Microwave spectrum of methyl chloride in the excited vibrational states: Coriolis interaction between the ν2 and ν5 states

The rotational spectra of CD₃³⁵Cl, CD₃³⁷Cl, CH₃³⁶Cl, and CH₃³⁷Cl in the ν₂, ν₃, ν₅, and ν₆ states were observed and analyzed. A few lines of the J = 3 → 2 transition were also detected for ¹²CD₃³⁵Cl in the 2ν₃ state and for ¹³CD₃³⁵Cl in the ν₃ state. For CH₃³⁵Cl in the ν₆ state the present data on the J = 1 ← 0 and J = 2 ← 1 transitions were combined with the millimeterwave spectra reported by Sullivan and Frenkel to determine the molecular constants. Special attention was given to the ν₂ and ν₅ spectra which showed the effect of Coriolis resonance. By transferring some of the constants involved from the laser-Stark spectra we determined B₅^*, B₂^*, and q₅^* for CD₃Cl. The large effective q₅ constant permitted observation of the direct l-doubling transitions of high J. The analysis of the CH₃Cl spectra was much less complete than that on CD₃Cl because of limited data. The B rotational constants obtained were compared with the previous microwave and infrared results when available.By using the infrared data on ν₁ and ν₄ we evaluated the equilibrium B_e constants (α₄^B of CD₃³⁷Cl was estimated), and refined the equilibrium structure of methyl chloride reported by Duncan.     

The microwave spectrum of trifluoroacetonitrile in excited vibrational states

The microwave transitions J → J + 1 have been observed in the symmetric top molecule trifluoroacetonitrile, CF₃CN, for molecules excited into several of the low-lying vibrational states. Measurements made in the degenerate states v₇ = 1 v₈ = 1 have been fitted to the formula derived by Grenier-Besson and Amat (1) for transitions J → J + 1 in degenerate vibrational states of molecules with C_3v symmetry. The measurements for the state v₈ = 1 have been extended to 150 GHz where it is shown that the above formula becomes inadequate to describe accurately the observed spectrum.     

Microwave spectrum of methyl fluoride in excited vibrational states: Coriolis interaction and anomalous l-doubling transitions

The microwave spectrum of CD₃F in the v₂ = 1, v₃ = 1, v₅ = 1, and v₆ = 1 states was observed, including the direct l-doubling transitions in the v₅ = 1 and v₆ = 1 states. The Coriolis interaction between the v₂ = 1 and v₅ = 1 states was analyzed in detail. An anomaly in the Stark effect was noticed in some of the direct l-doubling transitions in the v₆ = 1 states, and was explained in terms of accidental degeneracy between the Kl₅ = 1 and the Kl₅ = ? 2 levels. Molecular constants associated with the vibrational and rotational motions were determined through an analysis of these spectra.The J = 1 ← 0 transitions of ¹²CH₃F in the v₂ = 1, v₃ = 1, v₅ = 1, and v₆ = 1 states and of ¹³CH₃F in the v₃ = 1 and v₆ = 1 states were observed, as well as the direct l-doubling transitions of ¹²CH₃F in the v₅ = 1 state. A preliminary analysis was carried out on the strong Coriolis interaction between the v₂ = 1 and v₅ = 1 states.     

The microwave spectrum of cyanoacetylene in ground and excited vibrational states

Microwave transitions are reported for ten isotopic species of cyanoacetylene in the ground, v ₄, v ₆, v ₆ and v ₇ vibrational states in the region 26·5-40·0 GHz. In addition millimetre-wave transitions of HCCCN and DCCCN in the ground v ₅, v ₆ and v ₇ vibrational states in the region 54·5-211·8 GHz have been measured. The combined data have been analysed to yield B_v, D_v, γ_rs, γ_ltlt′ and q_t vibration-rotation parameters, for HCCCN and DCCCN.

In addition millimetre-wave measurements pertaining to the v ₆ + v ₇ and v ₅ + v ₇ vibrational states have been analysed to give values for r_tt′J and approximate values of g_tt′ and r_tt′ (t = 5, 6; t′ = 7).

Rotational constants B_v in the first excited state of the fundamental vibrations v ₄, v ₅, v ₆ and v ₇ are combined with infra-red values for v ₁, v ₂ and v ₃ to give B_e for both HCCCN and DCCCN.     

The microwave spectrum of BrF5 in excited vibrational states: Coriolis interaction and an A1-A2 splitting of |akℓ|a ≠ 1 levels

The results of a numerical diagonalization treatment of the ν₅(B₁)-ν₉(E) Coriolis resonance in BrF₅ are presented. It is shown that the resonance is responsible for an A₁-A₂ splitting of the k? = ?3 lines in the v₉ = 1 state spectrum and of the |ak|a = 2 lines in the v₅ = 1 state spectrum. Assuming the sign of the constant R₆ is correctly known for BrF₅, the analysis of the Coriolis resonance provides the magnitudes and the signs of both the l-doubling constants q⁺ and $\text{q}{}^{\mathrm{?1}}$.     

Microwave spectrum of dimethylallene excited states and strong Coriolis coupling

The rotational spectra of six excited vibrational states of dimethylallene were measured and assigned to the corresponding vibrational levels, and for three more excited state spectra at least the rotational constants could be determined. Between the two lowest excited levels of symmetry species b₂ and b₁ of group C_2v a strong a-type Coriolis coupling was found to exist. The evaluation of the resulting perturbation by a diagonalization of the energy matrix yielded ζ^(a) = 0.36 and a precise value for the vibrational energy difference 48.761 GHz (1.6 cm^?1). The state b₂ is believed to be the first excited torsional substate (01, 10)₁ of methyl internal rotation, and the rotational transitions of this state as well as those of the strongly coupled state b₁ presented very irregular multiplet splittings. On the other hand, the splittings of the next-higher excited state of species a₂ which could be identified as the partner torsional substate (01, 10)₂, followed the regular pattern, yielding an internal rotation barrier V₃ (2079 cal/mole) not unlike that derived earlier from ground state splittings.     

The microwave spectra and vibration-rotation interaction constants for CD3I in the excited vibrational states

The microwave spectra in the J = 1 → 3 region for CD₃I has been observed and six excited vibrational states assigned. The vibration rotation interaction constants, α^B and nuclear quadrupole coupling constants, eQq, have been determined for the states: ν₂, ν₃, ν₅, ν₆, 2ν₃, and ν₃ + ν₆. For the degenerate vibrational states, the l type doubling constants, q_t were determined.     

Microwave spectrum of methylene fluoride in excited vibrational states

The rotational spectra of ¹²CH₂F₂ in seven of the nine fundamental vibrational states and also in overtone and combination states involving the ν₄ mode were observed and assigned. Coriolis interactions between ν₃ and ν₇, ν₂ and ν₈, ν₃ and ν₉, and ν₅ and ν₇ were analyzed by using approximate expressions for the rotational levels. An effective Hamiltonian with the Coriolis term in the off-diagonal block was applied to stronger interaction between ν₃ and ν₉. Fermi resonance between ν₃ and 2ν₄ was found to be negligible. The ground state spectra of ¹²CH₂F₂ and of ¹³CH₂F₂ were remeasured to improve the accuracy of the rotational and centrifugal distortion constants. The Coriolis coupling constants and the energy differences between two vibrational levels in resonance, which were obtained through an analysis of the satellite spectra, are compared with the results derived from a normal coordinate analysis.     

Submillimeter rotational spectrum of the formamide molecule: Ground and first excited vibrational states

The results of a study of the submillimeter rotational spectrum of formamide in states v_T=0 and 1 at frequencies of 290–500 GHz are presented. More than 300 transition frequencies are identified. Watson Hamiltonian constants are obtained for both states.Radio-Astronomy Institute, Academy of Sciences of Ukraine. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 37, No. 2, pp. 259–264, February, 1994.     

Millimeterwave spectrum of DC discharge produced ICN in excited vibrational states

An indigenously built 50 kHz source-modulated millimeter-wave spectrometer was used to produce cyanogen iodide (ICN) in the excited vibrational states (01¹0), (03³0), (10⁰0), (20⁰0) and (02⁰0) and record their corresponding rotational spectra. The analysis of the recorded spectra was carried out in the frequency range of 57.0–98.0 GHz. ICN was produced using a DC glow discharge through a mixture of methyl iodide (CH₃I) and benzyl cyanide (C₆H₅CH₂CN) vapor at low pressure. ¹²⁷I nuclear quadrupole hyperfine structure and the l-type doublet spectra of (01¹0) state have been resolved. The observed and assigned rotational transition frequencies were used in a least-square fit to determine more accurate values of molecular constants. The agreement between the derived parameters and those reported earlier clearly indicate that the reported spectral lines belong to ICN in the excited vibrational states. It also indicates that ICN could be produced in selective excited vibrational states by DC glow discharge technique.     

Microwave spectrum of sulfur difluoride in the first excited vibrational states vibrational potential function and equilibrium structure

Microwave spectra of SF₂ in the first excited states of the three normal modes were observed and analyzed. A comparison of the observed inertia defects in the ν₁ and ν₃ states with those calculated by omitting the contributions of the Coriolis interaction between the two modes led to a $\text{ν}\text{?}{}_1\text{-}\text{ν}\text{?}{}_3$ vibrational frequency differences of 25.72 ± 0.33 cm^?1, with ν₁ being definitely higher. The inertia defect in the ground state and our measured values for the inertia defect in the ν₂ state and for the $\text{ν}\text{?}{}_1\text{-}\text{ν}\text{?}{}_3$ difference were combined with the centrifugal distortion constants of Kirchhoff et al. [J. Mol. Spectrosc.48, 157–164 (1973)] to improve the harmonic force field. The interaction constant between the two SF stretching coordinates was determined precisely. The third-order and the cubic anharmonic potential constants were calculated from the observed vibration-rotation constants. The equilibrium structure was determined to be $\text{r}{}_{\mathrm{e}}\text{(}\text{SF}\text{) = 1.58745 ± 0.00012}\text{A}\text{?}$ and θ_e(FSF) = 98.048 ± 0.013°.     

Microwave spectrum of nitrogen dioxide in excited vibrational states—Equilibrium structure

Microwave spectra were observed for ¹⁴NO₂ in the vibrationally excited ν₁, ν₂, ν₃, and 2ν₂ states, as well as for ¹⁵NO₂ in the ν₁ and ν₂ states. The rotational constants, spin-rotation coupling constants and hyperfine interaction constants were precisely determined. Second-order change of the spin-rotation coupling constants with respect to the bending vibrational quantum number v₂ was also determined. Combined use of the rotational constants obtained by the present microwave investigation and those reported in high-resolution infrared spectroscopic studies leads to the determination of all the vibration-rotation interaction constants α_s and γ_ss′ and the equilibrium structure of nitrogen dioxide, $\text{r}{}_{\mathrm{<mtext>e</mtext>}}\text{(}\text{N}\text{O) = 1.19389 ± 0.00004}\text{A}\text{?}$ and θ_e (ONO) = 133°51.4′ ± 0.2′, in the second-order approximation with respect to the vibrational quantum numbers.     

The rotational spectrum of acrylonitrile in excited states of the two low-frequency CCN bending vibrational modes

The strongest vibrational satellites in the rotational spectrum of acrylonitrile have been assigned and frequencies of μ_a- and μ_b-type transitions in the frequency range 27–184 GHz are reported for the first two excited states in the lowest frequency in-plane CCN bending vibrational mode and the first excited state in the out-of-plane CCN bending mode. The values of the rotational constants, the quartic and sextic centrifugal distortion constants, and one octic centrifugal distortion constant are determined for each of these states. Less extensive results are also presented for the third quantum of the in-plane bend. The data set for the ground state has been extended by a number of new measurements and the improved ground state constants are used in a discussion of changes in rotational and centrifugal distortion constants with vibrational state where all constants associated with P_zⁿ and P²P_z⁽ⁿ⁻²⁾ terms in the Hamiltonian are found to reflect the common origin of the two CCN bends.     

Millimeter and submillimeter wave rotational spectrum of pyridine in the ground and excited vibrational states

The pure rotational spectra of the ground and five excited vibrational states of pyridine were measured, assigned and fit in the 75-110 and 260-370 GHz frequency bands. An improved set of spectroscopic constants was obtained for the ground state, and all the rotational and quartic centrifugal distortion constants were obtained for the excited vibrational states.     

Millimeter wave rotational spectrum of deuterofulminic acid,DCNO, in excited vibrational states

Rotational transitions of DCNO in the vibrational states 00002, 00003, 00020, and 00011 have been measured and analyzed. These results complete the presentation of assigned millimeter wave transitions of DCNO.The analysis of rotational l-type resonance in the 00002 and 00020 states is more satisfactory in the case of DCNO than in that of HCNO due to the absence of accidental resonances. The values obtained for the vibrational anharmonicity constant g₅₅ for 00002 and 00003 agree within experimental error with those found from the vibrational spectrum.An ambiguity in the assignment of the symmetry of the transitions in the four components of the 00011 vibrational state is discussed.     

The millimeter-wave spectra of germyl fluoride in excited vibrational states

Millimeter-wave spectra of GeH₃F in the v₃ = 1, v₆ = 1, v₂ = 1, and v₅ = 1 excited states have been recorded. Strong Coriolis resonance between the v₂ = 1 and v₅ = 1 states results in a highly perturbed spectrum which shows no obvious resemblance to the normal symmetric top excited state pattern. A similar, but not so strong coupling, exists between the v₃ = 1 and v₆ = 1 states. These spectra are analyzed by setting up the Coriolis coupled Hamiltonian matrices for these states. It has been shown that the apparently anomalous distortion constants of these states are due to the Coriolis coupling and the distortion parameters obtained with the model presented are, as expected, close to the ground state values.     

Submillimeter-wave spectroscopy of HCO in the excited vibrational states

The pure rotational transitions of HCO⁺ in excited vibrational states located below 5000 cm⁻¹ over the ground state have been investigated with a high-sensitivity frequency/magnetic field double modulation submillimeter-wave spectrometer in the frequency range of 280-810 GHz. The ions were generated in an extended negative glow discharge through a gas mixture of a few millitorrs of H₂ and CO and 12 mTorr of Ar buffer gas. Throughout the experiments, the cell was maintained at liquid nitrogen temperature. In the present study, we have determined accurate molecular constants for the excited vibrational states. Our analysis suggests that there may be a higher order Coriolis interaction between the (0 3 1) and (1 2 0) states. In previous investigations, the Stark effect caused by the electric field present in the discharge plasma was cited as a reason for non-observations of low-J lines in the (02²0) and for the systematic shifts observed for low-J lines in the (01¹0), (02²0), (03¹0), and (04²0) states of HCO⁺ as well as DCO⁺. In the present investigation, some low-J lines in the (02²0) and (04²0) states have been observed in emission. Furthermore, J = 8-7, J = 9-8 lines in (03^1e1) were detected in emission. This finding indicates that missing low-J lines for the Δ sublevel obtained in the past is not due to the Stark effect but due to small population differences in those levels.     

The infrared spectrum of C3O2: The interaction between ν7 and the ν2 and ν4 vibrations

The 3ν¹₇, 3ν³₇, and 4ν⁰₇ hot bands of the ν₄ fundamental of C₃O₂ in the 1580 cm^?1 region were analyzed from tunable diode laser spectra and the ground state to ν₄ + 2ν⁰₇ band at 1644 cm^?1 from Fourier transform spectra (FTS). The molecular constants for all of the v₄ 1 ← 0 bands as well as the intensity of the ν₀ + 2ν⁰₇ sum band relative to the ν₄ fundamental were in agreement with the predictions of the model of Weber and Ford. FTS spectra at 0.05 cm^?1 resolution were obtained of the sum and difference bands of ν₂ with ν₇ in the 750–900 cm^?1 region. Sharp Q branches occur for each ν₇ state in the sum bands, but only a number of R-branch bandheads and no recognizable Q branches in the difference bands. Assignments of the sum band Q branches through v₇ = 6 were made and molecular constants were determined for the ν₂ + ν¹₇ ← 0 transition at 819.7 cm^?1. The ν₇ potential function in the v₂ = 1 state was found to have a 1.2 cm^?1 barrier with a minimum at α = 4.9°, where 2α is the angular deviation from linearity. The Q-branch positions predicted from the calculated energy levels fit those observed within several cm^?1.     

Microwave spectrum of dimethylketene: Centrifugal distortion and Coriolis interaction

For the prolate asymmetric (κ = ?0.58) top molecule dimethylketene the centrifugal constants have been determined in terms of the Δ constants by means of ΔK_? ≠ 0 rotational transitions. Two earlier assigned torsional excited states (01, 10)₁ and (01, 10)₂ of symmetry B₂ and A₂ of C_2v could be confirmed. A third fundamental vibration v_r(b₁), probably the inplane skeletal rock, has been found and analyzed in the v_r = 1 and v_r = 2 states. The variation of the centrifugal constants and of the inertial defects with the state of excitation could be explained by Coriolis coupling between the v_r(b₁) = 1 vibrational and v_t(b₂) = 1 torsional excited states. The Coriolis constant $\text{ζ}{}_{\mathrm{rt}}{}^{\mathrm{a}}$ and the torsional frequency ω_t(b₂) have been estimated to be $\text{ζ}{}_{\mathrm{rt}}{}^{\mathrm{a}}\text{≈ 0.24}$ and ω_r(b₁) - ω_t(b₂) ≈ 5.8 cm^?1, respectively.