2.5 times standard errors in parentheses. In the analysis V6=0 was assumed, and D, a constant associated with a cross product of inertia, was fixed to a calculated value. When the uncertainty in D is taken into account, the error of V3 increases to 0.0029 kcal/mole. Effects of the molecular vibrations on the barrier are discussed briefly.

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.

The microwave spectrum of the trifluoromethyl radical in the ground 2A1 state has been observed by using a source frequency modulation spectrometer. The CF3 radical was generated directly in the absorption cell by a glow discharge in trifluoroacetic acid anhydride (CF3CO)2O. The observed transitions included N = 4 ← 3, 5 ← 4, and 6 ← 5, all of which are resolved into K as well as fine and hyperfine structure components. A magnetic hyperfine Hamiltonian was derived for three identical nuclei with a spin of 1/2 (the fluorine nuclei) in a doublet symmetric‐top molecule, in order to analyze the observed spectrum. Most of the hyperfine structure could be explained by considering the total nuclear spin operator I0 = JiIi, except for the K = 1 transitions; some of them were clearly resolved into doublets and the observed splittings allowed us to determine the additional dipole–dipole hyperfine interaction constant ‖ Taa−Tbb ‖. The rotational constant B0 was determined to be 10 900.9118(52) MHz, with 2.5 times th...

The microwave spectra of the HSO and DSO radicals in the ground state were observed in glow discharges in a mixture of H2S or D2S and O2. Both a‐type and b‐type transitions were assigned and analyzed. The hyperfine coupling constants of the hydrogen nucleus of HSO were determined for the first time. These constants resulted in a conclusion that the ground electronic state of HSO is 2A″. The rotational constants, centrifugal distortion constants, and spin–rotation coupling constants including their centrifugal distortion terms for both the species were also determined with good precision. The diagonal components of the magnetic hyperfine interaction for the deuterium nucleus of DSO were not obtained because most of the hyperfine splittings were not resolved or resolved partially. However, the off‐diagonal component Tab was determined from an analysis of a local perturbation between the 312 J = 7/2 and 404 J = 7/2 levels connected by the eab+eba term.

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.

The vibrational satellites of SF4 have been observed for the two lowest bending modes, ν4 and ν9. The relative intensities which were observed are consistent with the vibrational assignment of Frey et al. but are incompatible with Levin’s assignment. Consideration of the Coriolis interaction between the two modes lead to the same conclusion. The centrifugal distortion constants are evaluated and are compared with the observed.

The J = 3 ← 2, K−1 = 2 and J = 4 ← 3, K−1 = 2 and 3 transitions were observed for the allene‐1,1‐d2 molecule. The B = (B + C)/2 and (A−B)bp2 constants have been determined to be 7846.158 ± 0.01 MHz and 0.133 ± 0.005 MHz, respectively. The observed values of the two centrifugal distortion constants, DJ = 0.0024 ± 0.0005 MHz and DJK = 0.130 ± 0.005 MHz, were compared with the calculated to confirm the assignment of the weak spectra. The Stark effect of the J = 4 ← 3, K−1 = 3 transition was analyzed by comparing with computer‐simulated spectrum, leading to the dipole moment of 0.0031 ± 0.0003 D.

The microwave spectrum of arsenic trifluoride was observed in the excited states of all the normal vibrations. The rotational constant at the equilibrium state was determined, and the equilibrium As–F distance was calculated to be 1.7044 A assuming the FAsF angle to be 95°58′. The l-type doubling constant, q4, and the asymmetry parameter, η, of the As nuclear quadrupole coupling constant were determined in the v4=1 to be 10.24±0.02 MHz and −0.005±0.01, respectively.