ℓ-Resonance effects in C2H2 near 13.7 μm. Part H: The two quantum hotbands

This article is the second part on ℓ-resonance effects on the rotation-vibration bands of acetylene observed in the ν₅ fundamental region. While the first part concentrated on the energy level analysis of the fundamental and the seven strongest hotbands originating in the ν₄ and ν₅ excited states for both major isotopes [Spectrochim. Acta 48A, 1203 (1992)], this article summarizes the results of the analysis of the hotbands 2ν₄ + ν₅ ← 2ν₄, ν₄ + 2ν₅ ← ν₄ + ν₅, and 3ν₅ ← 2ν₅ from which improved molecular constants for the 2ν₄ and three quantum energy levels were derived for the major isotope ¹²C₂H₂. The mixing levels within the excited vibrational states due to vibrational and rotational ℓ-resonance effects are discussed which lead to the identification of the strong “forbidden” Δℓ3 band, 2ν₄+ ν³₅←2ν^Oe₄ as a result of ℓ-resonance intensity perturbation.     

High resolution infrared analyses of fundamentals and overtones in isotopic ketenes

Rovibrational structure in the ν₅, ν₆, ν₇, ν₈ fundamentals and 2ν₅, 2ν₆ overtones in each of H₂¹²C¹²CO, H₂¹²C¹³CO, H₂¹³C¹²CO has been assigned and analysed. The effects of Fermi resonance between ν₇ and ν₂+ν₈ are corrected for, and a set of accurate unperturbed vibrational frequencies and ¹³C isotopic frequency shifts therefrom is obtained. The changing effects of the major Coriolis interactions involving the out-of-plane fundamentals, ν₅ and ν₆, are manifest in varying isotopic displacements of equivalent Q branch structures between the isotopic species studied, from which accurate isotopic vibrational shifts are obtained. Variable anharmonicity constants associated with the vibration frequencies of 2ν₅ and 2ν₆ give evidence of major Fermi resonance interactions between both overtones and the ν₄ fundamental, which they straddle.     

Vibrational levels and anharmonicity in SF6—I. Vibrational band analysis

The vibrational spectrum of SF₆ has been recorded with a Fourier-transform i.r. spectrometer at a resolution of 0.05 cm⁻¹ and pressure—path length products of up to 2 × 10⁵ Torr-cm. Twenty-nine bands were observed. Rotational structure was resolved for 11 of these and polynomials were fitted to the observed frequencies to yield the scalar spectroscopic constants, including the band origins m and derived values of B′B₀ and the Coriolis constants ζ. For 12 other unresolved bands accurate estimates of the origins could be made from the frequency of a sharp Q-branch edge. Three more bands (ν₃, 2ν₁ + ν₃, and 3ν₃) were not resolvable at our resolution but have been previously analyzed from Doppler-limited or sub-Doppler spectra. In addition, about 10 assignable hot bands were observed whose frequency shifts relative to the principal transitions could be accurately measured; two of these were sufficiently resolved for full scalar analyses. These frequencies were combined with results of several high-resolution Raman studies by other authors to yield the most complete data set on SF₆ vibrational levels yet obtained. Isotopic frequency shifts have also been measured. The effective Coriolis constants for combination and overtone bands of octahedral molecules are discussed.     

Vibrational spectra and force constants of symmetric tops—XXIV. Vibrational and rotational analysis of parallel overtones and combination bands of CF3Br

The i.r. spectra of monoisotopic CF₃⁷⁹Br and of natural CF₃Br have been investigated in the gas phase with a resolution of ∼ 0.04 cm⁻¹. The rotational J structure of 2ν₁, 2ν₃, ν₁ - ν₃, ν₁ + ν₃, ν₁ + ν₂, ν₂ + 2ν₃ and 2ν₂ + ν₃ of CF₃⁷⁹Br has been resolved, Furthermore vibrational transitions of hot bands and of further parallel bands have been measured. Numerous excited state molecular parameters ν⁰_i, x_ij, α^A_i and α^B_i have been determined. Due to the accidental equivalence of ν₁/2ν₅ and ν₂ + ν₃, strong anharmonic resonance correlates all (n + 2)ν₃/ν₁ + (n - 1)ν₃/2ν₅(∥)+(n - 1)ν₃/ν₂ + nν₃ levels.     

ℓ-Resonance effects in the νv5, 2ν5←ν5, and ν4 + ν5←ν4 bands of C2H2 and 13C12CH2 near 13.7 μm

An extension to the previous LSCD (lower state combination difference) determination of molecular parameters involving acetylene's ν₅ fundamental and the strongest one quantum hotbands, 2ν₅←ν₅ and ν₄ + ν₅←ν₄ [J. Molec. Spectrosc. 146, 389 (1991)] has been made. A novel iterative numerical diagonalization procedure was employed to fit the vibrational states involved in the seven one quantum hotbands. This method utilizes the Hellmann—Feynman theorem to calculate first derivatives and singular value decomposition (SVD) in its least-square procedure and permits the simultaneous evaluation of the effective dipole moment responsible for the ℓ-type resonance effect upon IR intensities. A set of molecular parameters describing the rotation—vibration levels of the ground state, ν₅, ν₄, 2ν₅ and ν₄ + ν₅ for the major isotope and for ¹³C¹²CH₂ are reported based upon FT-spectrometric data taken at the McMath Solar Telescope Observatory. The improved spectroscopic parameters retrieved from this investigation will serve as a database for modelling abundances of acetylene in various astrophysical sources.     

Ir absorption spectrum of CrO2Cl2 molecules for high-lying states of the vibrational quasi-continuum

A new approach to the spectroscopy of highly excited vibrational states of polyatomic molecules has been elaborated. The molecules of CrO₂Cl₂ were prepared in states with a vibrational energy of the ground electronic term A₁ of ≈ 19000 cm⁻¹ by means of internal conversion of electronic energy from the electronic state B₁ excited by laser radiation. The spectroscopy of the vibrationally excited molecules has been carried out in the region of the ν₆ and ν₁ bands with diode and CO₂ lasers. The fwhm of the obtained spectrum was ≈ 15 cm⁻¹. The intermode interaction in CrO₂Cl₂ has been theoretically analyzed, and the calculated spectrum compared with that measured experimentally. The time evolution of the spectrum of vibrationally excited CrO₂Cl₂ molecules has been studied. The average energy transferred per one collision with unexcited CrO₂Cl₂ molecules was equal to 〈δE〉 ≈ 1200 cm⁻¹.     

High-resolution infrared analysis of the ν17 band of pyridine

A method for analyzing asymmetric top rovibrational bands displaying both blended and resolved features is described. The two-phase computational procedure uses a modified version of the asymmetric rotor-band contour program FASTPLOT to generate a preliminary set of upperstate spectroscopic constants. The parameters are subsequently refined by employing the assigned line-fitting formalism of the ASYROT program using both resolved and blended features. The technique is detailed in a comprehensive analysis of the ν₁₇ band of pyridine. Inclusion of quartic centrifugal distortion constants was found to satisfactorily model a high-resolution (0.004 cm^?1) spectrum of this band, yielding a standard deviation of 0.00137 cm^?1. The variation in the rotational parameters with vibrational quantum number is examined in terms of possible weak rovibrational perturbations to the ν₁₇ state. An ab initio calculation of the ν₁₇/ν₂₇ Coriolis coupling constant indicates the observed results are consistent with the interaction of these two vibrational states.     

Evidence for the 2ν3 overtone in the infrared spectrum of methyl chloride

It is shown that the P_Q1 branch of the ν₅ fundamental of CH₃³⁵Cl appears to be split because of a vibration-rotation interaction between ν₅ and 2ν₃, with eventual level crossing in the J structure. This interaction is due to the indirect coupling of ν₅ and 2ν₃ through common intermediate levels, and especially to the cubic anharmonic coupling of 2ν₃ and ν₂ and x, y Coriolis coupling of ν₂ and ν₅. This explanation has been verified by the computer simulation of band contours, and an estimate of the 2ν₃ band origin is given.     

Lifetimes of C-2 in rotational levels of the B̃2Σ+u state in the gas phase

Lifetimes of C^-₂ in rotational levels of the B?²Σ⁺_u:ν′ = 0, ν′ = 1 states have been measured. C^-₂ was produced from bromoacetylene and rare-gas metastables and the B?²Σ⁺_u—X?²Σ⁺_g transition was laser excited. The lifetimes are constant within a vibrational level, 77 = 8 ns for ν′= 0 and 73 = 7 ns for ν′ = 1. The oscillator strength f_νo = 0.044 ± 0.004.     

Microwave spectra of the ground and excited vibrational states of isotopic species of nitroethylene

Rotational spectra of nitroethylene, four deuterium and six ¹³C species have been measured and analysed in the frequency range from 8 to 26 GHz. Rotational transitions in the ground state, in progressions of excited states of the NO₂ torsional mode ν₁₈, in the in-plane skeletal bending mode ν₁₃, and in doubly excited states σ₁₃+ν₁₃+ν₁₈ν₁₈ could be assigned for nitroethylene and its deuterated species. The spectra of the ¹³C isotopic species were observed in natural abundance and their assignments have partly been checked by microwave — microwave (mw — mw) double resonance. All the spectra in each of the different vibrationally excited states were found to acceptably obey a rigid rotor pattern with centrifugal distortion, corresponding to a high barrier for the NO₂ internal rotation. Rotational constants and inertia defects all show the same qualitative dependence on the internal state. The ground state rotational constants of all isotopic species have been used to determine a refined molecular structure.     

Rovibrational study of the ν2 + ν±14, ν2 + 3ν±16, ν1 + ν±15, ν±14 + ν±15, ν±14 + ν±5, ν±5 + 3ν±16, ν±5 + 3ν±36 and ν1 + ν2 infrared bands of CH335Cl studied in a high-resolution FTIR spectrum from 4250 to 4600 cm−1

About 6400 lines belonging to the ν₂ + ν^±1₄, ν₂ + 3ν^±1₆, ν₁ + ν^±1₅, ν^±1₄ + ν^±1₅, ν^±1₄ + ν^±₅, ν^±₅ + 3ν^±1₆ and ν^±₅ + 3ν^±3₆ bands have been assigned. An r.m.s. deviation of 0.047 cm⁻¹ has been achieved by a least-squares fit of 1427 lines. For this purpose, a simplified model, taking into account five anharmonic resonances already found in a previous work [Molec. Phys. 70, 849 (1990)] and the well known x-y Coriolis resonance between the ν₂ and ν₅ modes of methyl halides, was used. Although not observed, the ν^±1₄ + ν^±1₅ and ν₁+ ν₂ parallel bands are strongly coupled by Coriolis resonance to ν₂ + ν^±1₄ and ν^±1₅ respectively. A few secondary resonances remain unexplained in several parts of the spectrum.     

New analysis of the 2ν4, ν4+ν6, 2ν6, ν3+ν4, ν3+ν6, ν1, ν5, ν2+ν4, 2ν3, ν2+ν6 and ν2+ν3 bands of formaldehyde H212C16O: Line positions and intensities in the 3.5 μm spectral region

This work is mainly motivated by the atmospheric importance of formaldehyde. The 3.5 μm region is indeed commonly used for the infrared detection of this molecule in the troposphere and the line parameters which are presently available in the atmospheric databases for H₂CO are of rather poor quality in this spectral range. Using New Fourier transform spectra recorded in LPMA and in GSMA it has been possible to perform an extensive study of the 2ν₄, ν₄+ν₆, 2ν₆, ν₃+ν₄, ν₃+ν₆, ν₁, ν₅, ν₂+ν_4, 2ν₃, ν₂+ν₆ and ν₂+ν₃ bands of formaldehyde. Combining these data with previous frequency and intensity measurements for the ν₃+ν_4, ν₃+ν₆, ν₁, ν_5, ν₂+ν_4, 2ν₃ and ν₂+ν₆ bands [L.R. Brown R.H. Toth and A.S. Pine J. Mol. Spectosc. 406–428 and references therein] and an adequate theoretical model, it proved possible to reproduce rather satisfactorily the experimental data and to generate a list of line positions and intensities for the 3.5 μm region. The Hamiltonian model accounts for the various Coriolis-type resonances and anharmonic resonances which perturb the energy levels of the 4², 4¹6¹, 6², 3¹4¹, 3¹6¹, 1¹, 5¹, 2¹4¹, 3², 2¹6¹, and 2¹3¹ vibrational states. This is also the case for the line intensity calculations, which allow one to reproduce satisfactorily the line-by-line intensity measurements as well as the integrated intensities available in the literature.     

High-resolution spectroscopy on the B2Σ+,ν' = 0→X2Π, ν″ =1 transition in SiCl

High-resolution laser-induced fluorescence spectra of²⁸Si³⁵Cl and ²⁸Si³⁷Cl have been observed in a molecular beam. Accurate constants describing the rotational structure in the X ²Π, ν″ = 1 as well as in the electronically excited B ²Σ⁺, ν' = 0 state are given. An inverted fine structure was found in the excited state with a spin-splitting constant γ = −31.15±0.19 MHz for Si³⁵Cl and γ = −30.62 ±0.61 MHz for Si³⁷Cl.     

The i.r. rotation—vibration spectrum of CH3F in the region of 3000 cm−1

The i.r. spectrum of CH₃F has been remeasured with a resolution of about 0.04 cm⁻¹ from 2800 cm⁻¹ to 3160 cm⁻¹. There are four important vibrational transitions that contribute to the spectrum in this region and these have been identified as the two CH-stretching fundamentals, ν₁ and ν₄, the overtone of the E-type CH-deformation mode, 2ν₅, and the combination of the AI and E-type CH-deformation modes, ν₂ + ν₅. The spectrum shows evidence of a number of strong perturbations and we believe that we have identified a Fermi resonance between the states |υ₁ = > and |υ₅ = 2, l₅ = 0>, another Fermi resonance between the states |υ₄ = 1, l₄ = ± 1>; and |υ₂ = 1, υ₅ = 1, l₅ = ±1>; and Coriolis interactions between |υ₅ = 2, l₅, = 0> and |υ₂ = 1, υ₅ = 1, l₅ = ±1> and between |υ₁ = 1> and |υ₄ = 1, l₄ = ±1>. About 600 rotation-vibration transitions have been assigned and many of these have been analyzed to obtain effective rotational constants. The interpretation of the effective rotational constants is complicated by the strong perturbations but we believe that we have been able to estimate some of the unperturbed molecular parameters.     

Combination of the matrix isolation and the isotropic substitution techniques: Vibrational spectra and molecular constants of titanium tetrachloride and germanium tetrachloride

The i.r. spectra of titanium tetrachloride and germanium tetrachloride in argon matrices have been recorded in the region of the ν₃(F₂) fundamental. The same has been done for the samples ⁴⁸TiCl₄, Ti³⁵Cl₄, ⁷⁴GeCl₄ and Ge³⁵Cl₄. In this manner assignments could be made with a high order of certainty. The same region has been studied for the pure isotopic species ⁴⁸Ti³⁵Cl₄ and ⁴⁸Ti³⁵Cl₄, in the gas phase. Similarly, the spectra of the isotopically pure species of germanium tetrachloride, ⁷⁴Ge³⁵Cl₄ and ⁷⁴Ge³⁷Cl₄, and of the normal compound have been recorded in the gas phase for both the F₂ modes for which Coriolis coupling constants were calculated from the i.r. band contours. Using six independent isotopic shifts for titanium tetrachloride, four ζ-values and three isotopic shifts for germanium tetrachloride as additional data, force constants have been calculated. The force field for both molecules have much smaller error limits when compared with those previously reported.     

The rotational spectrum of the hydrogen-bonded heterodimer H2O…HF in the frequency range 40–80 GHz

The μ_a R-branch rotational spectra of the ground and first excited states of the three lowest vibrational modes of the H₂O…HF heterodimer have been observed in the frequency range 40–80 GHz. Coriolis perturbations between the ground vibrational state (υ = 0) and the first excited state of the out-of-plane bending vibration (υ_β(0) = 1) show that for a given J the K₋₁ = 2 levels of υ_β(0) = 1 lie approximately 3 cm⁻¹ above the K₋₁ = 3 levels of υ = 0. The vibrational separation between these two states is estimated to be 70±3 cm⁻¹. This value is consistent with those determined by other methods and reinforces the conclusion that ν_β(0) is governed by a double-minimum potential energy function with the quantitative form previously published. A perturbation is also observed in the first excited state of the hydrogen-bond stretching vibration υ_σ = 1. This manifests itself as a large, negative centrifugal distortion constant D_JK = −8.5 MHz compared with 2 MHz in the other vibrational states.     

Calculations of IR-spectra of metastable bond isomers of ruthenium nitrosocomplexes [Ru(NO)Cl<Subscript>5</Subscript>]<Superscript>2−</Superscript> [Ru(NO)(CN)<Subscript>5</Subscript>]<Superscript>2−</Superscript> by DFT method

IR-spectra of stable and metastable isomers of ruthenium nitrosocomplexes, [Ru(NO)Cl₅]^2? and [Ru(NO)(CN)₅]^2?, have been calculated within the frames of density functional theory. Frequency assignment was refined on the base of analysis of normal vibration in internal vibrational coordinates. Calculation results confirm that spectrally observed metastable states are bond isomers with ν¹-ON and ν²-NO coordination.     

FTIR spectra of the 2ν4, ν4 + ν6 and 2ν6 bands of formaldehyde

High resolution IR spectra of the overtones and the combination band of the ν₄ and ν₆ modes of formaldehyde (2ν₄, ν₄ + ν₆ and 2ν₆) were measured in the region of 2200–2650 cm⁻¹ using FTIR. The combination band ν₄ + ν₆, whose dipole transition is forbidden from molecular symmetry, was observed due to the intensity borrowed from the other bands. The observed frequencies were analysed by a Hamiltonian in which A-type Coriolis interactions and Darling—Dennison interaction were taken into account. The ratio and the relative signs of the transition dipole moments of the overtone bands, μ_2ν4 and μ_2ν6, have been determined by analysing the intensity distribution of the vibration—rotation lines.     

Vibrational spectra and force constants of symmetric tops—XLII. Rovibrational spectra of CF3I in the ν2, ν3, 2ν3 and ν2 + ν3 regions

The gas phase i.r. spectrum of CF₃I has been investigated in the ν₂, ν₃, 2ν₃ and ν₂ + ν₃ region with a resolution of 0.04 cm⁻¹. Rotational J clusters have been resolved, and several vibrational and rovibrational parameters of ν₂, 743.364(8) cm⁻¹ and ν₃, 286.303(3) cm⁻¹, have been determined by polynomial methods and by band contour simulation.     

Photoacoustic study of CH4(ν3) deactivation by collisions with rare gases

CH₄(ν₃) deactivation is studied in the gas phase by the photoacoustic method at 300 K. Rapid vibration-to-vibration transfer holds the adjacent levels in a quasi-equilibrium distribution. The vibrational levels can then be grouped in two sets: (ν₂, ν₄) on the one hand and (ν₃, ν₁, 2ν₂, 2ν₄, ν₂ + ν₄) on the other. By successive dilution of CH₄ in He, Ne, Ar, we determined the vibration-to-translation-rotation rate constants characterizing the deactivation of each set. The vibration-to-vibration intermolecular rate constant which connects the two sets is also obtained.