Chad Povey

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.

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).

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.

Experimental air-broadened line parameters in the\bm{ u}\textsubscript band of CH\textsubscriptD

In this study, we report the first experimental measurements of air-broadening and air-induced pressure-shift coefficients for approximately 378 transitions in the ν2 fundamental band of CH3D. These results were obtained from analysis of 17 room-temperature laboratory absorption spectra recorded at 0.0056 cm–1 resolution using the McMath–Pierce Fourier transform spectrometer located on Kitt Peak, Ariz. Three absorption cells with path lengths of 10.2, 25, and 150 cm were used to record the spectra. The total sample pressures ranged from 0.129 × 10–2 to 52.855 × 10–2 atm with CH3D volume mixing ratios of approximately 0.0109 in air. The spectra were analyzed using a multispectrum nonlinear least-squares fitting technique. We report measurements for air pressure-broadening coefficients for transitions with quantum numbers as high as J′′ = 20 and K = 15, where K′′ = K′ ≡ K (for a parallel band). The measured air-broadening coefficients range from 0.0205 to 0.0835 cm–1atm–1 at 296 K. All the measured pressure...