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 Title: TIME- AND FREQUENCY-DOMAIN SIGNATURES OF VELOCITY CHANGING COLLISIONS IN SUB-DOPPLER SATURATION SPECTRA AND PRESSURE BROADENING Author(s): Hall, Gregory Contributor(s): Sears, Trevor; Dagdigian, Paul; Forthomme, Damien; Xu, Hong Subject(s): Lineshapes, collisional effects Abstract: We have combined experimental and theoretical approaches to the competition between elastic and inelastic collisions of CN radicals with Ar, and how this competition influences time-resolved saturation spectra. Experimentally, we have measured transient, two-color sub-Doppler saturation spectra of CN radicals with an amplitude chopped saturation laser tuned to selected Doppler offsets within rotational lines of the A-X (2-0) band, while scanning a frequency modulated probe laser across the hyperfine-resolved saturation features of corresponding rotational lines of the A-X (1-0) band. A steady-state depletion spectrum includes off-resonant contributions ascribed to velocity diffusion, and the saturation recovery rates depend on the sub-Doppler detuning. The experimental results are compared with Monte Carlo solutions to the Boltzmann equation for the collisional evolution of the velocity distributions of CN radicals, combined with a pressure-dependent and speed-dependent lifetime broadening. Velocity changing collisions are included by appropriately sampling the energy resolved differential cross sections for elastic scattering of selected rotational states of CN (X). The velocity space diffusion of Doppler tagged molecules proceeds through a series of small-angle scattering events, eventually terminating in an inelastic collision that removes the molecule from the coherently driven ensemble of interest. Collision energy-dependent total cross sections and differential cross sections for elastic scattering of selected CN rotational states with Ar were computed with Hibridon quantum scattering calculations, and used for sampling in the Monte Carlo modeling. \ _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. 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/2142/96949 DOI: 10.15278/isms.2017.WJ07 Date Available in IDEALS: 2017-07-27
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