High-accuracy frequency atlas of 13C2H2 in the 1.5 μm region

A pair of 1.5 μm semiconductor laser frequency standards have been developed for optical telecommunications use, stabilised to Doppler-free transitions of the ν₁ + ν₃ and ν₁ + ν₂ + ν₄ + ν₅ combination bands of ¹³C₂H₂. The Allan deviation σ/f for a laser locked to line P(10) of the former band follows a slope of 1.6 × 10⁻¹²τ^−1/2, reaching a minimum of 5.7 × 10⁻¹⁴ at τ = 4000 s. The absolute frequencies of 61 lines of the ν₁ + ν₃ band and 43 lines of the ν₁ + ν₂ + ν₄ + ν₅ band, covering the spectral region 1520 nm to 1552 nm, have been measured by use of a combined frequency chain and femtosecond comb, together with a passive optical frequency comb generator. The mean uncertainties for the line frequencies within each band are 1.4 kHz for the ν₁ + ν₃ band and 1.9 kHz for the ν₁ + ν₂ + ν₄ + ν₅ band, representing improvements on the precision of previously published data by factors of 100 and 10⁴, respectively. Improved values of the rotational constant B″ and centrifugal distortion coefficients D″, H″ and L″ of the vibrational ground state are presented.This article is published with the permission of the Controller of HMSO and the Queen’s Printer of Scotland     

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 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.     

Atmospheric neutrinos in the Soudan-2 and MACRO experiments

The results of Soudan-2 and MACRO experiments are summarized. Both experiments observe atmospheric neutrino anomalies in agreement with ν_μ → ν_τ oscillations with maximum mixing. The ν_μ → ν_s oscillations are disfavoured by the MACRO experiment at 98% C.L.     

Analysis of the Coriolis-coupled band system of ν5, ν2, and 2ν3 of methyl-d3 iodide

The Coriolis-coupled band system of ν₅, ν₂, and 2ν₃ of CD₃I was analyzed by making use of all of the experimental data now available. These data included the high-resolution infrared spectra, microwave spectra, and laser Stark spectra. The analysis gave values, more precise than before, of the spectroscopic constants for ν₅, ν₂, and 2ν₃ and the interaction constants. The determination of the rotational constant A for 2ν₃ gave a value for , with which all of the α^A constants for CD₃I have been completed. These α^A values were incorporated with the known value of A₆ to give a value for A₀.     

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.     

High-resolution infrared and theoretical study of four fundamental bands of gaseous 1,3,4-oxadiazole between 800 and 1600 cm

The Fourier transform infrared spectrum of gaseous 1,3,4-oxadiazole, C₂H₂N₂O, has been recorded in the 800–1600 cm⁻¹ wavenumber region with a resolution around 0.0030 cm⁻¹. The four fundamental bands ν₉(B₁; 852.5 cm⁻¹), ν₁₄(B₂; 1078.5 cm⁻¹), ν₄(A₁; 1092.6 cm⁻¹), and ν₂(A₁; 1534.9 cm⁻¹) are analyzed by the standard Watson model. Ground state rotational and quartic centrifugal distortion constants are obtained from a simultaneous fit of ground state combination differences from three of these bands and previous microwave transitions. Upper state spectroscopic constants are obtained for all four bands from single band fits using the Watson model. The ν₄ and ν₁₄ bands form a c-Coriolis interacting dyad, and the two bands are analyzed simultaneously by a model including first and second order Coriolis resonance using the ab initio predicted Coriolis coupling constant . An extended local resonance in ν₂ is explained as higher order b-Coriolis type resonance with ν₆ + ν₁₀, which is further perturbed globally by the ν₁₅ + ν₁₀ level. A fit of selected low-J transitions to a triad model including ν₂(A₁), ν₆ + ν₁₀(B₁), and ν₁₅ + ν₁₀(A₂) using an ab initio calculated Coriolis coupling constant is performed.The rotational constants, ground state quartic centrifugal distortion constants, anharmonic frequencies, and vibration–rotational constants (α-constants) predicted by quantum chemical calculations using a cc-pVTZ and TZ2P basis with B3LYP methodology, are compared with the present experimental data, where there is generally good agreement. A complete set of anharmonic frequencies and α-constants for all fundamental levels of the molecule is given.     

Diborane : High-resolution infrared rovibration studies of B2D6

Studies of five comparatively unperturbed infrared active bands in the spectrum of ¹⁰B₂D₆ were undertaken with a resolution of ca. 0.05 cm⁻¹. These comprise three type-A bands (ν₁₇, ν₁₈, and ν₅ + ν₁₅), one type-B band (ν₈), and one type-C band (ν₁₄). Ground-state rotational and quartic centrifugal distortion constants were determined for the first time from a total of over 400 combination differences. Sets of upper-state parameters were determined for all five bands studied, and the effects of a number of minor Coriolis interactions between fundamental vibrations are discussed.     

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.     

The vibration-rotation spectrum of C-fluorophosphaethyne FCP: Fermi resonance and harmonic force field

The vibration-rotation bands of all the fundamentals and several overtone and combination vibrations of F¹²CP have been recorded. The C-F stretching fundamental ν₃ was observed in strong Fermi resonance with the overtone 2ν₂⁰; a similar resonance was also observed between ν₁ + ν₃ and ν₁ + 2ν₁⁰. The spectral analysis gave fundamental wavenumbers: ν₁ = 1670.842 (9), ν₂ = 375.428 (6), and ν₃ = 780.10 (22) cm⁻¹. The value of the equilibrium rotational constant B_e was found to be 0.1758943 (81) cm⁻¹. The harmonic force field for this molecule was derived from the wavenumbers of the three fundamentals and the l-doubling constant.     

The hot bands of silane between 2120 and 2270 cm

The infrared spectrum of the SiH₄ molecule has been recorded between 2040 and 2320 cm⁻¹ using the high-resolution Fourier interferometer of the Laboratoire de Photophysique Moléculaire (Orsay, France). The resolution was 5.4 × 10⁻³ cm⁻¹. In this region, many lines were previously analyzed and assigned to the ν₁/ν₃ stretching dyad of ²⁸SiH₄, ²⁹SiH₄, and ³⁰SiH₄ molecules [J. Mol. Spectrosc. 143 (1990) 35]. However, several lines in the spectrum were not assigned. The results obtained in our previous study [J. Mol. Spectrosc. 197 (1999) 307] of the infrared spectrum of ²⁸SiH₄, in the bending-stretching tetrad region at 3100 cm⁻¹, enabled us to assign 204 of the observed transitions to hot bands (the ν₁ + ν₂/ν₁ + ν₄/ν₂ + ν₃/ν₃ + ν₄ bending-stretching tetrad minus the ν₂/ν₄ bending dyad). These transitions were used to refine the set of the Hamiltonian parameters of the bending-stretching tetrad. The analysis is performed using the tensorial formalism developed in Dijon for tetrahedral molecules and implemented in the STDS software (http://www.u-bourgogne.fr/LPUB/shTDS.html).     

Carbon suboxide as a semirigid bender

The semirigid bender Hamiltonian [Bunker and Landsberg, J. Mol. Spectrosc. 67, 374–385 (1977)] is used to fit the rotation-vibration energy level separations in the carbon suboxide molecule C₃O₂. We allow the CC bond lengths and CCO bond angles to change with the CCC bending angle ρ. A very good fit to the energy levels is obtained and, in particular, the B values are systematically fitted better than when the rigid bender is used. The dependence of the effective CCC bending potential function on the vibrations ν₂, ν₃, and ν₄ is determined, and we find that excitation of ν₃ or ν₄ raises the barrier to linearity whereas excitation of ν₂ lowers it. These results can be understood by considering the ρ dependence of the G-matrix elements. We determine that the barrier to CCC linearity in the zero-point vibrational state is 28 cm⁻¹ but until more data are available for the ν₁, ν₅, and ν₆ vibrations we cannot precisely determine the true barrier. However, it has been previously shown that the barrier is little affected by excitation of ν₁ or ν₅, and that it is reduced by 10–15 cm⁻¹ by excitation of ν₆. From these results we deduce that the barrier to CCC linearity in the true bending potential function is 33 cm⁻¹ with an uncertainty of about 5 cm⁻¹. Thus the equilibrium structure is bent at the central carbon atom; the equilibrium CCC angle is 157°.     

Self-broadening, self-shift and self-mixing in the ν2, 2ν2 and ν4 bands of NH3

Using Fourier-transform spectra (Bruker IFS 120 HR, resolution ≈0.004 cm⁻¹) of NH₃ in nine branches of the ν₂, 2ν₂ and ν₄ bands, self-broadening and self-shift as well as self-mixing coefficients have been determined at room temperature (T=295 K) for more than 350 rovibrational lines located in the spectral range 1000–1800 cm⁻¹. A non-linear least-squares multispectrum fitting procedure, including line mixing effects, has been used to retrieve successively the line parameters from 11 experimental spectra recorded at different pressures of pure NH₃. The accuracies of self-broadening coefficients are estimated to be better than 2% for most lines. The mean accuracies of line-mixing and line-shift data are estimated to be about 15% and 25%, respectively. The results are compared with previous measurements and with values calculated using a semiclassical model based upon the Robert–Bonamy formalism that reproduces rather well the systematic experimental J and K quantum number dependencies of the self-broadening coefficients.The results concerning line mixing demonstrate a large amount of coupling between the symmetric and asymmetric components of inversion doublets mainly in the ν₄ band. The line mixing parameters are both positive and negative. More than two thirds of the lines studied here have a positive shift coefficient. However, for most of them the shift coefficients are negative in the 2ν₂ band. They are positive for the R branch of the ν₂ band and for the ^PR and ^RP branches of the ν₄ band. For the other branches they are both positive and negative. Some components of inversion doublets illustrate a correlation between line mixing and shift phenomena demonstrated by a quadratic pressure dependence of line position.     

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.     

Diode Laser Spectroscopy of Trifluoroethylene in the 8.6-μm Region

The two mid-infrared bands of the CF₂=CHF molecule, ν₅centered at 1172.673 cm⁻¹and ν₆+ ν₉at 1155.105 cm⁻¹, were measured on a tunable diode laser spectrometer with a resolution near the Doppler limit. These vibrations ofA′ species give rise toa/bhybrid bands, even though our analysis has pointed out that the intensity of thea-type component is predominant. Most of theJandKstructure has been resolved in different subbranches, and the rovibrational analysis led to the assignment of about 1400 (J≤ 60,K_a≤ 22,K_c≤ 60) and 90 (J≤ 56,K_a≤ 5,K_c≤ 56) lines of the ν₅and ν₆+ ν₉bands, respectively. Using Watson'sA-reduction Hamiltonian in theI^rrepresentation, a set of accurate spectroscopic constants for the upper states has been derived from transitions free of major resonance effects. The rotational structure of the ν₅vibration also exhibits effects of Coriolis perturbation by a state identified as ν₇+ ν₁₁. Parameters for the perturber were determined from the interaction effects near the observed crossings, using a dyad model including first-orderb-Coriolis interaction.     

CW-Cavity Ring Down Spectroscopy of O3. Part 3: Analysis of the 6490–6900 cm region and overview comparison with the O3 main isotopologue

This paper is devoted to the third part of the analysis of the very weak absorption spectrum of the ¹⁸O₃ isotopologue of ozone recorded by CW-Cavity Ring Down Spectroscopy between 5930 and 6900 cm⁻¹. In the two first parts [A. Campargue, A. Liu, S. Kassi, D. Romanini, M.-R. De Backer-Barilly, A. Barbe, E. Starikova, S.A. Tashkun, Vl.G. Tyuterev, J. Mol. Spectrosc. (2009), doi: 10.1016/j.jms.2009.02.012 and E. Starikova, M.-R. De Backer-Barilly, A. Barbe, Vl.G. Tyuterev, A. Campargue, A.W.Liu, S. Kassi, J. Mol. Spectrosc. (2009) doi: 10.1016/j.jms.2009.03.013], the effective operators approach was used to model the spectrum in the 6200–6400 and 5930–6080 cm⁻¹ regions, respectively. The analysis of the whole investigated region is completed by the present investigation of the 6490–6900 cm⁻¹ upper range. Three sets of interacting states have been treated separately. The first one falls in the 6490–6700 cm⁻¹ region, where 1555 rovibrational transitions were assigned to three A-type bands: 3ν₂ + 5ν₃, 5ν₁ + ν₂ + ν₃ and 2ν₁ + 3ν₂ + 3ν₃ and one B-type band: ν₁ + 3ν₂ + 4ν₃. The corresponding line positions were reproduced with an rms deviation of 18.4 × 10⁻³ cm⁻¹ by using an effective Hamiltonian (EH) model involving eight vibrational states coupled by resonance interactions. In the highest spectral region – 6700–6900 cm⁻¹ – 389 and 183 transitions have been assigned to the ν₁ + 2ν₂ + 5ν₃ and 4ν₁ + 3ν₂ + ν₃ A-type bands, respectively. These very weak bands correspond to the most excited upper vibrational states observed so far in ozone. The line positions of the ν₁ + 2ν₂ + 5ν₃ band were reproduced with an rms deviation of 7.3 × 10⁻³ cm⁻¹ by using an EH involving the {(054), (026), (125)} interacting states. The coupling of the (431) upper state with the (502) dark state was needed to account for the observed line positions of the 4ν₁ + 3ν₂ + ν₃ band (rms = 5.7 × 10⁻³ cm⁻¹).The dipole transition moment parameters were determined for the different observed bands. The obtained set of parameters and the experimentally determined energy levels were used to generate a complete line list provided as Supplementary Materials.The results of the analyses of the whole 5930–6900 cm⁻¹ spectral region were gathered and used for a comparison of the band centres to their calculated values. The agreement achieved for both ¹⁸O₃ and ¹⁶O₃ (average difference on the order of 1 cm⁻¹) indicates that the used potential energy surface provides accurate predictions up to a vibrational excitation approaching 80% of the dissociation energy. The comparison of the ¹⁸O₃ and ¹⁶O₃ band intensities is also discussed, opening a field of questions concerning the variation of the dipole moments and resonance intensity borrowing by isotopic substitution.     

Coherent Raman and Infrared Studies of Sulfur Trioxide

High-resolution (0.001 cm⁻¹) coherent anti-Stokes Raman scattering (CARS) was used to observe the Q-branch structure of the IR-inactive ν₁ symmetric stretching mode of ³²S¹⁶O₃ and its various ¹⁸O isotopomers. The ν₁ spectrum of ³²S¹⁶O₃ reveals two intense Q-branches in the region 1065–1067 cm⁻¹, with surprisingly complex vibrational–rotational structure not resolved in earlier studies. Efforts to simulate this with a simple Fermi-resonance model involving ν₁ and 2ν₄ states do not reproduce the spectral detail, nor do they yield reasonable spectroscopic parameters. A more subtle combination of Fermi resonance and indirect Coriolis interactions with nearby states, 2ν₄(1=0, ±2), ν₂+ν₄(1=±1), 2ν₂(1=0), is suspected and a determination of the location of these coupled states by high-resolution infrared measurements is under way. At medium resolution (0.125 cm⁻¹), the infrared spectra reveal Q-branch features from which approximate band origins are estimated for the ν₂, ν₃, and ν₄ fundamental modes of ³²S¹⁸O₃, ³²S¹⁸O₂¹⁶O, and ³²S¹⁸O¹⁶O₂. These and literature data for ³²S¹⁶O₃ are used to calculate force constants for SO₃ and a comparison is made with similar values for SO₂ and SO. The frequencies and force constants are in excellent agreement with those obtained by Martin in a recent ab initio calculation.     

On the high resolution spectroscopy and intramolecular potential function of SO2

Two weak stretching bands, ν₁ + 3ν₃ and 3ν₁ + ν₃, of the sulfur dioxide molecule have been recorded at high resolution and analyzed for the first time with using a Fourier transform Bruker IFS-120 HR interferometer. About 1000 transitions with J^max. = 51, , and 900 transitions with J^max. = 53, have been assigned to the bands ν₁ + 3ν₃ and 3ν₁ + ν₃, respectively. Analysis of the recorded spectra was made using the model of isolated vibrational states. Parameters obtained from the fit reproduce the initial experimental ro-vibrational energies with the rms deviation of 0.0006 and 0.0012 cm⁻¹ for the bands, 3ν₁ + ν₃ and ν₁ + 3ν₃, respectively. The problem of determination of the intramolecular potential function of SO₂ is discussed.