R.Wellington Davis

The microwave spectrum, centrifugal distortion constants, harmonic force field, and structure of dibromomethane

Abstract The microwave spectra of four isotopic species of dibromomethane have been measured up to J values ranging from 67 to 89 in the 12- to 74-GHz frequency region. These data have been combined with earlier measurements of lower J transitions by Chadwick and Millen [ Trans. Faraday Soc. 67 , 1539–1550 (1971)] and fit to yield values for rotational constants and centrifugal distortion constants. The quartic distortion constants have been combined with existing vibrational data to determine a harmonic force field for dibromomethane. The force constants and the rotational constants have been used to calculate a ground-state average structure and an approximate equilibrium structure for the molecule.

The microwave spectrum of the chain isomer of disulfur difluoride: FS-SF

Abstract The microwave spectra of two isotopic species of the chain isomer of disulfur difluoride, FS-SF, have been observed in the 15 to 80 GHz frequency range. For the F32S-32SF and F32S-34SF species respectively transitions with J values up to 84 and 50 were measured. These data have been analyzed together with some low J transition frequencies reported previously by R. L. Kuczkowski [J. Amer. Chem. Soc. 86, 3617–3621 (1964)] to yield values for the rotational constants and, for the first time, centrifugal distortion constants. The precisely determined quartic centrifugal distortion constants have been used together with vibrational wavenumbers for two isotopic species to obtain an improved harmonic force field for the FS-SF molecule. Effective, zero-point average and approximate equilibrium structural parameters have been calculated.

The molecular structures and harmonic force fileds of SO2, S2O, and S2O2 from combined spectroscopic and SCF results

A systematic study of the structure and force fields of the molecules SO2S2O and S2O2 has been made using a combination of results from SCF calculations and microwave and infrared spectroscopy. It has been possible to arrive at equilibrium structures for these three molecules through zero-point average geometries. A general harmonic force field for S2O2 is reported which accounts for the observed microwave spectroscopic data, and predicts the cis isomer of the molecule to have five observable infrared fundamentals.

The microwave spectrum of the pyramidal isomer of disulfur difluoride: SSF2

Abstract The pyramidal isomer of disulfur difluoride, SSF2, has been prepared by passing gaseous disulfur dichloride through heated potassium fluoride. The microwave spectra of three isotopic species of SSF2 have been measured in the 26- to 76-GHz frequency region. For the most abundant isotopic species transitions with J values up to 79 have been observed. These data have been combined with previous measurements of low-J lines by R. L. Kuczkowski [J. Amer. Chem. Soc. 86, 3617–3621 (1964)] and fit to obtain values for the rotational constants and centrifugal distortion constants. The quartic centrifugal distortion constants have been used together with existing vibrational data to determine an harmonic force field for the molecule. Finally, ground state average and equilibrium structures have been calculated for SSF2.

The microwave spectrum of oxygen-18-labeled phosphoryl chloride: Refinement of the harmonic force field and the molecular structure

Abstract The pure rotational spectra of 18OP35Cl3, 18OP35Cl237Cl, and 18OP37Cl3 have been measured for the first time, and the rotational spectrum of 16OP35Cl3 has been reinvestigated in the frequency range 30–80 GHz. Our experimental data have been analyzed to obtain values for rotational constants and a partial set of quartic centrifugal distortion constants for each species. These results have been combined with those of earlier microwave and vibrational studies to obtain an improved harmonic force field for phosphoryl chloride. The results of the present investigation have made it possible to determine for the first time a precise spectroscopic geometry for the OPCl3 molecule. Ground state effective, ground state average, and an approximate equilibrium geometry have been calculated. The ground state average geometry has been determined to be r z (OP) = 1.4464(6) A , r z (PCl) = 1.9929(2) A , and

Laser Stark spectroscopy of 1,1 difluoroethylene at λ=337 μm

Abstract Laser Stark spectra are given for 1,1 difluoroethylene (H 2 CCF 2 ) using laser λ = 337 μm. Three families of resonances are analyzed, two of them being the related transitions J ( K a , K c ) = 47(40, 8) ← 46(40, 7) and 47(40, 7) ← 46(40, 6). Relationships between the two transitions permit the calculation of both the zero-field transition frequencies and the effective dipole moment. A third family is assigned as 38(32, 7) ← 37(30, 8). The Stark shift is quasi-linear with E field, dominated by near-degenerate doublet interactions. Extended measurements and a reanalysis of the microwave spectrum are reported, in connection with the analysis of the far infrared spectrum.

The microwave spectrum, electric dipole moment, and nitrogen nuclear quadrupole coupling constants of 2-fluoropyrimidine

Abstract The microwave spectrum of 2-bromopyrimidine has been observed for the first time. For both the 79 Br and 81 Br isotopomers, R -branch transitions with J values ranging from 20 to 37 have been measured in the 38–75 GHz frequency range. Ground state rotational constants and values for four quartic distortion constants have been determined for both isotopomers. Hyperfine structure due to the presence of the quadrupolar bromine nucleus has been analyzed, yielding principal values of the quadrupole tensor as χ aa = 567.8(7), χ bb = −329(5), and χ cc = −239(5) MHz for the 79 Br isotopomer and χ aa = 475.6(6), χ bb = −274(2), and χ cc = −201(2) MHz for 81 Br. Our results demonstrate that the 2-bromopyrimidine molecule is planar and has C 2 V symmetry. The dipole moment of the molecule has been determined from Stark effect measurements to be 3.71(8) D.