Rotational spectrum of acetonitrile CH3CN and CH3CN in a doubly excited degenerate vibrational state

The rotational spectrum of the acetonitrile molecules CH₃C¹⁴N and CH₃C¹⁵N in the degenerate vibrational state v₈ = 2 has been studied for the transitions J = 0 → 1, 2 → 3, 3 → 4, 4 → 5, 5 → 6, 6 → 7, and 7 → 8.     

First- and second-order Coriolis interactions in symmetric top molecules: Application to the microwave spectrum of cyclopentadienyl thallium

Matrix elements are derived for both first- and second-order Coriolis interactions between A₁ and E₁ vibrational modes in symmetric tops, with particular reference to sign. The results are applied to the observed microwave transitions J → J + 1 for A₁ and E₁ states of the C_5ν molecule cyclopentadienyl thallium in various excited vibrational states. The microwave transitions in the excited A₁ states v₄ = 1, 2, 3, the excited E′ state v′₀ = 1 and the combination state v₄ = 1, v′₀ = 1 have yielded constants which are anomalous in several respects (1). Coriolis interactions between the ν₄ and ν₁₀ vibrations are shown to account for the observed anomalies.     

Microwave spectrum of silyl fluoride: Coriolis resonance between ν2 and ν5 states

The J = 1 ← 0 and J = 2 ← 1 microwave rotational transitions of SiH₃F and SiD₃F have been measured for the ground and the v₂ = 1, v₃ = 1, v₅ = 1, and v₆ = 1 vibrational states, for which the various rotational and vibration-rotation interaction constants have been obtained. Both molecules show an X-Y Coriolis resonance between the ν₂ and ν₅ vibrational states, whose separation are 29 and 8 cm^?1, respectively. In the case of SiD₃F the resonance is very strong and an exact numerical diagonalization of the energy matrix was employed.     

Role of intramolecular interactions in Raman spectra of N2 and O2 molecules

The effect of vibration-rotation interactions and anharmonicities on the polarizabilities matrix elements, Raman scattering cross-sections, and depolarization degrees of N₂ and O₂ molecules for vibrational transitions v→v, v+1, v+2, v+3 have been investigated.     

The two-dimensional anharmonic oscillator: The microwave spectrum of silyl isocyanate,SiH3NCO

The J + 1 ← J transitions (J = 2, 3, 4, 5, and 6) in the microwave spectrum of SiH₃NCO have been assigned for the vibrational ground state and for the vibrational states v₁₀ = 1, 2, and 3. The results for v₁₀ = 0 confirm earlier work. The vibration-rotation constants show a remarkable variation with v₁₀ and l₁₀. To a large extent the anomalous behavior of these constants has been explained in terms of a strongly anharmonic potential function for the ν₁₀ vibrational mode.     

Infrared-microwave double resonance in CH3OH using a Zeeman-tuned 3.5-μm HeXe laser

Infrared microwave double resonance signals have been observed for CH₃OH using the 3.5-μm HeXe laser line. When microwave transitions in the ground vibrational state are pumped, the double resonance signals are obtained on two infrared transitions v = 1 ← 0 of ν^CH(a′); v = 1, J, K, μ = 4, 2, 1 ← v = 0, J, K, μ = 3, 2, 1, and 4, 3, 1 ← 3, 3, 1. Three weak double resonance signals are due to the collision-induced transitions. Their relative intensities have been explained successfully by using the rate constants of collision-induced transitions which are proportional to the dipole matrix elements between the states involved in the transitions.     

Rotation-vibration analysis of the microwave spectrum of cyanobutadiyne,H(CC)2CN

The detailed rotational spectrum of the linear molecule cyanobutadiyne, H(CC)₂CN, has been observed in the range 26.5 to 40.0 GHz. In particular, a study has been made of transitions belonging to the vibrationally excited states (including combination states) of the degenerate vibrations ν₁₀ and ν₁₁. Particular attention has been focused upon two series of satellites: one in which v₁₁ = 1–8 and a second in which v₁₀ = 1 while v₁₁ varies from 1–7 for a given J transition. The analysis was performed using a least-squares criterion to fit all the transitions simultaneously. In addition to providing confirmation of the forms of the vibrational and rotational l-resonance matrix elements, the analysis has demonstrated that the widely spaced l quartets observed in combination states with odd Σ_iv_i can be attributed to a strong mixing of the four l = 1 states by vibrational l resonance. It has also been found that it is only possible to determine the sign of the product of the offdiagonal parameters and not the sign of any one parameter. Therefore the reported assignment is not unique. As confirmation of the validity of the analysis, the computer simulation of the spectrum is compared with that observed.     

The microwave spectrum of sodium tetrahydroborate NaBH4 in excited vibrational states: Coriolis interaction between the Na-BH4 stretching and the BH4 rocking vibrations

Two sets of vibrational satellites have been observed in the rotational spectrum of sodium tetrahydroborate NaBH₄, and have been assigned to the non-degenerate, Na—BH₄ stretching and the degenerate BH₄ rocking (or internal rotation) states. The observation was extended from the J = 11 ← 10 up to J = 20 ← 19 transitions. The vibrational satellites showed anomalous K structure; higher-K lines of the non-degenerate state appeared at higher frequencies, in reverse to those of the ground state, whereas the spectra in the degenerate state exhibited a K pattern similar to but somewhat more widely spread than that of the ground state. These anomalies are ascribed to the Coriolis interaction between the two excited vibrational states. The spectra observed were analysed using a C_3v symmetric-top rotational Hamiltonian, which took into account the Coriolis interaction explicitly. The A rotational constants, the energy difference δE between the two interacting vibrational states, and the first- and second-order Coriolis interaction constants have been derived.     

A comprehensive model to predict the microwave spectrum of propyne in the region 17–70 GHz for the ground and v10 = 1, 2, 3, 4, 5 vibrational states

A comprehensive model for predicting rotational frequency components in various v₁₀ vibrational levels of propyne was developed. A number of components of the rotational spectra in the ground and v₁₀ = 1, 2, 3, 4 excited vibrational states of propyne in the frequency range 17–70 GHz have been obtained. Molecular constants for these vibrationally excited states have been determined from more than 100 observed rotational transitions. From these experimentally observed components and a model based upon first principals for C_3v molecules, rotational constants have been expressed in a form which enables one to predict rotational components for vibrational levels for propyne up to v₁₀ = 5. The model also appears to be useful in predicting rotational components in more highly excited vibrational levels but data were not available for comparison with the theory. Experimentally measured frequencies are presented and compared with those calculated using the results of basic perturbation theory.     

The pentad rotation-vibrational states of 12CD4: Wavenumber analysis of infrared and Raman spectra of the ν1, ν3, 2ν2, ν2 + ν4, and 2ν4 bands

The so-called pentad of ¹²CD₄ consists of the vibrational states v₁ = 1(symmetry A₁), v₃ = 1(F₂), v₂ = 2(A₁ + E), v₂ = v₄ = 1(F₁ + F₂), and v₄ = 2(A₁ + E + F₂). All states are located in the 1950 to 2250-cm^?1 region and all are strongly interacting. In the present work we have assigned more than 5000 infrared rotation-vibrational transitions and 163 isotropic Raman transitions from the vibrational ground state to the pentad. We have used infrared and Raman spectra of a resolution better than 0.01 cm^?1. From the experimental wavenumbers 2567 pentad rotation-vibrational energy levels with J ≦ 20 have been determined. These levels are reported in the paper. The levels have been used for refinements of the spectroscopic constants of two physically different effective Hamiltonians for the pentad states. For all levels with J ≦ 12 an unweighted standard deviation of 0.004 cm^?1 is obtained for both Hamiltonians, whereas the standard deviation increases more or less rapidly with J above 12 due to the imperfections of the Hamiltonians. The values of the spectroscopic constants of both Hamiltonians (85 and 106, respectively) are reported and the effects of the approximations are discussed.     

l-type doubling of the kl = −1 levels in the microwave spectrum of the C4v molecule BrF5

Measurements are reported for the J 3 → 4, 4 → 5, and 5 → 6 transitions of BrF₅ in the excited vibrational states v₅(B₁) = 1 and v₉(E) = 1. These two states are nearly degenerate and an unusually strong Coriolis interaction perturbs both excited state spectra. New expressions are obtained for the E-species absorption frequencies which are valid in a strong Coriolis resonance situation. The analysis of the E-state spectrum has provided the first experimental observation of the doubling of the kl = −1 levels predicted for molecules with C_4v symmetry.     

The v10=1 Level of Propyne, H3CCCH, and Its Interactions with v9=1 and v10=2

Almost 300 new rotational transitions within the fundamental vibrational level v₁₀=1 of propyne have been measured in selected regions between 495 and 925 GHz spanning the quantum numbers 28≤J≤54 and 0≤K≤16. The accuracies are mostly between 10 and 20 kHz. In addition, the J″=4 and 5 transitions near 85 and 103 GHz have been remeasured. Simultaneous analyses with refined rovibrational data have been performed, showing that even this lowest and seemingly isolated vibrational level needs a global treatment when high K transitions are involved. The global model with the v₁₀=1 level coupled to the next higher cluster of levels, v₁₀=2/v₉=1, by Fermi and Coriolis resonances is necessary for a quantitative reproduction of both the rovibrational and rotational data within their experimental uncertainties. Included are also improved ground state spectroscopic parameters from a fit of previous pure rotational data and Δk=3 ground state combination loops as well as additional data obtained in course of the present study.     

Microwave spectrum of CH3OD

The microwave spectrum of CH₃OD has been observed in the frequency region between 14 and 92 GHz. All the ground-state transitions with J ≤ 8 and J = 2 ← 1, a-type transitions in the excited torsional states (v = 1 and v = 2) have been observed. The spectrum has been analyzed and rotational constants, torsional constants, torsion-vibration-rotation interaction constants, and centrifugal distortion constants have been evaluated. The Stark effect measurements have been made and the dipole moment components have been determined as μ_a = 0.833 ± 0.008 D and μ_b = 1.488 ± 0.015 D.     

Microwave spectrum of Trioxane in four excited degenerate vibrational states,especially in the 2ν20 (E) state and the combination state ν7 (A1) + ν20 (E)

The microwave spectra of the Trioxane molecule in the doubly excited degenerate vibrational state 2ν₂₀(E) and in the combination state ν₇(A₁) + ν₂₀(E) are reported for several J values. Molecular constants of these states have been determined. The excited states ν₂₀(E) = 1 and ν₁₉(E) = 1 previously studied by a perturbation formula have been analyzed by a direct diagonalization method of the energy matrix. Parameters which give the variation of the rotational constant B_V as a function of the quantum number v have been obtained.     

The far-infrared spectrum and spectroscopic parameters of PH3 in the ground state

The far-infrared spectrum of phosphine, PH₃, was recorded in the region between 30 and 200 cm⁻¹ at a resolution of 0.002 cm⁻¹. ΔJ = +1, ΔK = 0 rotational transitions in the ground state were measured and assigned up to J″ = 22 and K = 19. These transitions were analyzed together with the presently available microwave and submillimeter-wave data on the basis of different formulations of the rotational Hamiltonian, which included Δk = ±3 and/or Δk = ±6 interaction terms. An upper limit for the constant of the inversion splitting was obtained by fitting the same transitions to an appropriate inversion-rotational Hamiltonian. Rotational transitions in the v₂ = 1 and v₄ = 1 vibrational states were also observed.     

Microwave spectroscopy of propynal in the v2 = 1 vibrational state by IR-MW triple resonance

Infrared-microwave triple resonance was applied to microwave spectroscopy of propynal, HCCCHO, in the v₂ = 1 vibrational state. Eleven microwave transitions were newly observed by using a Zeeman-tuned 3.51 μm HeXe laser as the infrared radiation source. The spectrum was analyzed including the 11 transitions previously observed by double resonance. A least-squares fit of the 13 low-J transitions revealed that the rotational constants in the K_?1 = 1 states were slightly different from those of the K_?1 = 0 states. A higher-order rotational resonance was proposed for explanation of the effect.     

The microwave spectrum of methyl isocyanate

The microwave spectrum of methyl isocyanate, CH₃NCO, has been measured in the range from 8 to 40 GHz. More than 200 lines have been assigned to the a-type J + 1 ← J rotational transitions (J = 0 to 3) arising from molecules in the ground state and excited torsional and CNC bending states. The observed spectrum has been analyzed and successfully interpreted in terms of the five-dimensional quasi-symmetric top molecule model accounting explicitly for the large-amplitude CNC bending motion, and internal and overall rotation. In the least-squares fitting to the observed transition energies the values of the parameters of the CNC bending-torsional potential function have been determined.     

Ground state spectrum of methylcyanide

The rotational spectrum of methylcyanide (acetonitrile) in the ground vibrational state was measured in the spectral region from 91 to 810 GHz using the Cologne and Tsukuba spectrometers operated in the Doppler-limited and sub-Doppler saturation layouts. The resolution of the saturation Lamb-dip measurements is estimated to be about 1 kHz at the best of circumstances and the measuring accuracy of 10-60 kHz depending very sensitively on the quality of the spectrum. In the cases of rotational transitions with the low quantum number J (J<18) and with a low difference of the rotational quantum numbers J−K, the resolved or partly resolved hyperfine structures of the rotational transitions were observed. Together with the most accurate data from the literature, the newly measured experimental data were analyzed using the traditional polynomial energy formula as well as the Padè approximant for the effective rotational Hamiltonian. The resulting rotational, centrifugal distortion, and hyperfine structure spectroscopic constants were obtained with a significantly higher accuracy than the ones listed in the literature. In addition, an anomalous accidental resonance was detected between the K=14 ground state levels and the K=12, +l levels in the excited v₈=1 vibrational state.     

Effective Hamiltonian for degenerate vibrational states in symmetric top molecules

A mixed matrix-operator form of the effective rotational Hamiltonian has been discussed for the degenerate vibrational states of symmetric top molecules. In this scheme, a rotational contact transformation can be applied to the effective Hamiltonian such that the operators of the “2, +2,” “2, −2,” and “2, −1” l-type interactions as well as the operators of the Δk = ±3 and ±4 interactions are eliminated from the first-order terms of the expansion of the rotational Hamiltonian in terms of the small parameter λ. The results have been used to discuss the correlation between various interaction parameters in the effective rotational Hamiltonian for the doubly degenerate fundamental vibrational levels of semirigid symmetric top molecules. For example, for C_3v or D₃ molecules, the parameter of the “2, −1” interaction is correlated with other parameters and cannot be determined separately by fitting the experimental data (unless there are certain accidental resonances between vibrational-rotational levels).     

Global fit of the high-resolution infrared spectrum of D2S

High-resolution Fourier-transform spectra of the D₂S molecule in the regions of polyads of interacting vibrational states v = 3/2, 2, 5/2, 3 and 7/2 (v = v₁ + v₂/2 + v₃) were recorded for the first time with a Bruker IFS 120 Fourier-transform interferometer and analysed. A global fit of all currently available rotation-vibration energies has been made for 22 vibrational states of the D₂S molecule. The resulting set of 231 parameters reproduces all the initial experimental data (about 3670 vibration-rotation energies which correspond to more than 9700 ro-vibrational transitions with J^max = 25) with accuracies close to the experimental uncertainties.