The ground-state rotational constants of silane

From thirty-nine combination difference equations we have determined three significant ground-vibronic state constants of silane: β ⁰/hc=2·85941 cm^-1, γ ⁰/hc=-3·82×10^-5 cm^-1 and ε ⁰/hc=-7·97×10^-7 cm^-1 or in Hecht's notation B ₀=2·85941 cm^-1, D _s=3·82×10^-5 cm^-1 and D _t=2·436×10^-6 cm^-1.     

The ground-state rotational constants of germane

The ground-state rotational constants B₀, D₀, and H₀ have been determined for GeH₄ from the analysis of ground-state combination differences in the infrared spectra of isotopically enriched ⁷⁰GeH₄, ⁷²GeH₄, and ⁷⁴GeH₄. The spectra were recorded at 0.06-cm^?1 resolution and about 0.005-cm^?1 precision for unblended lines. Suitable combination differences were found in both the ν₂ and the ν₄ infrared bands. The ground-state constants were assumed to be invariant to isotopic substitution at Ge, and the tensor distortion constants were held fixed at their microwave values. The results obtained are: B₀ = 2.69587 ± 0.00007 cm^?1, D₀ = (3.34 ± 0.03) × 10^?5 cm^?1, H₀ = (1.3 ± 0.5) × 10^?9 cm^?1.     

The ground state rotational constants of NNO

We report new measurements of the 5 ← 4 through 9 ← 8 lines in the pure rotational spectrum of nitrous oxide, ¹⁵N¹⁵N¹⁶O, and measurements at room temperature and at an elevated temperature of the 10⁰0-00⁰0 and 02⁰-00⁰0 bands of that molecule. The new data together with data for 10 other vibration-rotational transitions which previously have been reported enable us to determine the ground state constants. Using the newly determined values of B₀₀₀, D₀₀₀, and H₀₀₀, we have determined the band origins and the upper state constant differences B - B₀₀₀, D - D₀₀₀, and H - H₀₀₀ of 25 vibration-rotational bands whose lower level is the ground vibrational state.     

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 rotational energy levels of four methyl groups

The energy level spectrum for a system of four interacting methyl groups belonging to an X(CH₃)₄ type molecule is calculated by numerical methods. The rotational potential at the site of each methyl group is assumed to be of a three-fold symmetry. The torsion-torsion interaction is defined as a term in the multipole expansion of the electrostatic interaction of two rigid charge distributions. It is shown, that the tunneling frequency characterizing the ground state manifold in the absence of methyl-methyl interaction, splits into a set of closely spaced frequencies.     

The estimation of equilibrium molecular structures from zero-point rotational constants

The approximate equation I_e = 2I₈ - I₀, where I_e, I₈, and I₀ are, respectively, the equilibrium, substitution and zero-point moments of inertia of a molecule, can be derived from a first order treatment of isotope effects, and is valid for linear, symmetric or asymmetric tops. By means of this equation it is possible to estimate the equilibrium structure of a molecule from the zero-point rotational constants of several isotopes. The advantage of this “mass-dependence” (r_m) method over the conventional r_e method is that it is insensitive to the perturbations and resonances that frequently affect excited vibrational states. The main disadvantages are that a large number of isotopic molecules may be necessary and that the above equation is not sufficiently accurate for hydrogen-deuterium isotope effects.A detailed comparison between r_m and r_e of CO shows that the slight difference of about 2 × 10^?4Å between the two bond lengths is due mainly to the difference in the contributions of the electrons. The r_m method has also been applied to the triatomic molecules N₂O, OCS, SO₂ and HCN. For N₂O and SO₂ the results are in excellent agreement with the most recent r_e structures. For OCS there is a significant difference between the r_m structure and the present r_e structure. This difference is as yet unexplained. The poor results for HCN confirm the general expectation that the r_m method cannot be applied to hydrides without further modification.     

Anharmonic constants of methyl chloride

Eighteen anharmonic constants of methyl chloride have been deduced from the measurements of band centers found in the literature.     

The temperature dependence of the methyl rotational potential in methyl iodide under pressure

Inelastic neutron scattering experiments have been performed on CH₃I under pressure. The tunnel splitting of the methyl librational groundstate decreases almost exponentially with increasing hydrostatic pressure: _t (p)=2.48 eV·exp (–0.138·p[kbar]), the librational energy increases asE ₀₁ (p)=13.2 meV (1+0.050p[kbar]). Both relations can be explained by a rotational potentialV which depends on the interatomic distancer asVr ^–9.6 . This large exponent shows the importance of valence forces. The shape of the rotational potential is almost unaffected by pressure. The coupling of the methyl group to phonons via a shaking and a breathing term which was observed at atmospheric pressure is also found at high pressure. The effect appears at higher temperature as expected for the stronger potential.     

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.     

Ground-state rotational constants of 12CH3D

An analysis of ground-state combination differences in the ν₂(A₁) fundamental band of ¹²CH₃D (ν₀ = 2200.03896 cm^?1) has been made to yield values for the rotational constants B₀, D₀^J, D₀^JK, H₀^JJJ, H₀^JJK, H₀^JKK, L^JJJJ, L₀^JJJK, and order of magnitude values for L₀^JJKK and L₀^JKKK. These constants should be useful in assisting radio searches for this molecule in astrophysical sources. In addition, splittings of A₁A₂ levels (J ≥ 17, K = 3) have been measured in both the ground and excited vibrational states of this band.     

Ground-state rotational constants of CH3D

An analysis of the ground-state combination differences in the ν₂(A₁) band of ¹³CH₃D (ν₀ = 2190.0485 cm⁻¹) has been made to yield accurate values for six ground-state rotational constants, B₀, D₀^J, D₀^JK, H₀^JJJ, H₀^JJK, and H₀^JKK.     

Calculation of the cubic symmetry force constants of methyl bromide and methyl chloride

The cubic symmetry force constants have been calculated for methyl bromide and methyl chloride through the method developed by Hoy et al. (Mol. Phys. 24, 1265–1290 (1972)). The spectroscopic constants recently reported in the literature have been utilized for the present analysis. Out of a total of 38 independent cubic force constants, 6 and 10 constants were constrained to zero for a methyl bromide and methyl chloride, respectively, in which a diagonal force constant of F₆₆₆ was included for both molecules. However, it is noted that those force constants which are only concerned with the A₁ symmetry coordinates have been determined independent of the constraint for both of these molecules.     

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.     

The Tl1 + I dissociative state in thallium lodide

Experiments have been performed to determine the fluorescence yield of the 535-nm transition in photodissociated thallium iodide vapor as a function of the excitation wavelength in the range from 182 to 209 nm. The spectral dependence of the fluorescence yield, together with the known structure of the molecular ground state, allowed the calculation of the slope of the Tl¹ + I dissociative potential.     

Far-infrared spectrum and ground state constants of methyl amine

The far-infrared spectrum of methyl amine has been studied in the region 40 to 350 cm⁻¹ by Fourier transform spectroscopy with an apodized resolution of 0.005 cm⁻¹ or better. Both the pure rotational spectrum and the spectrum of the fundamental torsional band have been assigned. This paper reports the ground state constants obtained from a global fitting of a data set including ground state microwave transitions from the literature, as well as far-infrared pure rotational ground state transitions and ground state combination differences from the torsional band obtained in this work. Slightly over 1000 energy differences for the ground state with 0 ≦ K ≦ 19 and K ≦ J ≦ 30 were fit to 30 molecular parameters from a group theoretical formalism developed earlier, and a standard deviation of ±0.00063 cm⁻¹ was obtained. An ambiguity (noted earlier in the microwave literature) in the determination of the structural parameter ϱ, which arises when two large amplitude motions are present in the molecule, can be understood and resolved using the present formalism.     

The spectra and structure of indium iodide: The rotational and vibrational constants of the B 1 state

The rotational constants of the B 1 state of indium iodide are reported for the first time as B_e = 0.037533 cm⁻¹ and α_e = 0.000289 cm⁻¹ while T_e = 25050.60 cm⁻¹ for the B1-X0⁺ transition. Accurate vibrational constants are also computed from measured Q heads as ω_e= 146.36 cm⁻¹ and ω_eχ_e = 2.20 cm⁻¹.