Adriana Predoi-Cross

Methane line parameters in HITRAN

Abstract Two editions of the methane line parameters (line positions, intensities and broadening coefficients) available from HITRAN in 2000 and 2001 are described. In both versions, the spectral interval covered was the same (from 0.01 to 6184.5 cm −1 ), but the database increased from 48,033 transitions in 2000 to 211,465 lines in 2001 because weaker transitions of 12 CH 4 and new bands of 13 CH 4 and CH3D were included. The newer list became available in 2001 in the “Update” section of HITRAN. The sources of information are described, and the prospects for future improvements are discussed.

Broadening, shifting, and line asymmetries in the 2←0 band of CO and CO–N2: Experimental results and theoretical calculations

We have measured the room temperature, widths, pressure shifts, and line asymmetry coefficients for many transitions of the first overtone band of CO and CO perturbed by N2. The broadening coefficients were obtained with an accuracy of about 1%. The pure CO profiles have been fitted by a Voigt profile while the CO–N2 spectral profiles have been fitted with a Lorentz and an empirical line shape model (HCv) that blends together a hard collision model and a speed-dependent Lorentz profile. In addition to the Voigt, Lorentz, and HCv models, we have added a dispersion profile to account for weak line mixing. The line broadening and shift coefficients are compared to semiclassical calculations employing a variety of intermolecular interactions. The line asymmetry results are compared to line mixing calculations based on the energy corrected sudden (ECS) model. The results indicate that effects other than line mixing also contribute to the measured line asymmetry.

Broadening and line mixing in the 20 00←01 10, 11 10←00 00 and 12 20←01 10 Q branches of carbon dioxide: Experimental results and energy-corrected sudden modeling

Using both a difference frequency spectrometer and a Fourier transform spectrometer, we have measured transitions in the 12 (2)0<--01 (1)0 band of carbon dioxide at room temperature and pressures up to 19 atm. The low-pressure spectra were analyzed using a variety of standard spectral profiles, all with an asymmetric component to account for weak line mixing. For this band, we have been able to retrieve experimental line strengths and the broadening and weak mixing parameters. In this paper we also compare the suitability of the energy-corrected sudden model to predict mixing in the two previously measured Q branches 20 (0)0<--01 (1)0, the 11 (1)0<--00 (0)0, and the present Q branch of pure CO(2), all at room temperature.

Experimental and theoretical study of N2-broadened acetylene line parameters in the ν1 + ν3 band over a range of temperatures

N2-broadened line widths and N2-pressure induced line shifts have been measured for transitions in the ν1 + ν3 band of acetylene at seven temperatures in the range 213–333 K to obtain the temperature dependences of broadening and shift coefficients. For the room-temperature spectra the line mixing effects have been also investigated. The Voigt and hard-collision line profile models were used to retrieve the line parameters. All spectra were recorded using a 3-channel tuneable diode laser spectrometer. The line-broadening and line-shifting coefficients as well as their temperature-dependence parameters have been also evaluated theoretically, in the frame of a semi-classical approach based on an exponential representation of the scattering operator, an intermolecular potential composed of electrostatic quadrupole–quadrupole and pairwise atom–atom interactions as well as on exact trajectories driven by an effective isotropic potential.

The far-infrared spectrum of 12C2HD

The infrared spectrum of 12C2HD has been studied using synchrotron radiation at the far-infrared beam line, Canadian Light Source, Saskatoon, Canada. The spectra were recorded at a resolution of 0.00096 cm−1 in the 60 to 360 cm−1 range using a Bruker IFS 125 Fourier transform spectrometer. In total, 821 vibration rotation lines were observed and assigned to the P(J), Q(J) and R(J) transitions of the ν 5 ← ν 4 difference band and associated hot bands with J″ up to 35 and (ν 4 + ν 5) up to 3. These new transitions were analysed together with 4518 transitions involving bending states with (ν 4 + ν 5) up to 3 available in the literature. The spectroscopic parameters obtained from the fit reproduce 4909 transitions with a standard deviation of 0.00028 cm−1. The ν 5 ← ν 4 bands of 13CH12CD and 12CH13CD were also detected and analysed.

Theoretical calculations for line-broadening and pressure-shifting in the ν 1 + ν 2 + ν 4 + ν 5 band of acetylene over a range of temperatures

Semiclassical calculations of self-broadening and self-induced pressure shift coefficients in the ν 1 + ν 2 + ν 4 + ν 5 band of C2H2 have been performed by considering, in addition to the main electrostatic quadrupole–quadrupole interaction, a simple anisotropic dispersion contribution, leading to results in overall satisfactory agreement with recent measurements [C. Povey, A. Predoi-Cross and D.R. Hurtmans, J. Mol. Spectrosc., 268, 177 (2011)]. In these calculations we have used the mean relative velocity and also considered the Maxwell–Boltzmann distribution of relative velocities. From the theoretical results obtained at different temperatures ranging from 200 to 350 K, we have determined temperature exponents of the broadenings using a simple power law, as well as coefficients of empirical linear and quadratic temperature dependences for the line shifts. These theoretical exponents and linear coefficients, derived from averaging over the distribution of velocities and from the mean thermal velocity, are significantly different and they are compared with those obtained from measurements of broadening coefficients and line shifts performed in a comparable temperature range [C. Povey, A. Predoi-Cross and D.R. Hurtmans, J. Mol. Spectrosc., 268, 177 (2011)]. The theoretical variation of the self-shifts with temperature is not linear and can be well fitted by a quadratic polynomial.

High-resolution synchrotron-based Fourier transform spectroscopy of in the 120–350 cm−1 far-infrared region

The Fourier transform spectrum of the isotopologue of methanol has been recorded in the 120–350 cm−1 far-infrared region at a resolution of 0.00096 cm−1 using synchrotron source radiation at the Canadian Light Source. The study, motivated by astrophysical applications, is aimed at generating a sufficiently accurate set of energy level term values for the ground vibrational state to allow prediction of the centres of the quadrupole hyperfine multiplets for astronomically observable sub-millimetre transitions to within an uncertainty of a few MHz. To expedite transition identification, a new function was added to the Ritz program in which predicted spectral line positions were generated by an adjustable interpolation between the known assignments for the and isotopologues. By displaying the predictions along with the experimental spectrum on the computer monitor and adjusting the predictions to match observed features, rapid assignment of numerous sub-bands was possible. The least squares function of the Ritz program was then used to generate term values for the identified levels. For each torsion-K-rotation substate, the term values were fitted to a Taylor-series expansion in powers of J(J + 1) to determine the substate origin energy and effective B-value. In this first phase of the study we did not attempt a full global fit to the assigned transitions, but instead fitted the sub-band J-independent origins to a restricted Hamiltonian containing the principal torsional and K-dependent terms. These included structural and torsional potential parameters plus quartic distortional and torsion–rotation interaction terms.

Doppler broadening thermometry of acetylene and accurate measurement of the Boltzmann constant

In this paper, we present accurate measurements of the fundamental Boltzmann constant based on a line-shape analysis of acetylene spectra in the ν1 + ν3 band recorded using a tunable diode laser. Experimental spectra recorded at low pressures (0.25 - 9 Torr), have been analyzed using a Speed Dependent Voigt model that takes into account the molecular speed dependence effects. This line-shape model reproduces the experimental data with good accuracy and allows us to determine precise line-shape parameters for the P(25) transition of the ν1 + ν3 band. From the recorded spectra we obtained the Doppler-width and then determined the Boltzmann constant, k(B).

The infrared spectrum of 13C2H2 in the 60–2600 cm−1 region: bending states up to v 4 + v 5 = 4

The vibration–rotation spectra of 13C substituted acetylene, 13C2H2, have been recorded in the region between 60 and 2600 cm−1 at an effective resolution ranging from 0.001 to 0.006 cm−1. Three different instruments were used to collect the experimental data in the extended spectral interval investigated. In total 9529 rotation vibration transitions have been assigned to 101 bands involving the bending states up to v tot = v 4 + v 5 = 4, allowing the characterization of the ground state and of 33 vibrationally excited states. All the bands involving states up to v tot = 3 have been analyzed simultaneously by adopting a model Hamiltonian which takes into account the vibration and rotation l-type resonances. The derived spectroscopic parameters reproduce the transition wavenumbers with a RMS value of the order of the experimental uncertainty. Using the same model, larger discrepancies between observed and calculated values have been obtained for transitions involving states with v tot = 4. These could be satisfactorily reproduced only by adopting a set of effective constants for each vibrational manifold, in addition to the previously determined parameters, which were constrained in the analysis.

Low-pressure line shape study of acetylene transitions in the ν 1 + ν 2 + ν 4 + ν 5 band over a range of temperatures

In this study we have retrieved the self-broadened widths, self-pressure-induced shifts, and Dicke narrowing coefficients for 20 R-branch transitions in the ν1 + ν2 + ν4 + ν5 band of acetylene. The spectra were recorded using a three-channel diode laser spectrometer, a temperature-controlled cell of fixed length and a second, room temperature cell. The soft collision (Galatry) and hard collision (Rautian) profiles with inclusion of line mixing effects were used to retrieve the line parameters. We determined the temperature dependencies for line broadening, shift, and Dicke narrowing coefficients. We performed comparisons between our retrieved line parameters and published line parameters for acetylene transitions.