Absorption coefficients of sulfur dioxide microwave rotational lines

New calculations of the absorption coefficients of the rotational transitions of ³²S¹⁶O₂ are given for all energy levels up to J = 50 and frequencies less than 200 GHz. A spectrometer incorporating a semiconfocal Fabry-Perot resonant cavity and operating in the vicinity of 70 GHz is described. The calculated absorption coefficients are compared to measured values obtained with this spectrometer and to existing measurements over the frequency range 26–40 GHz. The results obtained are in general agreement to within 5–10%. A detailed knowledge of the absorption coefficient behavior as a function of frequency is of particular interest in the development of high-sensitivity SO₂ monitors, and in investigations of the kinetics of fast chemical reactions.     

q-deformed boson-realization model applied to vibrational spectrum of sulfur dioxide

Aq-deformed boson-realization model is presented to study both stretching and bending vibrations of sulfur dioxide, where Fermi resonances are taken into account. Our results are compared with those of other models.     

Internal rotation effects in the pulsed jet rotational spectrum of the trifluoromethane-carbon dioxide dimer

The rotational spectrum of the normal isotopic species of the HCF₃-CO₂ weakly bound complex has been measured by Fourier-transform microwave (FTMW) spectroscopy. All transitions are split into A and E states by internal rotation of the trifluoromethane subunit. A global fit of these states gives rotational constants that are consistent with a structure predicted by an MP2/6-311++G(2d,2p) ab initio calculation in which the axes of the monomers are coplanar, with the hydrogen atom of the trifluoromethane angled toward one of the oxygen atoms of the CO₂. Measured dipole moment components (μ_a = 0.431(6) D, μ_b = 0, μ_c = 1.436(6) D, μ_total = 1.499(6) D) confirm the ab initio prediction of an ac plane of symmetry; however, the very near-prolate nature of the complex (κ = −0.997), combined with the relatively high barrier to internal rotation (∼30 cm⁻¹) leads to asymmetry splittings and internal rotation splittings of similar magnitude, resulting in the observation of dipole forbidden b-type E-state transitions in addition to the expected a- and c-type lines. Although this effect has been observed previously in several monomer spectra, this appears to be one of few examples for a weakly bound complex.     

The rotational spectrum of silacyclohexane

The rotational spectra of the normal and Si-d₂ isotopomers of the chair form of silacyclohexane have been measured by microwave absorption spectroscopy. A partial r₀ structure has been obtained. The rotational spectra of some, the most intense, vibrational satellites have also been measured. They belong to the ring-puckering motions. Their vibrational energies and their shifts of planar moments of inertia with respect to the ground state indicate that the amplitude of these vibrations is larger than in cyclohexane. The dipole moment has also been determined: μ_a = 0.75(2), μ_c = 0.280(2), and μ_tot = 0.80(2) D.     

The rotational spectrum of trichlorofluoromethane

The microwave and millimetre-wave spectra of CF³⁵Cl₃ have been measured in the ground and first excited doubly degenerate (E) vibrational states. Rotational, centrifugal distortion, and quadrupole parameters were obtained for both states. In the E state, strong l-resonance was observed, enabling some rotation-vibration parameters to be accurately determined. In addition, there was a splitting of the (kl − 1) = ± 1 lines due to the asymmetry of the individual quadrupole coupling tensors with respect to the principal inertial axes.     

The millimeter-wave rotational spectrum of fluorobenzene

The room-temperature rotational spectrum of fluorobenzene was studied in the frequency region 167-318 GHz. Rotational transitions were assigned and measured in the ground vibrational state, and all six excited vibrational states with energies below 600 cm⁻¹, i.e., v₁₁ = 1, v₁₁ = 2, v_18b = 1, v_16a = 1, v_16b = 1, and v_6a = 1. Accurate quartic-level spectroscopic constants were determined for all states, allowing spectral predictions well into the submillimeter region. The states v_18b = 1 and v_16a = 1 were found to be connected by a strong Coriolis interaction, which allowed precise determination of their energy separation, ΔE = 7.455088(3) cm⁻¹. Unambiguous assignment of vibrational modes was made on the basis of the calculated inertial defect and nuclear spin statistical weights. Rotational constants for the ¹³C₄ isotopomer have also been redetermined and two new least-squares determinations of the geometry of fluorobenzene, r₀ and are reported.     

High-resolution rotational spectrum of methyl cyanide

The ground-state microwave spectrum of methyl cyanide is remeasured between 70 and 240 GHz with a molecular beam spectrometer and by use of the Lamb dip method. It allows us to determine with great accuracy the B rotational constant, the quartic and sextic centrifugal distortion constants, the nuclear quadrupole coupling constant, and the spin-rotation constants of nitrogen. The magnetic shielding constants of nitrogen are also determined.     

The rotational spectrum of 2-indanone

The rotational spectrum of 2-indanone has been analysed in the 26.5-40 GHz frequency region. The ground state, the first five excited states of the five-membered ring bending mode and the first excited state of the ring twisting and butterfly modes have been assigned and analysed. From the ground state inertial defect and the variation of the rotational parameters with the ring bending quantum number a strictly planar C2v equilibrium conformation has been established. A one-dimensional potential function of the quadratic-quartic type V(X) = 3.3(7) (X4 + 11.66(15)X2)cm-1 has been derived for the bending vibration.     

The rotational spectrum of methyl trifluoroacetate

ABSTRACT

The pulsed supersonic jet expansion microwave spectra of the parent and all three ¹³C mono-substituted isotopologues of methyl trifluoroacetate have been measured in the 6.5–18 GHz range. All observed transitions are split into two component lines, due to the internal rotation of the methyl group. The corresponding barrier has been determined to be V ₃ = 4.379(3) kJ/mol. Structural information has been obtained from the 12 available rotational constants.     

The millimetre-wave rotational spectrum of phenylacetylene

The room-temperature rotational spectrum of phenylacetylene (C₆H₅CCH), was studied at frequencies up to 340 GHz. Extensive new measurements, covering rotational transitions with quantum number values up to J=140 and K_a=59, allowed determination of precise spectroscopic constants for the ground state and for the lowest two excited vibrational states, v₂₄=1 and v₃₆=1. The two excited states belong to the lowest B₁ and B₂ symmetry normal modes and their rotational transitions are very strongly perturbed by a-axis Coriolis resonance. A successful fit of the resonance is reported, resulting in and , in good agreement with results of ab initio computations.     

The rotational resonance Raman spectrum of nitrogen dioxide and the determination of electronic state symmetry from resonance Raman selection rules

The pure rotational Raman spectrum of nitrogen dioxide has been observed and shown to be consistent with existing determinations of molecular parameters. Upon observation at 600 Torr pressure and 0.4 cm⁻¹ resolution a well-defined rotational spectrum is obtained. This spectrum is overlaid with a number of fluorescence lines. The fluorescence lines are separated from the Raman spectrum by a comparison of Stokes and anti-Stokes branches of the rotational spectrum. Out of seven strong fluorescence lines seen with 5145 Å excitation, five probably are identifiable with vibration-rotation fluorescence progressions observed by Abe.The most striking feature of these observations is the potential use of the resonance Raman effect for the analysis of complicated electronic spectra. When this rotational spectrum is observed with excitation by 5309 Å or 5145 Å excitation, the Raman spectrum follows a-axis selection rules and the Q-branches are in the noise level or barely out of it. However, at 4880 Å the ΔK = 2Q-branches become a major feature of a spectrum, indicating that an appreciable part of the absorption at this wavelength is occurring through the operation of b- or c-axis selection rules. These findings are consistent with present notions of a ²B₂ excited state dominating absorption at longer wavelengths, while at shorter wavelengths a ²B₁ excited state becomes important. Given a tunable laser, one could map the relative importance of these two possible selection rules for NO₂ without any theoretical analysis more sophisticated than that presented in this paper.A simplified statement of the selection rules for resonance rotational Raman spectra of asymmetric tops has been developed in the course of this investigation. No attempt has been made to refine the rotational parameters of NO₂ since all of the lines seen areunresolved multiplets. Our data should be regarded as a search spectrum preliminary to investigation on a high resolution instrument.     

The rotational spectrum of the ground state of methylamine

Recent progress is reported in measuring, assigning, and fitting the rotational spectrum of the ground vibrational state of methylamine, CH₃NH₂, a spectrum complicated both by internal rotation of the methyl top and by inversion of the amino group. New measurements of 513 rotational transitions with J up to 30 and K up to 9 were carried out between 49 and 326 GHz using the millimeter-wave spectrometer in Kharkov. After removing the observed quadrupole hyperfine splittings, these new data along with previously published measurements were fitted to a group-theoretical high-barrier tunneling Hamiltonian from the literature, using 53 parameters to give an overall weighted standard deviation of 0.80 for 850 far-infrared and 673 microwave transitions in the ground state. The root-mean-square deviation of 0.018 MHz obtained for 346 millimeter-wave transitions measured with 0.020 MHz uncertainty represents an approximately 30-fold improvement in fitting accuracy over past attempts.     

Quadrupole hyperfine structure of the rotational spectrum of aminoacetonitrile

From high-resolution studies of the microwave spectrum of aminoacetonitrile we have established the quadrupole coupling constants of both nitrogen atoms in the molecule. They are χ_aa = ?2.77 (0.04) MHz, χ_bb = 1.20 (0.09) MHz for the amino nitrogen, χ_aa = ?3.48 (0.03) MHz, χ_bb = 1.50 (0.06) MHz for the nitrile nitrogen. Improved values for rotational constants and centrifugal distortion constants also emerge from the present spectral analysis.     

Microwave spectrum and hyperfine structure in the rotational spectrum of diatomic gallium iodide

The J = 3←2 rotational transition of diatomic GaI molecule has been measured in the microwave region. The molecules were produced by a reaction of gallium and lead iodide in the heated zone of a splitted wave guide. The lines were observed in the 10-GHz frequency region at a reaction temperature 270–350°C. Molecular parameters have been derived for ⁶⁹Ga¹²⁷I and ⁷¹Ga¹²⁷I from the analysis of the hyperfine structure. Systematic variations in quadrupole coupling constants in III_a halides have been observed. Vibrational dependence of the nuclear quadrupole interaction for ⁶⁹Ga¹²⁷I can be written as follows: $\text{eq}{}_{\mathrm{<mtext>v</mtext>}}\text{Q(}{}^{69}\text{Ga}\text{) = ?81.29(25) + 0.43(30)(v +}\text{1}\text{2}\text{)}\text{MHz}$, $\text{eq}{}_{\mathrm{<mtext>v</mtext>}}\text{Q(}{}^{127}\text{I}\text{) = ?369.35(10) ? 2.54(16)(v +}\text{1}\text{2}\text{)}\text{MHz}$.     

Linewidth parameters in the rotational spectrum of methyl cyanide

The linewidth parameters of some rotational components of the spectrum of methyl cyanide, J → J + 1 transitions (J = 0, 1, 2), were measured over a temperature range 195 ≤ T ≤ 300K and these experimental values were compared to available theoretical values. A multiple differentiation technique was employed in which derivatives of the rotational resonances were obtained in order to enhance resolution and to ascertain distortions within the line shapes. In some instances, high levels of modulation were required in order to obtain suitable resolution for the resonances and the method given by Netterfield was employed to correct for modulation broadening. The presence of hyperfine structure in the (J = 2 → J = 3) transition was found to produce overlapping of resonances which persisted to pressures less than 1 mTorr. Pressure ranges from 1 to 50 mTorr were explored in this investigation.     

Pure rotational spectrum of carbonyl sulfide in the far-infrared

The pure rotational spectrum of OCS has been studied by Fourier transform at room temperature over the frequency range 20–42cm⁻¹. The ground state rotational lines were observed for OC³²S up to J = 103. It has been possible also to identify the rotational lines for OC³⁴S in the ground state and for OC³²S in the ν₁ = 1 level.     

Far infrared pure rotational spectrum of methylacetylene

The pure rotational spectrum of methylacetylene has been recorded in the far infrared region between 10 and 60 cm^?1 with a Fourier transform spectrometer whose theoretical resolution was 0.025 cm^?1. From the measured wavenumbers it has been possible to determine the rotational constants in the ground state and in the v₅ = 1, v₈ = 1, v₁₀ = 1, 2, 3, 4 levels.