Branch Transitions Research Articles

Mid-infrared Doppler-free saturation absorption spectroscopy of the Q branch of CH4ν3 = 1 band using a rapid-scanning continuous-wave optical parametric oscillator.

We have developed a mid-infrared Doppler-free saturation absorption spectroscopy apparatus that employs a commercial continuous-wave optical parametric oscillator (CW OPO), complemented by a home-built automation and wavelength scanning system. Here, we report a comprehensive spectral scan of the Q branch transitions of the ν3 = 1 band of methane (CH4) with an average linewidth (FWHM) of 4.5 MHz. The absolute frequency calibration was achieved using previously reported transition frequencies determined using optical frequency combs, while a Fabry-Perot etalon was used for the relative frequency calibration. We report 15 transitions with improved accuracies of 1.13 MHz (3.76 × 10-5 cm-1).

Near-infrared detection and line intensity measurements of H2S with ECDL source based off-axis integrated cavity output spectroscopy

Hydrogen sulphide (H2S) is an extremely hazardous gas which leads to poisoning at higher concentration. Here, we demonstrate the trace detection and line intensity measurement of H2S by means of efficient and indigenously developed off–axis integrated cavity output spectroscopy (OA-ICOS) technique coupled with an external cavity diode laser operating in near-infrared spectral region. Trace detection of H2S was made with OA-ICOS absorbance spectra of ro-vibrational line (51, 5 → 61, 6 & 50, 5 → 60, 6) centered at ∼ 6344 cm−1 of ν1 + ν2 + ν3 band. A ∼ 600 ppbv limit of detection was achieved for an averaging time of 350 s with Allan deviation analysis. Additionally, line intensities of several degenerate R branch transitions of ν1 + ν2 + ν3 band including 51, 5 → 61, 6 & 50, 5 → 60, 6 transition was experimentally measured with OA-ICOS. The study will be valuable in aiding the spectroscopic databases of H2S and have potential application in extracting molecular concentrations in the planet’s atmospheres.

Abstract 16382: The Surface ECG May Provide Information About Left Ventricular Systolic Function in Patients With Right Bundle Branch Block

Introduction: In patients (pts) with right bundle branch block (RBBB) and heart failure, assessment of left ventricular (LV) function is vital to management, but echocardiograms (ECHO) may not always be readily available. We studied the utility of using the Superimposed Median Format (available on digital ECG systems) in assessing LV function. This format allows visual recognition of change in dV/dT when rapid initial impulse propagation over the left bundle branch (LBB) and LV Purkinje network transitions to slower muscle-to-muscle propagation to the right ventricle (RV) in the setting of RBBB. Hypothesis: With a normal LBB and healthy LV myocardium, the transition from rapid forces to slower depolarization would occur in the 1 st half of the QRS complex ( Early Transition Group - ET) whereas in patients with abnormal LV function, this transition would occur in the 2 nd half (Late Transition Group - LT) of the QRS complex. Methods: Digital superimposed median format ECGs of 108 pts with RBBB were analyzed. Pts were divided into 2 groups: ET or LT. See figure. LVEFs were obtained from ECHO. LVEF ≥ 50% was considered normal. Results: ET: n = 69. LT: n = 39. Mean QRS durations were not different in the 2 groups. ET pts were more likely to have normal LVEF (p < 0.01). See figure. PPV of ET in predicting LVEF ≥50% = 90%; NPV = 71%. Accuracy = 82%. Conclusions: These data, if confirmed, suggest that in pts with RBBB, visual analysis of the QRS complex from the surface ECG using the superimposed median format may provide valuable clues about LV systolic function, and may be clinically useful when ECHO are not readily available.

The effect of cubic stiffness nonlinearity on the vortex-induced vibration of a circular cylinder at low Reynolds numbers

The vortex-induced vibration (VIV) of a circular cylinder elastically supported by linear and cubic springs is investigated numerically at low Reynolds numbers. The cylinder has a low mass ratio and zero structural damping. Nine dimensionless cubic stiffness nonlinearity strength values are considered. It is found that within the parameter space examined, the VIV response for the linear and softening springs can be divided into four regimes, namely the initial, upper, lower and desynchronised regimes. When the softening spring nonlinearity gets stronger, there exist a reduction in the peak amplitude and shifts in the initial-upper branch and upper-lower branch transitions to lower Reynolds number ranges. In contrast, as the hardening spring nonlinearity increases, the response envelope moves to a higher Reynolds number range and the profile of the initial and upper branches becomes smoother with the lower branch gradually disappearing. In the hardening spring case, the beating response is observed near the low end of the initial branch up to the high end of the initial branch. The modulations in the vibration amplitude gradually diminish with increasing Reynolds number. The cubic spring results coincide with those of the linear spring when they are presented with the equivalent reduced velocity. Due to the low Reynolds number range considered, the majority of the vortex shedding is in the 2S mode. The wake in the cases with smaller vibration amplitudes exhibits a single-row configuration. Whereas, a double-row vortex street is mainly observed in the upper branch. Disorders in the wake are found to be associated with beating responses which have larger vibration amplitudes.

Influence of spatial degeneracy on rotational spectroscopy: Three-wave mixing and enantiomeric state separation of chiral molecules

Pulse flip angles are calculated for three-wave mixing, three-state cycles of chiral molecules to produce optimized free induction decay amplitudes proportional to the enantiomeric excess of a sample and to produce optimized degrees of state-specific enantiomeric separation. The calculations account for the spatial degeneracy of the levels involved and the resulting inhomogeneous distribution of transition dipole moments. Cycles of transitions that include R followed by Q followed by P branch transitions display only modest reductions of the calculated optimal signals compared to those calculated if every M component was optimally polarized. Transition cycles P-Q-R are only slightly worse, while the Q-Q-Q cycles are much worse, increasingly so, as the rotational total quantum number is increased.

Innovative scheme for high-repetition-rate imaging of CN radical.

We have employed, to the best of our knowledge, a novel excitation scheme to perform the first high-repetition-rate planar laser-induced fluorescence (PLIF) measurements of a CN radical in combustion. The third harmonic of a Nd:YVO4 laser at 355nm due to its relatively large linewidth overlaps with several R branch transitions in a CN ground electronic state. Therefore, the 355nm beam was employed to directly excite the CN transitions with good efficiency. The CN measurements were performed in premixed CH4-N2O flames with varying equivalence ratios. A detailed characterization of the high-speed CN PLIF imaging system is presented via its ability to capture statistical and dynamical information in these premixed flames. Single-shot CN PLIF images obtained over a HMX pellet undergoing self-supported deflagration are presented as an example of the imaging system being applied towards characterizing the flame structure of energetic materials.

Two-photon-absorption line strengths for nitric oxide: Comparison of theory and sub-Doppler, laser-induced fluorescence measurements.

We discuss the results of high-resolution, sub-Doppler two-photon-absorption laser-induced fluorescence (TPALIF) spectroscopy of nitric oxide at low pressure and room temperature. The measurements were performed using the single-longitudinal mode output of a diode-laser-seeded optical parametric generator (OPG) system with a measured frequency bandwidth of 220 MHz. The measurements were performed using a counter-propagating pump beam geometry, resulting in sub-Doppler TPALIF spectra of NO for various rotational transitions in the (0,0) vibrational band of the A2Σ+ - X2Π electronic transition. The experimental results are compared with the results of a perturbative treatment of the rotational line strengths for the 20 different rotational branches of the X2Π(v″ = 0) → A2Σ+(v' = 0) two-photon absorption band. In the derivation of the expressions for the two-photon transition absorption strength, the closure relation is used for rotational states in the intermediate levels of the two-photon transition in analogy with the Placzek treatment of Raman transitions. The theoretical treatment of the effect of angular momentum coupling on the two-photon rotational line strengths features the use of irreducible spherical tensors and 3j symbols. The final results are expressed in terms of the Hund's case (a) coupling coefficients aJ and bJ for the X2Π(v″ = 0) rotational level wavefunctions, which are intermediate between Hund's case (a) and case (b). Considerable physical insight is provided by this final form of the equations for the rotational line strengths. Corrections to the two-photon absorption rotational line strength for higher order effects such as centrifugal stretching can be included in a straightforward fashion in the analysis by incorporating higher order terms in these coupling coefficients aJ and bJ, although these corrections are essentially negligible for J < 50. The theoretical calculations of relative line intensities are in good agreement both with our experiment and with published experimental results. In addition, the calculated line shapes and relative intensities for closely spaced main branch and satellite transitions are in excellent agreement with our experimental measurements.

Influence of resonant collisions on the self-broadening of acetylene

Iwakuni et al. [Phys. Rev. Lett. 117, 143902 (2016)] have reported an ortho-para alternation of ∼10% in the self pressure broadening coefficients for ro-vibrational lines of the C2H2 transitions in the ν1+ν3 C–H (local mode) overtone band near 197 THz (1.52 μm). These authors attributed this effect to the contribution of resonant collisions, where the rotational energy change of one molecule is exactly compensated by the rotational energy change of its collision partner. Resonant collisions are known to be important in the case of self pressure broadening of highly polar molecules, such as HCN, but have not previously been invoked in the case of nonpolar molecules, such as acetylene, where the long range potential is dominated by the quadrupole-quadrupole electrostatic interaction. In the present work, the simple semiclassical Anderson-theory approach is used to estimate the rates of C2H2–C2H2 rotationally inelastic collisions and these used to predict pressure broadening rates, ignoring other contributions to the broadening, which should not have resonant enhancements. It is found that exactly resonant collisions do not make a major contribution to the broadening and these calculations predict an ortho-para alternation of the pressure broadening coefficients far below what was inferred by Iwakuni et al. The present results are consistent with a large body of published work that reported self-broadening coefficients of C2H2 ro-vibrational transitions that found negligible dependence on the vibrational transition and no even-odd alternation, even for Q and S branch transitions where any such effect is predicted to be much larger than for the P and R branch transitions studied by Iwakuni et al.

Line positions, pressure broadening and shift coefficients for the second overtone transitions of carbon monoxide in argon

Absolute positions and spectral line-shape parameters of carbon monoxide 0→3 band, P branch transitions are reported. The speed-dependent effects and the influence of velocity-changing collisions were taken into account in the fitted line-shape models. For the first time the values of pressure shift coefficients of CO in argon for this band were determined. The measurements were made with the Pound–Drever–Hall-locked frequency-stabilized cavity ring-down spectrometer, with the frequency axis linked through an optical frequency comb to the UTC(AOS) frequency reference based on a hydrogen maser. Achieved uncertainties of line positions are between 70kHz and 420kHz.

Investigation of effective line intensities of trans-HONO near 1255 cm−1 using continuous-wave quantum cascade laser spectrometers

Effective line intensities of P branch transitions of trans-nitrous acid (HONO) in the ν3 H-O-N bending mode near 1255cm−1 have been determined by scaling measured HONO absorption intensities by continuous-wave quantum cascade laser absorption spectroscopy to reference values. Gaseous HONO samples were synthetized in the laboratory using the reaction of H2SO4 and NaNO2 solutions and the heterogeneous formation on surfaces in the presence of ambient water vapor and NO2 gas in a sealed gas sampling bag. The quantification of HONO was performed using a denuder associated with a NOx analyzer. Observed absorption line strengths for the trans conformer are found to be by a factor of approximately 1.17 higher than previously reported line strengths.

Self-referenced, accurate and sensitive optical frequency comb spectroscopy with a virtually imaged phased array spectrometer

We present a cavity-enhanced direct optical frequency comb spectroscopy system with a virtually imaged phased array (VIPA) spectrometer and either a dither or a Pound-Drever-Hall (PDH) locking scheme used for stable transmission of the comb through the cavity. A self-referenced scheme for frequency axis calibration is shown along with an analysis of its accuracy. A careful comparison between both locking schemes is performed based on near-IR measurements of the carbon monoxide ν=3←0 band P branch transitions in a gas sample with known composition. The noise-equivalent absorptions (NEA) for the PDH and dither schemes are 9.9×10(-10) cm(-1) and 5.3×10(-9) cm(-1), respectively.

Asymmetry in Raman Resonant Excitation Profiles of Single-Wall Carbon Nanotubes: The Role of Kohn Anomaly, Optical Transition Order, and State-Mixing

Examination of Raman resonant excitation profiles (REPs) of the radial breathing mode (RBM) and G-band phonons has provided new insights into the coupling between excitons and phonons in single-wall carbon nanotubes (SWCNTs). For example, measurements of REPs of the longitudinal optical (LO) and transverse optical (TO) G-band phonons of highly pure, single semiconducting species SWCNT samples displayed a high degree of asymmetry when comparing the Raman intensity at the incident and scattered Raman resonances for excitation via E22 S. The LO and TO phonon REP asymmetries were explained using a molecular picture as due to a self-interference between Condon and non-Condon terms in the Raman polarizability, due to a vibrational coordinate dependence in transition dipole moment. This results in the observation that the Raman intensity at the scattered resonance is always lower in intensity than that of the incident resonance, a consequence of the failure of the Franck-Condon approximation. This is contrary to the symmetrical G-band REP expected by conventional theory and observed for RBM REPs. More recently, these Raman REP studies were expanded to include metallic armchair species, (5,5) through (8,8), excited via E11 M. Similar asymmetries to those of semiconducting SWCNTs were observed in the TO phonons of these armchair species while no asymmetry was observed for their respective RBM REPs, emphasizing the similarity in the excitonic nature of the optical states of these two electronic types of SWCNTs. In addition, a new model was developed in terms of a condensed matter formalism involving phonon-mediated state-mixing of dark and bright excitonic states to successfully explain the asymmetry in G-band phonon REPs of both semiconductor and armchair SWCNT species. Here, we extend our understanding of this optical phenomenon by considering the roles that Kohn anomaly, optical transition order and phonon-mediated state-mixing play in the degree of asymmetry observed for SWCNT phonon REPs. To examine the effect of the Kohn anomaly, we measured G-band phonon REPs of another electronic type of SWCNT, known as narrow-gap semiconductors (NGS), such as the (7,4) and (10,4) species, whose electronic band structure is similar to that of metallic armchair SWCNTs with the exception of a small band gap on the order of 10 meV. Of special interest in NGS SWCNT structures are the LO phonons, which are strongly frequency-softened and broadened through the Kohn anomaly due to strong coupling of LO phonons with the two Fermi points. Such a strong interaction should further enhance the observed REP asymmetry due to non-Condon-based self-interference. Furthermore, NGS-type SWCNT species, such as the (7,4) and (10,4), possess the additional trigonal warping splitting term in their band structure, which causes each optical transition to split into two, allowing for potential quantum interference between upper and lower branch transitions which may produce further asymmetry. To examine the role of optical transition order on REP asymmetry, we measured RBM and G-band REPs for multiple semiconducting chiralities such as (8,3), (9,1), (5,4), (7,6), (9,4), and (8,6) across multiple optical transitions ranging from E11 S-E44 S. Generally, the degree of asymmetry increased with increasing transition order for the same SWCNT species for the LO phonon. Additionally, we reexamined whether asymmetry exists in RBM REPs of semiconducting species excited via E11 S, where the RBM phonon energy is greater than or equal to the electronic linewidth of the transition, allowing resolution of both incident and scattered resonances of the REP. This was not possible in previous measurements because the electronic linewidths of the optical transitions involved were greater than the RBM phonon energies. Finally, to test the validity of the phonon-mediated state-mixing model, we prepared isotopically pure 12C- and 13C-samples of single chiralities (7,5), (7,6), and (7,7). Using these samples, excited via E22 S for (7,5) and (7,6) and via E11 M for (7,7), we compared the measured G-band phonon REPs for both isotopes of the same chirality. While 13C-SWCNTs look identical to their 12C-counterparts in terms of electronic band structure and optical transition energies, the phonons in their Raman spectra decrease in frequency by a factor of √(12/13) due to the isotope effect. If G-band phonon REP asymmetry is really due to mixing of dark and bright excitonic states, mediated by G-band or K-point phonons, which in turn causes quantum interference between excitonic states or transfer of oscillator strength from one excitonic state to another, then a change in the phonon energy mediating such an interaction should cause a visible change in the degree of asymmetry of the REP for the same chirality. The change in the degree of REP asymmetry provides a measure of the magnitude of state-mixing.

Synchrotron-based far infrared study of the rotation-vibration-inversion spectrum of silacyclobutane below 500 cm−1: The ν29 and ν30 bands

Fourier transform spectra of the four-membered heterocycle silacyclobutane (c-C3H8Si) were recorded in the far infrared region from 100 to 500 cm(-1) with a maximum resolution of 0.000959 cm(-1) using synchrotron radiation from the Canadian Light Source. The two fundamental bands observed in this region correspond to motions best described as the out-of-plane modes related to ring puckering (ν30) at ~158 cm(-1) and SiH2 rocking (ν29) at ~410 cm(-1). Both bands exhibit complex, dense spectral patterns that arise from ring inversion tunneling of the puckered SCB ring through a planar (C(2v)) intermediate configuration. Analysis of these patterns revealed rotation-vibration transitions between states of the same inversion symmetry as well as rotation-vibration-inversion transitions that connect states of different inversion symmetry. Infrared ground state combination differences from 1871 pairs of P and R branch transitions were used to accurately determine the spectroscopic parameters for the tunneling-doubled ground state based on a broad range of quantum levels. With the ground state energy levels well-determined, 8255 infrared transitions were assigned and analyzed to derive the band centers, rotational and centrifugal distortion constants for the inversion split ν29 and ν30 vibrational states. Comparison with the band centers predicted via DFT (B3LYP) and MP2 calculations [6-311++G(2d,2p)] suggests that anharmonic corrections found via perturbation theory typically agree within 2% when compared with the observed spectrum of SCB.

Threshold Alignment Reversal and Circularly Polarized Fluorescence in Rotationally ResolvedH2

Using H2 and D2 targets, we have measured the polarization of Fulcher-band fluorescence resulting from spin-polarized electron-impact excitation of vibrationally and rotationally resolved d 3Π(u) → a 3Σ(g)+ transitions for incident electron energies from 14.3 to 28.5 eV. Near threshold, the linear polarization P1 descends from positive values through zero to negative values, indicating a dynamic production of M(N)=0 states. The circular polarization P3 is measured to be nonzero, indicating the orientation of rotationally resolved molecular states. For Q-branch transitions, P3 is consistent with theory based on Hund's case (b) coupling. The R-branch P3 values do not agree with theory equally well, indicating the effect of Σ-symmetry perturbation of the parent d 3Π(u)+ state.

Direct measurements of collisional Raman line broadening in the S-branch transitions of acetylene (C2H2)

We report direct measurements of the self- and N2-broadened Raman S-branch linewidths of acetylene (C2H2), obtained by employing time-resolved picosecond rotational coherent anti-Stokes Raman scattering spectroscopy. Using broadband 115-ps pump and Stokes pulses (~135 cm(-1) bandwidth) and a spectrally narrowed 90-ps probe pulse (~0.2 cm(-1) bandwidth), Raman-coherence lifetimes are measured at room temperature for the S-branch (ΔJ = +2) transitions associated with rotational quantum number J = 3-25. These directly measured Raman-coherence lifetimes, when converted to collisional linewidth broadening coefficients, differ from the previously reported broadening coefficients extracted from theoretical calculations by 6%-35% for self-broadening for C2H2 and by up to 60% for N2-broadened C2H2.

Methane line parameters in the HITRAN2012 database

The compilation of methane molecular line parameters was updated to include new global analyses and measurements for 12CH4, 13CH4 and 12CH3D. Over 70% of the methane parameters in HITRAN2008 were replaced; existing parameters retained were the microwave lines and the Dyad of 13CH4 near 7μm and ν6 of 13CH3D near 8.7μm, 12CH3D (7–4076cm−1), hot bands of 12CH4 (1887–3370cm−1) and normal sample CH4 (4800–5550cm−1 and 8000–9200cm−1). With a minimum intensity at 296K in units of cm−1/(moleculecm−2) set to 10–37 for the far-IR and 10–29 for the mid- and near-IR, the methane database increased from 290,091 lines in HITRAN2008 to 468,013 lines, and three-fourths of these involved the main isotopologue. For 12CH4 and 13CH4, bands from the ground state were revised up to 4800cm−1. For the first time, 13CH4 and 12CH3D line parameters near 2.3μm were included. Above 5550cm−1, the new compilation was based on empirical measurements. Prior laboratory results were replaced with extensive new measurements using FTIR (5550–5852cm−1), differential absorption spectroscopy (DAS) and Cavity Ring Down Spectroscopy (CRDS) (5852–7912cm−1). Ground state J values for nearly half of the measured lines in this range were obtained, either by confirming quantum assignments of analyses or by using spectra at 80 and 296K. Finally, over 11,000 measured positions, intensities and empirical lower state energies (obtained using cold CH4) were also added for the first time between 10,923 and 11,502cm−1. Available pressure broadening measurements from HITRAN2008 were transferred into the new compilation, but 99% of the lines were given crudely-estimated coefficients. New measured intensities and broadening coefficients were included for far-IR transitions, and high accuracy line positions were inserted for the stronger P, Q and R branch transitions of ν3 at 3.3μm and 2ν3 at 1.66µm.

Direct measurements of collisionally broadened Raman linewidths of CO2 S-branch transitions

We report direct measurements of S-branch Raman-coherence lifetimes of CO(2) resulting from CO(2)-CO(2) and CO(2)-N(2) collisions by employing time-resolved picosecond coherent anti-Stokes Raman scattering spectroscopy. The S-branch (ΔJ = +2) transitions of CO(2) with rotational quantum number J = 0-52 were simultaneously excited using a broadband (~5 nm) laser pulse with a full-width-at-half-maximum duration of ~115 ps. The coherence lifetimes of CO(2) for a pressure range of 0.05-1 atm were measured directly by probing the rotational coherence with a nearly transform-limited, 90-ps-long laser pulse. These directly measured Raman-coherence lifetimes, when converted to collisional linewidth broadening coefficients, differ from the previously reported broadening coefficients extracted from frequency-domain rotational Raman and infrared-absorption spectra and from theoretical calculations by 7%-25%.

Reinvestigation of the ν2 + 2ν3 subband in the overtone icosad of 12CH4 using cavity ring-down (CRD) spectroscopy of a supersonic jet expansion

We report a detailed reinvestigation of the ν2 + 2ν3 combination band of methane 12CH4 centred at (7510.3378 ± 0.003) cm−1 ((225.154263 ± 0.0001) THz) within the icosad of the overtone absorption. A new experimental setup is described, allowing us to carry out cw-laser cavity ring-down spectroscopy (cw-CRDS) at instrumental resolution in the MHz range in seeded supersonic jet expansions down to rotational temperature of 7 K compared to previous cw-CRDS measurements in our group achieving about 50 K in expansions of neat CH4. We provide a careful re-analysis on the basis of our new experimental results for the Q and R branch transitions including data obtained between about 7 and 300 K under various conditions. We resolve previously observed discrepancies of assignments and are able to present a definitive assignment for lines involving angular momentum quantum numbers up to J = 4. The analysis of relative intensities in spectra taken at rotational and effective translational temperatures between about 50 K and less than 10 K indicate conservation of nuclear spin symmetry upon supersonic jet expansion, in agreement with previous results using other techniques and covering other spectral ranges.

BIFURCATION STRUCTURE FOR MODULATED VIBRATION OF STRINGS SUBJECTED TO HARMONIC BOUNDARY EXCITATIONS

In the studies of nonlinear dynamics, phase plan plot is a most commonly used tool for solution characteristics interpretation. Phase plan plot provides an adequate representation of the dynamic characteristics of single solution, but it does not provide information on the interrelation between neighboring solutions; therefore, the evolution of solutions is studied by examining fragmented information of many individual responses. When the solution space becomes complicated, accurate information of the interrelation between responses is essential for an overall comprehension of the characteristics of the solutions. Noticing the characterizing amplitude variation of the limit cycles for typical modulated responses, bifurcation structure was proposed and developed to examine the overall characteristics of the modulated solutions of nonlinear string vibration. The bifurcation structure depicts all solutions in one plot by recording the upper and lower limits of the modulated vibration limit cycles. All kinds of bifurcations and interrelations between typical solutions can be qualitatively and quantitatively identified using the bifurcation structure. In this study, bifurcations and solution interrelations identified and revealed by bifurcation structures include forward and reverse Hopf bifurcations through period-doubling, appearance of isolated solution branch, solution branch transitions between the Hopf branch and isolated branch, appearance of chaotic attractors, chaotic attractor transitions between the Rossler and Lorenz types, and attractor disappearance by boundary crisis.

Absolute measurements of intensities, positions and self-broadening coefficients of R branch transitions in the ν2 band of ammonia

A complete spectroscopic study of 22 ammonia transitions belonging to the ν 2 fundamental band has been undertaken using a high-resolution Fourier transform spectrometer. More than 80 spectra of pure ammonia were recorded at different conditions of temperature (235, 264, and 296 K) and pressure (160–2000 Pa). Special attention was paid to the determination of the absolute wavenumber scale and of the ammonia partial pressure, which allowed to determine absolute positions (8×10 −5 cm −1), absolute intensities (<2%) and self-broadening coefficients (<2%) with high accuracy. Measured intensities show a mean difference of more than 13% compared to intensities extracted from the HITRAN (2008) database while absolute positions are in very good agreement (−3.3×10 −5 cm −1) with database values. Self-pressure shift coefficients are also reported.