Microwave spectrum of nitroxyl

The FS2 radical has been detected in the glow discharge of the SF6 gas by microwave spectroscopy. Both a-type and b-type rotational transitions with the fine and hyperfine structure were observed in the millimeter-wave range of 120–185 GHz. The least-squares analysis for the 440 line frequencies led to the determination of the rotational constants, the centrifugal distortion constants, the spin-rotation interaction constants with the centrifugal distortion corrections, and the hyperfine interaction constants. Especially, the off-diagonal constants (εab+εba)/2 and Tab were determined in good precision because some nearly degenerate energy levels were mixed strongly by the off-diagonal spin-rotation interaction, which separated the energy levels up to 3 GHz and even induced the forbidden transitions to be observed strongly. The spin density on the fluorine atom and the chemical bond moments were derived for FS2, and the possible signs of Tab and (εab+εba)/2 were discussed. The behaviors of the FS2 radical and other related transient species in the SF6-discharge system were compared by using the corresponding rotational transitions observed in the microwave spectra.

The microwave spectra of vinyl iodide, CH2=CHI, in its ground and first excited vibrational states, have been measured in the frequency range 20–108 GHz. The spectrometer used was a 100 kHz Stark modulated instrument, interfaced to a Digital Micro-PDP 11/23+ computer for control and for data acquisition and storage; this interfacing is described. The spectrum contains strong a-type transitions and very weak b-type transitions; all contain 127I quadrupole hyperfine structure, with several large perturbations. A procedure specially devised for analysis of such spectra, which takes advantage of the perturbations, was applied to produce accurate values of constants that might otherwise be unobtainable, and to permit assignment of the b-type transitions. Both components of the dipole moment have been measured. The centrifugal distortion constants and inertial defects have been compared with those calculated from a published harmonic force field, modified for the out-of-plane vibrations. A partial structure has been obtained.

Microwave spectrum of GeF 2: quadrupole coupling and centrifugal distortion

By analysing the millimetre wave spectrum of vinyl fluoride in the range from 100 to 160 GHz its rotational constantA has been determined and found to be 64 582.7 MHz. The centrifugal distortion constants are also given. Measurements of Stark effect on four lowJ «a » type transitions give for the total dipole moment the valueμ=(1.427±0.010)D.

Rotational spectra of p-, m-, and o-cyanophenol have been measured in the range of 10.5-21 GHz and fit using Watson's A-reduction Hamiltonian coupled with nuclear quadrupole coupling interaction terms for the (14)N nuclei. Ab initio calculations at the MP2/6-311++G(d,p) and CCSD(T)/6-311++G(d,p) levels predict the cis conformers of m- and o-cyanophenol to be more stable than the corresponding trans conformers. A natural bond orbital analysis of the hydrogen bonding interaction in o- and m-cyanophenol revealed an intramolecular hydrogen bond that preferentially stabilizes the cis conformer of o-cyanophenol but there was no evidence of hydrogen bonding interactions in cis m-cyanophenol. We recorded 25 a- and b-type rotational transitions for cis o-cyanophenol; the rotational constants are A = 3053.758(2) MHz, B = 1511.2760(3) MHz, and C = 1010.7989(2) MHz. The trans conformer of o-cyanophenol was not observed. We recorded 14 a- and b-type rotational transitions for cis m-cyanophenol and 16 a- and b-type rotational transitions for trans m-cyanophenol. The rotational constants are A = 3408.9200(2) MHz, B = 1205.8269(2) MHz, and C = 890.6672(1) MHz and A = 3403.1196(3) MHz, B = 1208.4903(2) MHz, and C = 891.7241(2) MHz for the cis and trans species, respectively. Rotational transitions of the p-cyanophenol monomer are split due to the internal rotation of the hydroxyl group with respect to the aromatic ring. We recorded 25 a- and b-type rotational transitions for p-cyanophenol; the b-type transitions are split by 40 MHz. The rotational constants are A = 5612.96(2) MHz, B = 990.4283(6) MHz, and C = 841.9363(6) MHz. The ground state spitting DeltaE is 20.1608(6) MHz and the barrier to internal rotation, V(2), is 1413(2) cm(-1) from a fit of the rotational transitions to an internal axis system Hamiltonian. The barrier to internal rotation was modeled at the MP2/6-311++G(d,p) level and the effects of substituents on the phenolic ring and the barriers to internal rotation are discussed.

The rotational spectrum of jet-cooled hafnium dioxide obtained by laser ablation of a solid ceramic rod has been investigated by Fourier-transform microwave spectroscopy in the 8 to 28 GHz frequency range. Rotational transitions within the ground and several excited vibrational states of the lowest vibrational mode of the molecule have been assigned. The resulting spectra have been fit, yielding rotational parameters for the five most abundant isotopomers of HfO2. Centrifugal distortion effects are noticeable even for the lowest-J transitions. Very large quadrupole coupling effects for the isotopomers with nuclear quadrupole moments (179Hf (I=9/2) and Hf177 (I=7/2)) have been accounted for using the diagonal elements of the nuclear quadrupole coupling tensor. A ground-state effective C2v geometry has been obtained for HfO2, yielding ro(Hf–O)=1.7764(4) Å and ∠(O–Hf–O)=107.51(1)°. The electric dipole moment has been determined for HfO2180 from Stark-effect measurements, giving μ=26.42(3)×10-30C⋅m [7.92(1) D]. Ab initio calculations using density functional theory and relativistic core potentials are in satisfactory agreement with the experimental results. Finally, in the course of this investigation, the rotational spectrum of the diatomic molecule, HfO, has also been reexamined, and new results for vibrational satellites (up to v=18 in some cases) of the J=1←0 rotational transition are reported. A vibrational analysis using Le Roy’s form of the Dunham expansion has allowed the determination of atomic mass-dependent Born–Oppenheimer breakdown parameters for both atoms of HfO.

The microwave spectra of four isotopic species of 1,1-dimethyldiborane have been investigated in the region between 18.0 and 40.0 GHz. The observed rotational constants (MHz) for the normal species are A=7070.68(7), B=6606.57(3), C=3660.33(1); for 10B1 species, A=7069.87(15), B=6605.79(5), C=3659.88(3); and for 10B2 species, A=7070.63(27), B=6889.89(10), C=3745.92(6). The B–B distance determined by the Kraitchman method is 1.76(2) Å. The carbon–boron structure could be fitted to the moments of inertia by assuming reasonable values for the other structural parameters: r(B1−C)=1.59 Å and <CBC=121.2°. From the Stark effect measurements, the dipole moment is measured to be 0.87(3) D. Assuming no coupling between the rotors, the barrier height to internal rotation is 1.39(16) kcal/mol.

A study is presented of the lowest-energy singlet—singlet transition of pyridine N-oxide in mixed crystals with p-dichlorobenzene at 4.2°K. Polarization and Stark effect measurements on the electronic orgin of the transition (at 29 599.6 cm−1) show that the transition is π*← π, 1B2← 1A1. The spectrum of d5-pyridine N-oxide is blue shifted by 123 cm−1 and its absorption and emission spectra are quite similar to those of h5. The vibrational analysis of the absorption and fluorescence spectrum, and the Franck—Condon patterns, suggest that the equilibrium geometry is little affected by electronic excitation. Stark effect measurements on the electronic origin band yield a value of Δ μ=0.71 ± 0.03 D (assuming E ≡ 0.60 Eeff) for the change in dipole moment on electronic excitation; where E and Eeff are the applied and effective Stark electric fields corresponding to an external field directed down the a′ crystallographic axis of the p-dichlorobenzene host crystal. This small change is much less than predicted by π-electron theory.

The rotational spectrum of 4-methyl-1,3-dioxane, C₅H₁₀0₂, has been recorded from 16.0 to 40.0 GHz. The a-, b- and C- type transitions with J≤57 have been observed and assigned for the normal species in the ground vibrational state. The rotational constants and the quartic centrifugal distortion constants were determined to be A = 4802.335(2) MHz, B = 2376.163(1) MHz, C = 1738.852(1) MHz and Δ_J = 0.1496(6) kHz, Δ_JK = 0.157(5) kHz, Δ_K = 0.76(3) kHz, δJ = 0.0423(1) kHz, δK 0.260(3) kHz. Stark effect measurements were used to determine the projections of the dipole moment on the principal inertial axes (in Debye units): μ_a = 0.73(1), μ_b = 1.32(1), _c = 1.36(1) and μ_tot = 2.03(2). Comparison of the experimental rotational constants and dipole moment components with results of ab initio calculations (B3PW91/aug-cc-pVDZ) shown that 4-methyl-l,3-dioxane exist in chair form with equatorial orientation of methyl group.

The microwave spectra of CD3CH2CN, 13CH3CH2CN, CH3 13CH2CN and CH3CH2C15N have been measured. In addition the spectrum of CH3CH2 13CN has been remeasured with greater accuracy. From these spectra and those previously reported - CH3CH2CN, CH3CD2CN, CH2DCH2CN (sym) and CH2DCH2CN (asym) - a complete rs-structure has been calculated by the equations of Kraitchman and Chutjian. r0-structure calculations were performed with different assumptions due to the symmetry of the molecule. A comparison between r0- and rs-structure was made and showed good agreement especially for the atoms of the frame. The quadrupole coupling constants of the above mentioned isotopes of ethyl cyanide were obtained from the hyperfine structure of the spectra with the exception of CH3CH2C15N, which has no nucleus with quadrupole moment. The quadrupole coupling tensor in its principal axis system was determined from the constants of CD3CH2CN and CH3CD2CN using the angle e between their principal axes of inertia in the a-b-plane. From Stark effect measurements the dipole moment of CH3CH2CN was reevaluated. To determine the direction of the dipole moment Stark effect measurements for CD3CH2CN and CH3CD2CN were carried out.

Excited state dipole moments of fluoroanilines from solvatochromic shift measurements

The rotational constants of Δ6-bicyclo[3.2.0]heptene have been derived for the ground state (in MHz: A=4419.20, B=3080.16, C=2375.33) and several excited states of the low-frequency vibrations of this molecule. The rotational constants were also derived for one monosubstituted 13C species in natural abundance. Stark effect measurements have yielded dipole moment components for the ground state of μa=0.201±0.001 D, μc=0.052±0.004 D, giving a total dipole moment of μ=0.208±0.001 D. These data are used to draw conclusions as to the conformation of this bicyclic compound.

Towards the complete analysis of the rotational spectrum of (CH 3) 3SnCl

Two new carbon chain radicals terminated with a nitrile group, C4N and C6N, have been detected in a supersonic molecular beam by Fourier transform microwave spectroscopy. In addition, at least three hyperfine-split rotational transitions of the singly-substituted isotopic species of C3N have also been observed. Both C4N and C6N are linear chains with Π2 electronic ground states, and both radicals have resolvable hyperfine structure and lambda-type doubling in their lowest rotational levels. At least four transitions in the lowest-energy fine structure component (2Π1/2) were measured between 7 and 22 GHz for both molecules, and at most nine spectroscopic constants were required to reproduce the measured spectra to a few parts in 107. Precise sets of rotational, centrifugal distortion, spin-rotation, and hyperfine coupling constants were also determined for the isotopic species of C3N by combining the centimeter-wave measurements here with previous millimeter-wave data. The C13 hyperfine coupling constants of isotopic C3N differ from those of the isoelectronic chain C4H, but are fairly close to those of isovalent C2H, indicating a nearly pure Σ2 electronic ground state for C3N. Although the strongest lines of C6N are more than five times less intense than those of C5N, owing to large differences in the ground state dipole moments, both new chains are more abundant than C5N. Searches for C7N have so far been unsuccessful. The absence of lines at the predicted frequencies implies that the product of the dipole moment times the abundance (μ⋅Na) is more than 60 times smaller for C7N than for C5N, suggesting that the ground state of C7N may be Π2, for which the dipole moment is calculated to be small.

The experimental electric dipole moments of the Ar nHX van der Waals clusters