Line mixing effects in the ν2 + ν3 band of methane

This study provides the first direct experimental measurements of the off-diagonal relaxation matrix element coefficients for line mixing in air-broadened methane spectra for any vibrational band and the first off diagonal relaxation matrix elements associated with line mixing for pure methane in the ν₂ + ν₃ band of ¹²CH₄. The speed-dependent Voigt profile with line mixing is used with a multispectrum nonlinear least squares curve fitting technique to retrieve the various line parameters from 11 self-broadened and 10 air-broadened spectra simultaneously. The room temperature spectra analyzed in this work are recorded at 0.011 cm⁻¹ resolution with the McMath-Pierce Fourier transform spectrometer located at the National Solar Observatory, Kitt Peak, Arizona. The off-diagonal relaxation matrix element coefficients of ν₂ + ν₃ transitions between 4410 and 4629 cm⁻¹ are reported for eighteen pairs with upper state J values between 2 and 11. The observed line mixing coefficients for self broadening vary from 0.0019 to 0.0390 cm⁻¹ atm⁻¹ at 296 K. The measured line mixing coefficients for air broadening vary from 0.0005 to 0.0205 cm⁻¹ atm⁻¹ at 296 K.     

Measurements and theoretical calculations of self-broadening and self-shift coefficients in the ν2 band of CH3D

In this paper, we report measured Lorentz self-broadening and self-induced pressure-shift coefficients of ¹²CH₃D in the ν₂ fundamental band (ν₀ ≈ 2200 cm⁻¹). The multispectrum fitting technique allowed us to analyze simultaneously seven self-broadened absorption spectra. All spectra were recorded at the McMath-Pierce Fourier transform spectrometer of the National Solar Observatory (NSO) on Kitt Peak, AZ with an unapodized resolution of 0.0056 cm⁻¹. Low-pressure (0.98-2.95 Torr) as well as high-pressure (17.5-303 Torr) spectra of ¹²C-enriched CH₃D were recorded at room temperature to determine the pressure-broadening coefficients of 408 ν₂ transitions with quantum numbers as high as J″ = 21 and K = 18, where K″ = K′ ≡ K (for a parallel band). The measured self-broadening coefficients range from 0.0349 to 0.0896 cm⁻¹ atm⁻¹ at 296 K. All the measured pressure-shifts are negative. The reported pressure-induced self-shift coefficients vary from about −0.004 to −0.008 cm⁻¹ atm⁻¹. We have examined the dependence of the measured broadening and shift parameters on the J″, and K quantum numbers and also developed empirical expressions to describe the broadening coefficients in terms of m (m = −J″, J″, and J″ + 1 in the ^QP-, ^QQ-, and ^QR-branch, respectively) and K. On average, the empirical expressions reproduce the measured broadening coefficients to within 3.6%. A semiclassical theory based upon the Robert-Bonamy formalism of interacting linear molecules has been used to calculate these self-broadening and self-induced pressure-shift coefficients. In addition to the electrostatic interactions involving the octopole and hexadecapole moments of CH₃D, the intermolecular potential includes also an atom-atom Lennard-Jones model. For low K (K ? 3) with |m| ? 8 the theoretical results of the broadening coefficients are in overall good agreement (3.0%) with the experimental data. For transitions with K approaching |m|, they are generally significantly underestimated (8.8%). The theoretical self-induced pressure shifts, whose vibrational contribution is derived from results in the ^QQ-branch, are generally smaller in magnitude than the experimental data in the ^QP-, and ^QR-branches (15.2%).     

The absorption spectrum of phosphine (PH3) between 2.8 and 3.7 μm: Line positions, intensities, and assignments

Over 8000 line positions and intensities of phosphine (PH₃) at 3 μm have been measured at 0.0115 cm⁻¹ resolution with the McMath-Pierce Fourier Transform spectrometer at Kitt Peak. The observed line intensities ranged from 4.13 × 10⁻⁶ to 4.69 × 10⁻² cm⁻² atm⁻¹ at 296 K, for line positions between 2724.477 and 3601.652 cm⁻¹. This region spans eight interacting vibrational states: 3ν₂ (2940.8 cm⁻¹), 2ν₂ + ν₄ (3085.6 cm⁻¹), ν₂ + 2ν₄ (3214.9 cm⁻¹), ν₁ + ν₂ (3307.6 cm⁻¹), ν₂ + ν₃ (3310.5 cm⁻¹), 3ν₄ (∼3345 cm⁻¹), ν₁ + ν₄ (3426.9 cm⁻¹), and ν₃ + ν₄ (3432.9 cm⁻¹). Assignments have been determined for all the bands except 3ν₄ (a weak band in a highly congested area) for a total of 4232 transitions. The total integrated intensity for this region is 5.70 cm⁻² atm⁻¹ near 296 K, and assigned lines account for 79% of the observed absorption. The two strongest bands in the region are ν₁ + ν₄ and ν₃ + ν₄ with band strengths at 296 K of 1.61 and 2.01 cm⁻² atm⁻¹, respectively. An empirical database of PH₃ line parameters (positions, intensities, and assignments) is now available. Lower state energies (corresponding to assignments from this study) and line widths from the literature are included; default values are used for unassigned features.     

Measurements and theoretical calculations of N2-broadening and N2-shift coefficients in the ν2 band of CH3D

In this paper, we report measured Lorentz N₂-broadening and N₂-induced pressure-shift coefficients of CH₃D in the ν₂ fundamental band using a multispectrum fitting technique. These measurements were made by analyzing 11 laboratory absorption spectra recorded at 0.0056 cm⁻¹ resolution using the McMath-Pierce Fourier transform spectrometer located at the National Solar Observatory on Kitt Peak, Arizona. The spectra were obtained using two absorption cells with path lengths of 10.2 and 25 cm. The total sample pressures ranged from 0.98 to 402.25 Torr with CH₃D volume mixing ratios of 0.01 in nitrogen. We have been able to determine the N₂ pressure-broadening coefficients of 368 ν₂ transitions with quantum numbers as high as J″ = 20 and K = 16, where K″ = K′ ≡ K (for a parallel band). The measured N₂-broadening coefficients range from 0.0248 to 0.0742 cm⁻¹ atm⁻¹ at 296 K. All the measured pressure-shifts are negative. The reported N₂-induced pressure-shift coefficients vary from about −0.0003 to −0.0094 cm⁻¹ atm⁻¹. We have examined the dependence of the measured broadening and shift parameters on the J″, and K quantum numbers and also developed empirical expressions to describe the broadening coefficients in terms of m (m = −J″, J″, and J″ + 1 in the ^QP-, ^QQ-, and ^QR-branch, respectively) and K. On average, the empirical expressions reproduce the measured broadening coefficients to within 4.7%. The N₂-broadening and pressure-shift coefficients were calculated on the basis of a semiclassical model of interacting linear molecules performed by considering in addition to the electrostatic contributions the atom-atom Lennard-Jones potential. The theoretical results of the broadening coefficients are in good overall agreement with the experimental data (8.7%). The N₂-pressure shifts whose vibrational contribution is derived from parameters fitted in the ^QQ-branch of self-induced shifts of CH₃D, are also in reasonable agreement with the scattered experimental data (20% in most cases).     

Room-temperature broadening and pressure-shift coefficients in the ν2 band of CH3D-O2: Measurements and semi-classical calculations

We report measured Lorentz O₂-broadening and O₂-induced pressure-shift coefficients of CH₃D in the ν₂ fundamental band. Using a multispectrum fitting technique we have analyzed 11 laboratory absorption spectra recorded at 0.011 cm⁻¹ resolution using the McMath-Pierce Fourier transform spectrometer, Kitt Peak, Arizona. Two absorption cells with path lengths of 10.2 and 25 cm were used to record the spectra. The total sample pressures ranged from 0.98 to 339.85 Torr with CH₃D volume mixing ratios of 0.012 in oxygen. We report measurements for O₂ pressure-broadening coefficients of 320 ν₂ transitions with quantum numbers as high as J″ = 17 and K = 14, where K″ = K′ ≡ K (for a parallel band). The measured O₂-broadening coefficients range from 0.0153 to 0.0645 cm⁻¹ atm⁻¹ at 296 K. All the measured pressure-shifts are negative. The reported O₂-induced pressure-shift coefficients vary from about −0.0017 to −0.0068 cm⁻¹ atm⁻¹. We have examined the dependence of the measured broadening and shift parameters on the J″, and K quantum numbers and also developed empirical expressions to describe the broadening coefficients in terms of m (m = −J″, J″, and J″ + 1 in the ^QP-, ^QQ-, and ^QR-branch, respectively) and K. On average, the empirical expressions reproduce the measured broadening coefficients to within 4.4%. The O₂-broadening and pressure shift coefficients were calculated on the basis of a semiclassical model of interacting linear molecules performed by considering in addition to the electrostatic contributions the atom-atom Lennard-Jones potential. The theoretical results of the broadening coefficients are generally larger than the experimental data. Using for the trajectory model an isotropic Lennard-Jones potential derived from molecular parameters instead of the spherical average of the atom-atom model, a better agreement is obtained with these data, especially for |m| ? 12 values (11.3% for the first calculation and 8.1% for the second calculation). The O₂-pressure shifts whose vibrational contribution are either derived from parameters fitted in the ^QQ-branch of self-induced shifts of CH₃D or those obtained from pressure shifts induced by Xe in the ν₃ band of CH₃D are in reasonable agreement with the scattered experimental data (17.0% for the first calculation and 18.7% for the second calculation).     

Multispectrum analysis of CH4 from 4100 to 4635 cm: II. Air-broadening coefficients (widths and shifts)

Room temperature Lorentz air-broadened halfwidth and pressure-induced air-shift coefficients were measured for 1011 transitions in the octad region of methane between 4100 and 4635 cm⁻¹. These measurements were made by analyzing 10 laboratory absorption spectra recorded at 0.011 cm⁻¹ resolution using the McMath-Pierce Fourier transform spectrometer located at the National Solar Observatory on Kitt Peak, Arizona. The spectra were obtained using two absorption cells with path lengths of 2.05 and 150 cm. The total sample pressures ranged from 99 to 400 torr with CH₄ volume mixing ratios of 0.01 in dry air. The spectral line parameters were retrieved using a multispectrum nonlinear least squares technique. Transitions belonging to five bands of the octad polyad were observed, namely ν₂ + 2ν₄, ν₁ + ν₄, ν₃ + ν₄, 2ν₂ + ν₄, and ν₂ + ν₃. The numbers of measurements by bands are: 33 for ν₂ + 2ν₄, 180 for ν₁ + ν₄, 635 for ν₃ + ν₄, 33 for 2ν₂ + ν₄, and 130 for ν₂ + ν₃. Transitions with rotational quantum number J up to 16 are included in the analysis. The measured width and shift coefficients vary according to the tetrahedral symmetry species and the rotational quantum numbers of the transitions. The retrieved parameters from this study are compared with prior results, in part to estimate absolute accuracy and determine the extent of vibrational dependence of widths and shifts.     

Multispectrum analysis of the ν4 band of CH3CN: Positions, intensities, self- and N2-broadening, and pressure-induced shifts

A multispectrum nonlinear least-squares fitting technique was applied to measure accurate zero-pressure line center positions, Lorentz self- and nitrogen (N₂)-broadened half-width coefficients, and self- and N₂-pressure-induced shift coefficients for over 700 transitions in the parallel ν₄ band of CH₃CN near 920 cm⁻¹. Fifteen high-resolution (0.0016 cm⁻¹) laboratory absorption spectra of pure and N₂-broadened CH₃CN recorded at room temperature using the Bruker IFS 125HR Fourier transform spectrometer located at the Pacific Northwest National Laboratory (PNNL) in Richland, Washington, USA, were analyzed simultaneously assuming standard Voigt line shapes. Short spectral intervals containing manifolds of transitions from the same value of J were fitted together. In all, high-precision line parameters were obtained for P(44)-P(3) and R(0)-R(46) manifolds. As part of the analysis, quantum assignments were extended, and the total internal partition function sum was calculated for four isotopologs: ¹²CH₃¹²CN, ¹³CH₃¹²CN, ¹²CH₃¹³CN, and ¹³CH₃¹³CN. Measurements of N₂ broadening, self-broadening, N₂-shift, and self-shift coefficients for transitions with J up to 48 and K up to 12 were measured for the first time in the mid-infrared. Self-broadened half-width coefficients were found to be very large (up to ∼2 cm⁻¹ atm⁻¹ at 296 K). Ratios of self-broadened half-width coefficients to N₂-broadened half-width coefficients show a compact distribution with rotational quantum number in both the P and R branches that range from ∼4.5 to 14 with maxima near ∣m∣=24, where m=−J″, J″, and J″+1 for P, Q, and R lines, respectively. Pressure-induced shifts for N₂ are small (few exceed ±0.006 cm⁻¹ atm⁻¹ at 294 K) and are both positive and negative. In contrast, self-shift coefficients are large (maxima of about ±0.08 cm⁻¹ atm⁻¹ at 294 K) and are both positive and negative as a function of rotational quantum numbers. The present measured half-widths and pressure shifts in ν₄ were compared with corresponding measurements of rotational transitions.     

High-resolution infrared spectra of OOO ozone isotopomer in the range 900-5000 cm: line positions

Continuing the systematic study of ozone high-resolution infrared spectra, we present in this paper the measurements and analyses of line positions for the ¹⁸O¹⁶O¹⁸O isotopomer. In the range 900-5000 cm⁻¹, corresponding to the observed spectra, 15 bands are analysed: ν₁, ν₃, ν₂+ν₃, ν₁+ν₂, 2ν₃, ν₁+ν₃, 2ν₁, ν₂+2ν₃, ν₁+ν₂+ν₃, 3ν₃, 2ν₁+ν₃, ν₂+3ν₃, ν₁+3ν₃, ν₁+ν₂+3ν₃, and 5ν₃. As in the case of ¹⁶O₃, ¹⁸O₃, and ¹⁶O¹⁸O¹⁶O, the analysis of these bands is performed using effective rovibrational Hamiltonians for nine polyads of interacting upper vibrational states. To correctly reproduce all observed transitions, we have to account for resonance perturbations due to 13 “Dark” states: (0 3 0), (0 4 0), (2 1 0), (0 3 1), (1 0 2), (0 4 1), (1 1 2), (3 1 0), (0 3 2), (0 0 4), (3 2 0), (0 1 4), and (0 4 2). We present the range of observed transitions, the results for spectroscopic parameters (vibrational energy levels, rotational and centrifugal distortion constants, and resonance coupling parameters), as well as the statistics for rovibrational energy levels, calculations and measurements. A comparison of observed band centres with those predicted from an isotopically invariant potential function is discussed. The RMS deviation between predicted and directly observed band centres is ≈0.03 cm⁻¹ up to 3000 and ≈0.25 cm⁻¹ for all 16 bands up to 5000 cm⁻¹.     

Pressure broadening coefficients of ν5 fundamental band lines of CH3I at 7 μm measured by diode laser absorption spectroscopy

We have measured the room temperature pressure broadening coefficients, γ, of over 100 lines in five Q-branches of the ν₅ perpendicular band of methyl iodide (¹²CH₃I) using tuneable diode laser absorption spectroscopy. The profiles of individual lines in the ^PQ₂, ^PQ₄, ^PQ₅, ^PQ₆ and ^RQ₃ branches were recorded in a 1 m long White cell and at nitrogen or oxygen pressures up to 15 Torr. The lines were fitted to the Voigt profile to obtain the collision broadened line widths. Within individual Q-branches the broadening coefficients decreased monotonically with increasing J and for nitrogen broadening varied between 0.19 cm⁻¹ atm⁻¹ at low J and 0.12 cm⁻¹ atm⁻¹ at high J. The corresponding oxygen broadening coefficients were approximately 20% smaller. Self broadening coefficients were also measured for several of the Q-branches and found to be up to ∼4 times higher than the corresponding nitrogen broadening values.     

CW-Cavity Ring Down Spectroscopy of the ozone molecule in the 5980-6220 cm region

The absorption spectrum of ozone, ¹⁶O₃, has been recorded in the 5980-6220 cm⁻¹ region by high sensitivity CW-Cavity Ring Down Spectroscopy (α_min ∼ 3 × 10⁻¹⁰ cm⁻¹). This study extends a first investigation with the same experimental set-up limited to the 6030-6090 cm⁻¹ spectral region [M.-R. De Backer-Barilly, A. Barbe, Vl.G. Tyuterev, D. Romanini, B. Moeskops, A. Campargue, J. Mol. Struct. 780-781 (2006) 225-233] where the analysis of two A-type bands was reported, using FTS spectra for complementary information. The spectral extension of the recordings allows not only to enlarge considerably the observed transitions of these two bands, but more importantly, to assign four new bands: the 3ν₂ + 4ν₃,5ν₁ + ν₂ and ν₁ + 2ν₂ + 4ν₃ B-type bands which were considered as dark in our previous report and the 3ν₁ + 3ν₂ + ν₃ A-type band. The high mixing of the observed states approaching the dissociation limit, leads to the breakdown of the polyad structure and ambiguities in the vibrational labelling which are discussed. Finally, 1789 transitions were assigned, and a suitable Hamiltonian model allows reproducing correctly the observations for five of the six observed bands. The list of 1004 experimentally determined energy levels is provided. The determined effective Hamiltonian and transition moment operators were used to generate a list of 5338 transitions given as Supplementary Material. It is interesting to note that the d₅ parameter of the effective transition moment is of great importance to account for the observed intensities of the B-type bands.     

Analysis of the high-resolution infrared spectrum of cyclopropane

The high-resolution infrared spectrum of cyclopropane (C₃H₆) has been measured from 100 cm⁻¹ to 2200 cm⁻¹. In that region we have identified 24 absorption bands attributed to six fundamental bands, five combination bands, three hot bands and 10 difference bands. Long pathlength spectra, up to 32 m, facilitated the identification and analysis of many previously unstudied infrared inactive, and Raman and infrared inactive vibrational states, including direct access to two forbidden fundamental states, ν₄ and ν₁₄. An improved set of constants for the ground vibrational state as well as for the fundamental vibrations ν₇, ν₉, ν₁₀, ν₁₁ are also reported. The spectral resolution of the measurements varied from 0.002 cm⁻¹ to 0.004 cm⁻¹.     

Preliminary analysis of CH3D from 3250 to 3700 cm

The infrared spectrum of CH₃D from 3250 to 3700 cm⁻¹ was studied for the first time to assign transitions involving the ν₂ + ν₃, ν₂ + ν₅, ν₂ + ν₆, ν₃ + 2ν₆ and 3ν₆ vibrational states. Line positions and intensities were measured at 0.011 cm⁻¹ resolution using Fourier transform spectra recorded at Kitt Peak with isotopically enriched samples. Some 2852 line positions (involving over 900 upper state levels) and 874 line intensities were reproduced with RMS values of 0.0009 cm⁻¹ and 4.6%, respectively. The strongest bands were found to be ν₂ + ν₃ at 3499.7 cm⁻¹ and ν₂ + ν₆ at 3342.5 cm⁻¹ with integrated strengths, respectively, of 8.17 × 10⁻²⁰ and 2.44 × 10⁻²⁰ (cm⁻¹/molecule · cm⁻²) at 296 K (for 100% CH₃D). The effective Hamiltonian was expressed in terms of irreducible tensor operators and adapted to symmetric top molecules. Its present configuration in the MIRS package permitted simultaneous consideration of the four lowest polyads of CH₃D: the Ground State (G.S.), the Triad from 6.3 to 9.5 μm, the Nonad from 3.1 to 4.8 μm and now the Enneadecad (19 bands) from 2.2 to 3.1 μm. The CH₃D line parameters for this interval were calculated to create a new database for the 3 μm region.     

CRDS spectroscopy of O3. Part 2: Analysis of six interacting bands between 5930 and 6080 cm

The absorption spectrum of ¹⁸O₃ has been recorded in the 5930-6080 cm⁻¹ region using CW-Cavity Ring Down Spectroscopy. 1888 transitions belonging to five bands have been assigned. Three of them are A-type bands: 2ν₂ + 5ν₃, ν₁ + ν₂ + 5ν₃ and 5ν₁ + ν₃, and two bands are of B-type: 2ν₁ + ν₂ + 4ν₃ and 4ν₁ + 3ν₂. Despite a complex spectral pattern perturbed by many rovibrational resonances, it has been possible to find a suitable effective Hamiltonian model reproducing all the transition wavenumbers (corresponding to 1016 energy levels) with an rms deviation of 9.5 × 10⁻³ cm⁻¹. A set of 721 line intensities was determined and fitted to derive the effective transition moment parameters. This set of parameters and the experimental energy levels were used to generate a complete line list of 2795 transitions allowing to generate synthetic spectrum in good agreement with the experimental spectrum.     

The vibration-rotation spectrum of C2HD: new overtone bands and global vibrational analysis

Two new bands, 2ν₁+ν₂+ν₃+2ν₅ and 5ν₃ with origin at 12220.692 and 12496.158 cm⁻¹, respectively, were identified on new FT-ICLAS spectra of ¹²C₂HD and rotationally analyzed. The rotational analysis of two known bands, with origin at 12038.538 and 12234.872 cm⁻¹ was extended. Another band, 2ν₁+2ν₅ with origin at 7843.6622 cm⁻¹, was identified for the first time and rotationally analyzed, from a high pressure conventional FT spectrum. Some 115 known vibrational state energies in the molecule, extending up to the visible range, were used to produce updated vibrational constants. Both a straightforward Dunham model and a global model accounting for a single anharmonic resonance, K_1/255, were used. The results are discussed.     

Observation of hot bands in the infrared spectrum of H2CO

Two hot bands in the infrared spectrum of formaldehyde (H₂CO) have been identified by means of tunable infrared laser spectroscopy using a jet-cooled sample. One band falls in the region 2760-2800 cm⁻¹; it follows a-type selection rules and it has been assigned as the ν₁ + ν₄ − ν₄ hot band. The other band falls in the region 2800-2860 cm⁻¹; it follows b-type selection rules and it has been assigned as the ν₅ + ν₄ − ν₄ hot band. The observations are restricted to low J and K_a levels. It has consequently been possible to ignore the effects of the extensive Coriolis couplings involving these levels in the analysis of the spectra and to model the rotational structure as that of a simple asymmetric top. Least-squares fits of the data have provided values for the band origins: 2774.2706(11) cm⁻¹ for the ν₁ + ν₄ − ν₄ and 2829.2621(8) cm⁻¹ for the ν₅ + ν₄ − ν₄ band. Term values for the upper vibrational levels involved in the transitions have been determined by use of the previously reported term values for the v₄ = 1 level.     

High resolution study of the six lowest doubly excited vibrational states of PH2D

The five lowest doubly excited deformational vibrational bands ν₄ + ν₆, 2ν₆, ν₃ + ν₄, ν₃ + ν₆, and 2ν₃ of PH₂D have been recorded for the first time using a Bruker 120 HR interferometer with a resolution 0.0033 cm⁻¹ and analysed. Some transitions belonging to a very weak band 2ν₄ have been also assigned. From the fit 24 and 86, respectively, diagonal and resonance interaction parameters were obtained which reproduce 1089 upper energy levels obtained from more than 4600 assigned transitions with the rms deviation of 0.00059 cm⁻¹.     

Joint ro-vibrational analysis of the HDS high resolution infrared data

High resolution Fourier transform spectra of the HDS molecule were recorded and analyzed for the first time in the region of the bands ν₁ + 2ν₂ (3938.6 cm⁻¹), ν₁ + ν₃ (4522.6 cm⁻¹), 2ν₂ + ν₃ (4638.8 cm⁻¹), 2ν₁ + ν₂ (4767.7 cm⁻¹), ν₁ + ν₂ + ν₃ (5525.2 cm⁻¹), 3ν₁ (5560.6 cm⁻¹), ν₁ + 2ν₃ (7047.2 cm⁻¹), and 2ν₂ + 2ν₃ (7123.9 cm⁻¹). The ro-vibrational energies of the upper vibrational states of these bands together with the ro-vibrational energies of 12 other bands already studied at high resolution were used as inputs in a Global Fit analysis firstly described in [O.N. Ulenikov, G.A. Onopenko, H. Lin, J.-H. Zhang, Z.-Y. Zhou, Q.-S. Zhu, R.N. Tolchenov, J. Mol. Spectrosc. 189 (1998) 29-39]. In this case, the resonance interactions between the states (v₁v₂v₃) and (v₁ ± 2 v₂ ? 1 v₃ ? 1) were taken into account. The resulting set of 143 parameters reproduces all the experimental data (2984 vibration-rotation energies of 20 vibrational states which correspond to about 9700 ro-vibrational transitions with J^max = 23) with accuracies comparable with the experimental uncertainties.     

Transferring the high accuracy of the 10 μm CO2 laser bands to far infrared region with internal calibration of CS2

The main aim of the work is to transfer the high accuracy of the CO₂ laser bands around 10 μm to far infrared regions around 400 and 250 cm⁻¹ for secondary standards. The bands ν₁ + ν₂ and 3ν₂ of CS₂ were measured on the Bruker IFS 120 HR Fourier spectrometer in Oulu with special care and calibrated against CO₂. In the second stage the ν₂ region around 400 cm⁻¹ was measured at a resolution of 0.001 cm⁻¹. This spectrum was calibrated against 3ν₂ internally with the CS₂ band system using ladders formed with rotational lines in the bands ν₂, 2ν₂ − ν₂ and 3ν₂ − 2ν₂. Further, the difference band ν₁ − ν₂ at 263 cm⁻¹ together with accompanying hot bands was measured on a similar spectrometer in Lund, Sweden, but with a synchrotron radiation source. Using corresponding chains of lines as above this region was calibrated with ν₁ + ν₂. In this way, problems with conventional calibration could be avoided. Without the effect of the pressure shifts the absolute accuracy of 2.0 × 10⁻⁶ and 8.4 × 10⁻⁶ cm⁻¹ has been achieved at 400 and 250 cm⁻¹, respectively. Simultaneously the same calibration accuracy is also transferred to residual water lines around the CS₂ far infrared bands and the best H₂O lines will be given with literature comparisons. In addition to the calibration new results from the observed hot bands of CS₂ in the region of the bands ν₁ + ν₂ and 3ν₂ will be given.     

CW-cavity ring down spectroscopy of the ozone molecule in the 6220-6400 cm region

The absorption spectrum of ozone,¹⁶O₃, has been recorded in the 6220-6400 cm⁻¹ region by high sensitivity CW-cavity ring down spectroscopy (α_min ∼ 3 × 10⁻¹⁰ cm⁻¹). 1836 rovibrational transitions have been assigned to the 2ν₂ + 5ν₃, 5ν₁ + ν₃ and 2ν₁ +  2ν₂ + 3ν₃ A-type bands centred at 6305, 6355 and 6387 cm⁻¹, respectively. In addition, 99 lines of the very weak ν₁ + 2ν₂ +  4ν₃ and 4ν₁ + 3ν₂ B-type bands are identified. The modeling of the observed spectrum in the effective Hamiltonian approach was particularly laborious and complex as several rovibrational interactions of both Coriolis and anaharmonic type were found to be of importance, in particular for the (124) vibrational state. Nevertheless, it has finally been possible to fit the 990 experimentally determined energy levels with an rms deviation of 8.29 × 10⁻³ cm⁻¹ and to derive the transition moment parameters allowing a satisfactory reproduction of the observed intensities. As the differences in positions between the final calculations and observations are still larger than the experimental accuracy, we provide the list of all energy levels derived from the observation, in addition to their differences with the calculated ones. These experimental energy levels, with the transition moment parameters were used to generate a line-list of 2451 transitions, reproducing the observed spectrum. This list is given as Supplementary Material.     

A multispectrum analysis of the ν2 band of HCN: Part I. Intensities, broadening, and shift coefficients

Absolute intensities, self- and air-broadening coefficients, self- and air-induced shift coefficients and their temperature dependences have been determined for lines belonging to the P- and R-branches of the ν₂ band of H¹²C¹⁴N centered near 712 cm⁻¹. Infrared spectra of HCN in the 14-μm region were obtained at high resolution (0.002-0.008 cm⁻¹) using two different Fourier transform spectrometers (FTS), the McMath-Pierce FTS at the National Solar Observatory on Kitt Peak and the Bruker IFS 120HR FTS at the Pacific Northwest National Laboratory. Spectra were recorded with 99.8% pure HCN as well as lean mixtures of HCN in air at various temperatures ranging between +26 and −60 °C. A multispectrum nonlinear least squares technique was used to fit selected intervals of 36 spectra simultaneously to obtain the line positions, intensities, broadening, and shift parameters. The measured line intensities were analyzed to determine the vibrational band intensity and the Herman-Wallis coefficients. The measured self-broadening coefficients vary between 0.2 and 1.2 cm⁻¹ atm⁻¹ at 296 K, and the air-broadening coefficients range from 0.08 to 0.14 cm⁻¹ atm⁻¹ at 296 K. The temperature dependence exponents of self-broadening range from 1.46 to −0.12 while the corresponding exponents for air broadening vary between 0.58 and 0.86. The present measurements are the first known determination of negative values for the temperature dependence exponents of HCN-broadening coefficients. We were able to support our self-broadening measurements with appropriate theoretical calculations. Our present measurements are compared, where possible, with previous measurements for this and other HCN bands, as well as the parameters that are included in the 2000 and 2004 editions of the high-resolution transmission (HITRAN) database.