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 Title: SATURATION DIP MEASUREMENTS OF HIGH-J TRANSITIONS IN THE v1+v3 BAND OF C2H2: ABSOLUTE FREQUENCIES AND SELF-BROADENING Author(s): Sears, Trevor Contributor(s): Hall, Gregory; Twagirayezu, Sylvestre Subject(s): Lineshapes, collisional effects Abstract: _x000d_ % begin{document} _x000d_ % maketitle _x000d_ begin{wrapfigure}[10]{r}{0.32textwidth}_x000d_ vspace{-12pt}_x000d_ includegraphics[width=0.32textwidth]{PvGamma_mbar_units.eps}_x000d_ vspace{-16pt}_x000d_ end{wrapfigure}_x000d_ Saturation dip spectra of acetylene in the $v_1 + v_3$ band have been obtained for rotational lines with $J = 31-37$ inclusive, using a diode laser referenced to a frequency comb. The estimated accuracy and precision of the measurements is better than 10 kHz in 194 THz. Data were obtained as a function of sample pressure to investigate the broadening of the saturation features. _x000d_ The observed line shapes are well modeled by convolution of a fixed Gaussian transit-time and varying Lorentzian lifetime broadening, textit{i.e.} a Voigt-type profile. The lines exhibit a significantly larger collisional (lifetime) broadening than has been measured in conventional Doppler and pressure-broadened samples at ambient temperatures. The figure shows the fitted Lorentzian width versus sample pressure for P($31$). The slope of this plot gives the pressure broadening coefficient, $gamma_{self} = 9.35(13)$ MHz/mbar. For comparison, the coefficient derived from conventional Doppler and pressure broadened spectra for this transition is $2.7$ MHz/mbarfootnote{J. Molec. Spectrosc. textbf{209}, 216-227 (2001) and J. Quant. Spectrosc. Rad. Transf. textbf{76}, 237-267 (2003)}. The sub-Doppler broadening coefficients are all significantly larger than the conventionally measured ones, due to the increased importance of velocity-changing collisions. The measurements therefore give information on the balance between hard phase- or state-changing and large cross-section velocity-changing collisions. _x000d_ _x000d_ textbf{Acknowledgments}: Work at Brookhaven National Laboratory was carried out under Contract No. DE-SC0012704 with the U.S. Department_x000d_ of Energy, Office of Science, and supported by its Division of Chemical Sciences, Geosciences and Biosciences within the Office of Basic Energy Sciences. _x000d_ % end{document}_x000d_ Issue Date: 6/21/2017 Publisher: International Symposium on Molecular Spectroscopy Citation Info: APS Genre: CONFERENCE PAPER/PRESENTATION Type: Text Language: English URI: http://hdl.handle.net/2142/97183 DOI: 10.15278/isms.2017.WJ06 Date Available in IDEALS: 2017-07-27
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