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Title: Lineshape of rotational spectrum of CO in 4He droplets
Authors: Zillich, Robert E.
Whaley, K. Birgitta
von Haeften, Klaus
First Published: 3-Mar-2008
Publisher: American Institute of Physics
Citation: Journal of Chemical Physics, 2008, 128 (9), 4303.
Abstract: In a recent experiment the rovibrational spectrum of CO isotopomers in superfluid helium-4 droplets was measured, and a Lorentzian lineshape with a large line width of 0.024 K (half width at half maximum) was observed [von Haeften et al., Phys. Rev. B 73, 054502 (2006)]. In the accompanying theoretical analysis it was concluded that the broadening mechanism may be homogeneous and due to coupling to collective droplet excitations (phonons). Here we generalize the lineshape analysis to account for the statistical distribution of droplet sizes present in nozzle expansion experiments. These calculations suggest an alternative explanation for the spectral broadening, namely, that the coupling to phonons can give rise to an inhomogeneous broadening as a result of averaging isolated rotation-phonon resonances over a broad cluster size distribution. This is seen to result in Lorentzian lineshapes, with a width and peak position that depend weakly on the size distribution, showing oscillatory behavior for the narrower size distributions. These oscillations decrease with droplet size and for large enough droplets (~104) the line widths saturate at a value equal to the homogeneous line width calculated for the bulk limit.
DOI Link: 10.1063/1.2833979
ISSN: 1089-7690
Type: Article
Rights: The following article appeared in the Journal of Chemical Physics, 2008, 128 (9), 4303, and may be found at Doi:10.1063/1.2833979. Copyright 2008 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics.
Appears in Collections:Published Articles, Dept. of Physics and Astronomy

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