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 Title: FREQUENCY-COMB REFERENCED SPECTROSCOPY OF _4 AND _5 HOT BANDS IN THE _1+_3 COMBINATION BAND OF C2H2 Author(s): Twagirayezu, Sylvestre Contributor(s): Hall, Gregory; McRaven, C.; Sears, Trevor; Cich, Matthew Subject(s): Mini-symposium: High-Precision Spectroscopy Abstract: Doppler-free transition frequencies for nub{4} and nub{5} hot bands in the band of C$_{2}$H$_{2}$ have been measured using saturation dip spectroscopy with an extended cavity diode laser referenced to a frequency comb. The frequency accuracy of the measured transitions, as judged from line shape model fits and the spectrometer stability, is better than 30 kHz. This is some 2-3 orders of magnitude improvement on the accuracy and precision of previous measurements of the line positions derived from the analysis of high-resolution Fourier transform infrared absorption spectra. The data were analyzed by determining the upper state energies, using known lower state level positions, and fitting them to a $J(J+1)$ polynomial expansion to identify perturbations. The results reveal that the upper rotational energy level structure is mostly regular but suffers $J-$localized perturbations causing level shifts between one and several hundred MHz. These perturbations are due to accidental near degeneracies with energy levels of the same $J$ and larger bending vibrational excitation. textbf{Acknowledgements}: We are most grateful to Prof. D.S Perry (U. of Akron) and Prof. M. Herman (U. Libre de Bruxelles) for providing us with detailed results from their work and helpful discussions. Work at Brookhaven National Laboratory is funded by the Division of Chemical Sciences, Geosciences and Biosciences within the Offices of Basic Energy Sciences, Office of Sciences, U.S. Department of Energy under Contract Nos. DE-AC02-98CH10886 and DE-SC0012704. Issue Date: 24-Jun-15 Publisher: International Symposium on Molecular Spectroscopy Citation Info: ACS Genre: CONFERENCE PAPER/PRESENTATION Type: Text Language: English URI: http://hdl.handle.net/2142/79209 Date Available in IDEALS: 2016-01-05
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