Analysis of the ν9/ν10 band system of allene

The infrared spectrum of allene has been recorded with high resolution (0.002-0.004 cm⁻¹) on a Fourier transform instrument in the region 730 to 1170 cm⁻¹ containing the perpendicular bands, ν₉ and ν₁₀. A total of 21 subbands with KΔK ranging from −6 to +14 have been assigned in the ν₉ band, and 26 subbands with KΔK = −10 to +15 have been assigned in the ν₁₀ band. The bands are affected by a combination of a J_z-Coriolis and a quartic anharmonic interaction between their upper states ν₉ and ν₁₀. In addition, several other more localized perturbations are found in the spectrum. The nature of the interactions responsible for these perturbations is discussed, and five of the strongest perturbations are quantitatively accounted for by constructing a Hamiltonian matrix which includes five different perturbing states and their Coriolis and anharmonic resonances with the ν₉ and ν₁₀ upper states. A set of spectroscopic constants for the ν₉ and ν₁₀ states and for some of the perturbing states is reported.     

Line Positions and Intensities of the ν1+ ν2+ 3ν3, ν2+ 4ν3, and 3ν1+ 2ν2Bands of Ozone

Using a Fourier transform spectrometer, we have recorded the spectra of ozone in the region of 4600 cm⁻¹, with a resolution of 0.008 cm⁻¹. The strongest absorption in this region is due to the ν₁+ ν₂+ 3ν₃band which is in Coriolis interaction with the ν₂+ 4ν₃band. We have been able to assign more than 1700 transitions for these two bands. To correctly reproduce the calculation of energy levels, it has been necessary to introduce the (320) state which strongly perturbs the (113) and (014) states through Coriolis- and Fermi-type resonances. Seventy transitions of the 3ν₁+ 2ν₂band have also been observed. The final fit on 926 energy levels withJ_max= 50 andK_max= 16 gives RMS = 3.1 × 10⁻³cm⁻¹and provides a satisfactory agreement of calculated and observed upper levels for most of the transitions. The following values for band centers are derived: ν₀(ν₁+ ν₂+ 3ν₃) = 4658.950 cm⁻¹, ν₀(3ν₁+ 2ν₂) = 4643.821 cm⁻¹, and ν₀(ν₂+ 4ν₃) = 4632.888 cm⁻¹. Line intensities have been measured and fitted, leading to the determination of transition moment parameters for the two bands ν₁+ ν₂+ 3ν₃and ν₂+ 4ν₃. Using these parameters we have obtained the following estimations for the integrated band intensities,S_V(ν₁+ ν₂+ 3ν₃) = 8.84 × 10⁻²²,S_V(ν₂+ 4ν₃) = 1.70 × 10⁻²², andS_V(3ν₁+ 2ν₂) = 0.49 × 10⁻²²cm⁻¹/molecule cm⁻²at 296 K, which correspond to a cutoff of 10⁻²⁶cm⁻¹/molecule cm⁻².     

High-Resolution Infrared Spectroscopy of Methyl Isocyanide: The ν3, ν6, and ν7 + ν8 Bands

The vibration-rotation spectrum of methyl isocyanide (CH₃NC) has been recorded with the aid of a high-resolution Fourier transform spectrometer in the region 1370 to 1560 cm⁻¹ containing the perpendicular band of the fundamental vibration ν₆ (species E), the weaker parallel band of the ν₃ (A₁) fundamental, and the perpendicular combination band ν₇ + ν₈ (E) enhanced by Fermi resonance with ν₆. Sixteen hundred seventy well-resolved lines were assigned to 15 subbands of ν₆, 6 subbands of ν₃, and 3 subbands of ν⁻₇ + ν⁻₈. A strong x, y-Coriolis resonance between ν₃ and ν₆ and Fermi resonance between ν^±₆ and the E component ν₇ + ν₈, as well as between ν₃ and the A_1,2 components ν^±₇ + ν₈, greatly affects the spectrum. Additional weaker anharmonic interaction of ν₆ with the ν₄ + 2ν²₈ combination and higher-order rotational interactions connecting the various states were also detected in the spectrum. All of these interactions have been incorporated into a 9 × 9 Hamiltonian matrix used for modeling the upper states of the observed transitions. A set of spectroscopic constants is reported for the upper states of the bands ν₃, ν₆, and ν₇ + ν₈ and for ν₄ + 2ν²₈ which reproduces the observed lines with an overall standard deviation of 0.0012 cm⁻¹.     

The ν1 and ν3 stretching fundamental bands of PD3

The infrared (IR) spectrum of PD₃ has been recorded in the 1580–1800 cm⁻¹ range at a resolution of 0.0027 cm⁻¹. About 2400 rovibrational transitions with J^′=K^′22 have been measured and assigned to the ν₁ (A₁) and ν₃ (E) stretching fundamentals. These include 506 “perturbation-allowed” transitions with selection rules Δ(k−l)=±3. Splittings of the K^′′=3 lines have been observed. Effects of strong perturbations are evident in the spectrum. Therefore the rovibrational Hamiltonian adopted for the analysis explicitly takes into account the Coriolis and k-type interactions between the v₁=1 and v₃=1 states, and includes also several essential resonances within these states. The rotational structure in the v₁=1 and v₃=1 vibrational states up to J^′=K^′=18 was reproduced by fitting simultaneously all experimental data. Thirty-four parameters reproduced 1950 transitions retained in the final cycle with a standard deviation of the fit equal to 4.9 × 10⁻⁴ cm⁻¹ (about the precision of the experimental measurements).     

Millimeter-Wave and High-Resolution Infrared Spectra of Monoisotopic SCSe: Equilibrium, Ground State, and ν1, mν2, and nν3 Rovibrational Parameters

The Fourier transform infrared spectrum of monoisotopic SC⁸⁰Se has been investigated in the ν₂, ν₃, 2ν₂, 2ν₃, and ν₁ regions with a resolution between 3 and 4 × 10⁻³ cm⁻¹. In addition, the millimeter-wave spectrum has been studied in the region 150 to 320 GHz, and ground and ν₂ = 1 excited state transitions have been measured. Ground state constants, B₀ = 2043.285 4(4) MHz and D₀ = 146.53(5) Hz, have been determined from a merge of millimeter-wave data and ground state combination differences spanning J values up to 77 and 143, respectively. The band centers ν₂ = 352.341 075(9) cm⁻¹ and ν₃ = 505.480 06(5)cm⁻¹ have been determined. The rovibrational parameters of numerous overtone and combination levels (ν₁ν^l2₂ν₃) = 02⁰0, 02²0, 03¹0, 03³0, 04⁰0, 04²0, 00⁰2, and 00⁰3 have been obtained from polynomial analyses whose standard deviations ranged from 0.7 to 3.5 × 10⁻⁴ cm⁻¹. The 10⁰0 level, ν_eff 1435.840 cm⁻¹, is anharmonically perturbed by the 04⁰0 level, with an avoided crossing at J = 55, and W₁₂₂₂₂ = 0.963 09(1) cm⁻¹. Transitions to both the upper (E⁺) and lower (E⁻) sublevels of the dyad were observed for 1 ≤ J′ ≤ 117 and 4 ≤ J′ ≤ 171, respectively, and the deperturbed wavenumbers ν₁ = 1435.542 76(2) and 4ν⁰₂ = 1432.725 00(3) cm⁻¹ were derived. Furthermore, a local crossing of the E⁻ and 04²0 levels involving l-type resonance was observed at J = 91.     

Line Intensities in the ν1, ν3, and 2ν2 Bands of H2Se

Using a high-resolution Fourier transform spectrum of hydrogen selenide in natural abundance, about 600 intensities of lines belonging to the ν₁, ν₃, and 2ν₂ bands of H₂⁸⁰Se were measured. A least-squares fit of these intensities was performed, allowing determination of the vibrational transition moments of these bands and their rotational corrections. Finally, the first derivatives of the dipole moment with respect to the normal coordinates q₁ and q₃ were found to be ∂μ_χ/∂q₁ = (−0.5938 ± 0.010) × 10⁻¹ and ∂μ_z/∂q₃ = (0.5683 ± 0.010) × 10⁻¹ Debye, respectively.     

High-resolution infrared spectra of HCF3 in the ν6 (500 cm) and 2ν6 (1000 cm) regions: rovibrational analysis and accurate determination of the ground state constants C0 and DK

The high-resolution infrared spectrum of HCF₃ was studied in the ν₆ fundamental (near 500 cm⁻¹) and in the 2ν₆ overtones (near 1000 cm⁻¹) regions. The present study reports on the analysis of the hot bands in the ν₆ region, as well as the first observation and assignment of the 2ν₆² perpendicular band. Using ν₆, 2ν₆^±2–ν₆^±1 and 2ν₆² experimental wavenumbers, accurate coefficients C₀ and D_K⁰ of the K-dependent ground-state energy terms were obtained, using the so-called “loop method.” Ground-state energy differences Δ(K,J)=E₀(K,J)−E₀(K−3,J) were obtained for K=3–30. A least-squares fit of 81 such differences gave the following results (in cm⁻¹): C₀=0.1892550(15); D_K⁰=2.779(26) × 10⁻⁷.     

The 2ν8 Band of CH3CN

The overtone band 2ν⁰₈ of CH₃CN around 720 cm⁻¹ has been measured on a Bruker Fourier transform spectrometer at a resolution of 0.003 cm⁻¹. Only the parallel band was observed, but due to the l(2, 2) resonance, ΔK = −2 lines leading to the v₈ = 2, l₈ = −2 levels with K = 1-3 could be seen. More information for the l₈ = ±2 component of the vibrational state v₈ = 2 was evaluated from the hot band 2ν^±2₈ - ν^±1₈. Altogether more than 1000 lines were assigned. In the fit pure rotational lines from literature were also combined. Among the results the anomalous A₀ - A′ values 4.6722(13) × 10⁻³ cm⁻¹ for the 2ν⁰₈ band and 7.0324(32) × 10⁻³ cm⁻¹ for the 2ν^±2₈ band are striking.     

High resolution FTIR spectroscopy of pentafluoroethane: perturbations in the Coriolis doublet of ν4 and ν13

The FTIR spectrum of pentafluoroethane (R125) was measured in the mid infrared region from 900 to 4000 cm⁻¹. Vibrational assignments for R125 are revised by comparison of previous and current experimental data with ab initio calculations at both the MP2/6-311+(d,p) and B3LYP/TZV+(3df,3p) levels of theory. High resolution FTIR spectra were recorded at room temperature and in an enclosive flow cell at a rotational temperature of 140 K. The cold spectrum was sufficiently resolved to enable rovibrational analyses of the overlapping ν₄ (1200.7341 cm⁻¹) and ν₁₃ (1223.3 cm⁻¹) bands, which have a/c hybrid and b-type character, respectively. Ground state combination differences were used to confirm assignment of 2375 lines to ν₄ (J_max = 86, K_{a max} = 50) and 2921 lines to ν₁₃ (J_max = 60, K_{a max} = 54). Effective rotational and centrifugal distortion constants were determined for ν₄, and the polarization ratio was found to be . Severe Coriolis perturbations prevent any satisfactory fit to the ν₁₃ band.     

The Vibrational Ground State of CHD3

Within the scope of a general tensorial study of the 1000 and 2000 cm⁻¹ polyads of CHD₃, we have revisited the ground state of this molecule. Infrared ground state combination differences (GSCD) were calculated from 1746 transitions assigned in the ν₃/ν₅/ν₆ triad of CHD₃. A set of 10 ground state parameters has been fitted to 613 GSCD providing an agreement of 0.00014 cm⁻¹ between observed and calculated transitions. This corresponds to an improvement of about one order of magnitude with respect to the previous study, reflecting the quality of the experimental spectrum as well as a strict selection of the data used to fit the parameters.     

High-Resolution Infrared Spectra of the ν2, ν3, ν4, and 2ν3 Bands of SO3

New measurements are reported for the infrared spectrum of sulfur trioxide, ³²S¹⁶O₃, with resolutions ranging from 0.0015 cm⁻¹ to 0.0025 cm⁻¹. Rovibrational constants have been measured for the fundamentals ν₂, ν₃, and ν₄ and the overtone band 2ν₃. Comparisons are made with the earlier high-resolution measurements on SO₃, and the high correlation among some of the constants related to the Coriolis coupling of the ν₂ and ν₄ levels is discussed in order to understand the areas of disagreement with the earlier work. Splittings of some of the levels are observed and the splitting constant for K=3 of the ground state is determined for the first time. Other observed splittings include the K=1 levels of 2ν₃ (l=2), the K=2 levels of ν₃ and ν₄, and the K=3 levels of ν₂. The analysis shows that there are level crossings between the l=0 and l=2 states of 2ν₃ that allow one to determine the separation of the subband centers for these two states even though access to the l=0 state from the ground state is electric-dipole forbidden. This is a generalized phenomenon that should be found for many other molecules with the same symmetry. The l-type resonance constant, q₃, that causes the splitting of the l₃=±1, k=±1 levels of ν₃ also couples the l₃=0 and 2 states of 2ν₃.     

Analysis of high resolution fourier transform and diode laser spectra of the ν9 band of ethane

Fourier transform measurements with an apodized apparatus function up to 0.002 cm⁻¹ are reported for the ν₉ band (ρ_u) of ethane in the 12-μm region, together with an integrated band strength obtained from intensity measurements on selected Q-branch lines recorded using a diode laser spectrometer. Since the ν₉ band falls in an atmospheric window, these data may be useful in studies of the ethane concentration in the atmosphere of Jupiter and other outer planets. Torsional splittings in the ν₉ level caused by a higher-order Coriolis interaction with the close lying 3ν₄ state (a_1u) have been analyzed in a global least squares fit of 2206 Fourier transform lines and 58 diode splittings to a molecular Hamiltonian containing 20 parameters, with a standard deviation of 0.35 × 10⁻³ cm⁻¹. Rotational levels of one component of the torsionally split 3ν₄ state cross interacting rotational levels of the ν₉ state for K = 17, and the spectrum is followed to K = 19 on the ^pP subband side to permit inclusion of ν₉ levels beyond this crossing. No transitions to 3ν₄ levels were observed. The theoretical treatment presented here makes use of standard symmetric top formalism and of the G₃₆^† double-group formalism for ethane.     

Analysis of the ν1 + ν2 + ν3 band of O3

The high resolution spectrum of the ν₁ + ν₂ + ν₃ band of O₃ in the 2800-cm⁻¹ region has been analyzed using Watson's Hamiltonian. The resulting Hamiltonian constants and previously published line intensities have been used to generate a listing of line assignments, positions, absolute intensities, and ground state energies. These should be useful for atmospheric studies.     

A combined ab initio, Fourier transform microwave and Fourier transform infrared spectroscopic investigation of β-propiolactone: The ν8 and ν12 bands

The pure rotational spectrum of β-propiolactone (c-C₂H₄COO) has been recorded between 7 and 21 GHz using a pulsed jet Fourier transform microwave spectrometer. The resulting ground state spectroscopic constants guided the analysis of the rotationally-resolved infrared spectra of two bands that were collected using the far infrared beamline at the Canadian Light Source synchrotron. The observed modes correspond to motions best described as ring deformation (ν₁₂) at 747.2 cm⁻¹ and CO ring stretching (ν₈) at 1095.4 cm⁻¹. A global fit of 4430 a- and b-type transitions from the microwave spectrum and the two infrared bands provided an accurate set of ground state and excited state spectroscopic parameters. To complement the experimental results, the harmonic and anharmonic vibrational frequencies of all 21 infrared active modes of β-propiolactone have been calculated using the DFT B3LYP method (6-311+G(d,p), 6-311++G(2d,3p) basis sets).     

CO2: Global Treatment of Vibrational–Rotational Spectra and First Observation of the 2ν1 + 5ν3 and ν1 + 2ν2 + 5ν3 Absorption Bands

The effective operator approach is applied to the calculation of both line positions and line intensities of the ¹³C¹⁶O₂ molecule. About 11 000 observed line positions of ¹³C¹⁶O₂ selected from the literature have been used to derive 84 parameters of a reduced effective Hamiltonian globally describing all known vibrational–rotational energy levels in the ground electronic state. The standard deviation of the fit is 0.0015 cm⁻¹. The eigenfunctions of this effective Hamiltonian have then been used in fittings of parameters of an effective dipole-moment operator to more than 600 observed line intensities of the cold and hot bands covering the ν₂ and 3ν₂ regions. The standard deviations of the fits are 3.2 and 12.0% for these regions, respectively. The quality of the fittings and the extrapolation properties of the fitted parameters are discussed. A comparison of calculated line parameters with those provided by the HITRAN database is given. Finally, the first observations of the 2ν₁ + 5ν₃ and ν₁ + 2ν₂ + 5ν₃ absorption bands by means of photoacoustic spectroscopy (PAS) is presented. The deviations of predicted line positions from observed ones is found to be less than 0.1 cm⁻¹, and most of them lie within the experimental accuracy (0.007 cm⁻¹) once the observed line positions are included in the global fit.     

Measurements of line intensities and determination of transition moment parameters from experimental data for the ν1 and ν3 bands of D2S

First measurements of line intensities for ν₁ and ν₃ bands of D₂³²S are reported. About 300 intensities of D₂³²S vibration–rotation lines were obtained from experimental high-resolution spectra recorded in the 1810–2051 cm⁻¹ region with the Fourier Transform Spectrometer built in Reims. Empirical values of transition moment parameters for ν₁ and ν₃ bands of D₂³²S were determined for the first time using a least-square fit to the observed intensities. Experimental D₂³²S intensities were compared with recent global variational predictions [Vl.G. Tyuterev, L. Régalia-Jarlot, D.W. Schwenke, S.A. Tashkun, Y.G. Borkov, C. R. Phys. 5 (2004) 189–199] computed from isotopically invariant potential and dipole moment functions of the hydrogen sulphide molecule. Average discrepancy between these calculations and our observed data was 0.03 cm⁻¹ for line positions of this spectral range. The discrepancy between these calculations and our measurements for the sum of line intensities was 5.5% and 3.5% for the ν₁ and ν₃ bands, correspondingly.     

Rotational fine structure of the perpendicular band, ν7, of ethane-1,1,1-d3

The gas-phase infrared spectrum of CH₃CD₃ in the region of the perpendicular C---H stretching band, ν₇, near 3000 cm⁻¹ has been studied under a spectral resolution of 0.025 cm⁻¹, increased to 0.015 cm⁻¹ by deconvolution. An assignment of lines in the subbands KΔK = +15 to −3 is proposed, and their upper-state constants are reported. The interpretation of the effective rotational constants of the individual subbands is complicated by a strong perturbation.     

The ν1 and ν3 Bands of the OOO Isotopomer of Ozone

Using 0.002 cm⁻¹ resolution Fourier transform absorption spectra of an ¹⁷O-enriched ozone sample, an extensive analysis of the ν₃ band together with a partial identification of the ν₁ band of the ¹⁷O¹⁶O¹⁷O isotopomer of ozone has been performed for the first time. As for other C_2v-type ozone isotopomers [J.-M. Flaud and R. Bacis, Spectrochim. Acta, Part A 54, 3–16 (1998)], the (001) rotational levels are involved in a Coriolis-type resonance with the levels of the (100) vibrational state. The experimental rotational levels of the (001) and (100) vibrational states have been satisfactorily reproduced using a Hamiltonian matrix which takes into account the observed rovibrational resonances. In this way precise vibrational energies and rotational and coupling constants were deduced and the following band centers ν₀(ν₃) = 1030.0946 cm⁻¹ and ν₀(ν₁) = 1086.7490 cm⁻¹ were obtained for the ν₃ and ν₁ bands, respectively.     

Analysis of the ν3 band of NO2

The rotational structure of the ν₃ fundamental of ¹⁴N¹⁶O₂ has been recorded by employing a vacuum grating infrared spectrograph. The analysis has led to the assignment of over 500 R- and P-branch transitions in the spectral region 1562–1650 cm⁻¹. Molecular constants for the upper state, 001, have been presented. No Q-branch transitions were used in the evaluation of these constants. The presently obtained and the band center ν₀ = 1616.846 cm⁻¹ differ significantly from previous determinations. Spin splitting was observed but no information was extracted about upper state spin splitting parameters.     

The ν2, ν5 Raman band system of CH3F

The anisotropic and isotropic components of the ν₂, ν₅ rotation-vibrational Raman bands of ¹³CH₃F were obtained separately. The two upper states are coupled by a strong second-order Coriolis resonance. The anisotropic spectrum was analyzed by means of a program system due to R. Escribano. A contour simulation and a least-squares fit of 233 assigned transitions yielded values for ν₅, ΔA₅, ΔA₂, and Aζ_{5a, 5b^(z)}. The ¹³C shifts of ν₂ and ν₅ were obtained from the isotropic spectrum.