Microwave spectrum of the FS2 radical in the ground electronic X̃ 2A″ state

The microwave spectrum of the CH2CP radical in its 2B1 ground electronic state was detected for the first time using a source-modulated microwave spectrometer. The radical was generated in the cell by a dc-glow discharge in a mixture of PH3 and C2H2. Fine structure was observed but no hyperfine structure pertaining to the phosphorus and hydrogen nuclei could be resolved. In total 110 spectral lines were measured for the K-structure and fine structure of eight rotational transitions in the 300–380 GHz region. The rotational, centrifugal distortion, and spin-rotation coupling constants were obtained by a least-squares analysis of the measured frequencies. On the basis of accompanying coupled cluster calculations an accurate equilibrium structure could be established; re(CH)=1.0816(5) Å, αe(HCH)=118.22(5)°, R1e(CC)=1.3418(10) Å, and R2e(CP)=1.5889(10) Å. The equilibrium dipole moment is predicted to be μe=−1.15 D, with the negative end at the phosphorus site.

The microwave spectrum of the most abundant isotopic species of the boron monosulfide radical 11B32S in the ground electronic state X 2Σ+ has been observed with a glow discharge cell spectrometer. Boron monosulfide was produced in an absorption cell by a glow discharge through a gaseous mixture of boron trichloride and hydrogen sulfide. The transitions were observed for N=2–1 to N=7–6 which fell in the frequency region up to 332 GHz. The molecular parameters were derived by a least-squares analysis: these included the rotational and centrifugal distortion constants, the spin–rotation interaction constant, the magnetic hyperfine interaction constants, and the nuclear quadrupole interaction constant. The nuclear spin-rotation interaction constant was also determined.

The rotational spectrum of the ClS2 free radical in the gaseous phase has been observed in the millimetre- and submillimetre-wave regions. The ClS2 radical was generated by a dc glow discharge in either S2Cl2 or SCl2. Both a- and b-type R-branch transitions, most of which were split into two fine structure components, were detected for both of the 35Cl and 37Cl isotopic species in the ground vibronic state. As expected from the small hyperfine interaction constants reported by an electron spin resonance (ESR) study, the hyperfine structure was resolved for none of the transitions observed in the present study. Analysis of the observed transition frequencies yielded rotational and centrifugal distortion constants and also spin–rotation interaction constants with their centrifugal corrections. The spin–rotation interaction constants obtained in the present study were consistent with g values of the ESR study. The rotational constants of the two isotopic species led to the structure parameters r(S—S) = 1.906 (7) Å, r(S—Cl) = 2.071 (5) Å, and θ(SSCl) = 110.3 (4)°. A harmonic force field was derived from the observed centrifugal distortion constants and inertial defects combined with the ν1 frequency reported in literature on electronic spectroscopy. This harmonic force field yielded the ν2 and ν3 frequencies (445 (21) and 213.0 (2) cm−1, respectively, for 35ClS2), which differed considerably from the values reported previously.

U 2-centers in alkali halides are neutral hydrogen atoms in interstitial lattice sites, as has been shown by EPR measurements. The hyperfine interactions with the proton and with the four nearest halogen nuclei are resolved in the EPR spectrum. In order to resolve hyperfine interactions with further nuclei of the surrounding lattice ENDOR measurements have been performed onU 2-centers in KCl at 77 °K. The analysis of the ENDOR spectra gave precise values for the hyperfine and quadrupole interaction constants of the nearest neighbour chlorine and potassium nuclei. The isotropic hyperfine constant of the chlorine neighbours is 24 times larger than that of the potassium neighbours although both nuclei are on equivalent first shell lattice positions. The hyperfine interactions of second shell potassium nuclei [(1/2, 1/2, 3/2)-position] show an unexpectedly large isotropic hyperfine constant. One expects a pure magnetic dipole-dipole interaction for the outer shell nuclei because of the concentrated hydrogen wave function. Two further chlorine shells could be approximately analysed. A theoretical estimate of the hyperfine and quadrupole interaction constants was made by orthogonalizing the 1s hydrogen wave function to the cores of the surrounding ions. If one takes into account the mutual overlap of neighbouring potassium and chlorine ions, one gets the right order of magnitude of the measured constants and a value of 10.4∶1 for the ratio of the isotropic hyperfine constants of the first shell chlorine and potassium nuclei. The relatively large isotropic constant of the second shell potassium nuclei can also be explained on this basis.

The pure rotational transition of the NF radical in the second electronically excited state, b 1Σ+, was detected by microwave spectroscopy. The NF radical was generated by dc-discharge through a mixture of NF3 and H2 at around 90 K. Six rotational transitions for v=0 and four for v=1 were observed in the 73–442 GHz region. In addition to the rotational and centrifugal distortion constants, the quadrupole coupling constant of the nitrogen nucleus of NF(b 1Σ+) was determined for the first time from the lowest two transitions of NF in the v=0 level. The spectrum of NF(a 1Δ) in the first vibrational excited state was also observed in order to derive highly accurate potential parameters for comparison with the data of NF(X 3Σ−,b 1Σ+).

Microwave spectrum of nitroxyl

A microwave investigation from 25–165 GHz has been made of the ground state rotational transitions of OC79Br2, OC79Br81Br and OC81Br2. The r0 structure gives the CO distance as 117.2 pm, the C–Br distance as 191.7 pm and the BrCBr angle as 112.3°, and the C2v structure is fully confirmed. Centrifugal distortion constants and quadrupole coupling information were obtained and a force-field consistent with the centrifugal distortion and the known vibration frequencies is evaluated.

Internal rotation and structure of thiophenol and 4-fluorothiophenol studied by microwave spectroscopy and quantum chemistry

The microwave spectrum and structure of chloryl fluoride

A simple carbene, the HCCN radical, has been identified in the gas phase using a microwave spectroscopic method. The HCCN molecule was generated in a free space absorption cell by the reaction of CH3CN with the microwave discharge products of CF4. Five rotational transitions, each split into three fine structure components, were observed in the region of 110 to 198 GHz. No hyperfine structure was resolved, although some of the observed lines showed broadening. The rotational constant, the centrifugal distortion constant, the spin–spin coupling constant, and the spin-rotation coupling constant were determined with good precision. The observed spectrum is completely consistent with that expected for a linear molecule in a 3Σ state, in agreement with an earlier matrix EPR study of Bernheim et al. [J. Chem. Phys. 43, 196 (1965)].

Pulsed electron−nuclear double resonance and electron spin−echo envelope modulation spectroscopies have been used to characterize the bis(phenyl isocyanide) complexes of iron(III)-tetraphenylporphyrin ([TPPFe(PhNC)2]+) and iron(III)-octaethylporphyrin ([OEPFe(PhNC)2]+) that have the dxy orbital configuration. The spin density distribution in the porphyrin π system was obtained, with major spin density (∼0.06) being delocalized to each meso carbon atom. The spin density on the pyrrole β carbons was found to be negligible. The upper limit for spin density on Fe3+ was estimated to be about 0.63. The hyperfine interaction constants on the pyrrole nitrogens (on average, ∼3.3 MHz) were also evaluated. The overall spin density distribution obtained was found to be in agreement with that estimated theoretically (Ghosh, A.; Gonzalez, E.; Vangberg, T. J. Phys. Chem. B 1999, 103, 1363) using density functional theory.

Rotational spectra of the deuterated carbon chain molecules: C 3D, C 4D, C 3HD, and C 4HD

Rotational Spectra of cis and trans Crotononitriles: Centrifugal Distortion, Hyperfine Structure, Internal Rotation and Structure

The rotational spectrum of diazirine-d2, [Formula: see text], has been recorded in the ranges 8–40 and 100–400 GHz. The hyperfine structure of the measured rotational lines has been analyzed. The analysis required the treatment of two pairs of equivalent nuclei, which is discussed in detail. The deduced deuterium nuclear-quadrupole coupling constants are[Formula: see text]The quadrupole coupling constants of the nitrogen nuclei[Formula: see text]are taken from the parent species, and the spin-rotation coupling constants are[Formula: see text]The rotational and centrifugal distortion constants have been obtained for the ground vibrational state from the analysis of the unperturbed line positions. The complete rs structure of diazirine has been determined using the rotational constants of all available isotopomers of diazirine. The internuclear distances are rs(C—N) = 148.13(24) pm, rs(C—H) = 108.03(29) pm, and rs(N—N) = 122.80(25) pm, and the bond angles are [Formula: see text] and [Formula: see text], with the HCH plane perpendicular to the NCN plane.

D-nuclear quadrupole coupling in the rotational spectrum of 15N 2…DF and an interpretation of the hyperfine coupling constants χ aaD and DaaHF within a series of complexes B…HF