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Published October 2009 | Published
Journal Article Open

Laboratory measurements and theoretical calculations of O_2 A band electric quadrupole transitions


Frequency-stabilized cavity ring-down spectroscopy was utilized to measure electric quadrupole transitions within the ^(16)O_2 A band, b^1Σ^+_g ← X^3Σ^-_g(0,0). We report quantitative measurements (relative uncertainties in intensity measurements from 4.4% to 11%) of nine ultraweak transitions in the ^NO, ^PO, ^RS, and ^TS branches with line intensities ranging from 3×10^(−30) to 2×10^(−29) cm molec.^(−1). A thorough discussion of relevant noise sources and uncertainties in this experiment and other cw-cavity ring-down spectrometers is given. For short-term averaging (t<100 s), we estimate a noise-equivalent absorption of 2.5×10^(−10) cm^(−1) Hz^(−1/2). The detection limit was reduced further by co-adding up to 100 spectra to yield a minimum detectable absorption coefficient equal to 1.8×10^(−11) cm^(−1), corresponding to a line intensity of ~2.5×10^(−31) cm molec.^(−1). We discuss calculations of electric quadrupole line positions based on a simultaneous fit of the ground and upper electronic state energies which have uncertainties <3 MHz, and we present calculations of electric quadrupole matrix elements and line intensities. The electric quadrupole line intensity calculations and measurements agreed on average to 5%, which is comparable to our average experimental uncertainty. The calculated electric quadrupole band intensity was 1.8(1)×10^(−27) cm molec.−1 which is equal to only ~8×10^(−6) of the magnetic dipole band intensity.

Additional Information

© 2009 The American Physical Society. Received 15 July 2009; published 21 October 2009. The research at the Jet Propulsion Laboratory JPL, California Institute of Technology, was performed under contract with the National Aeronautics and Space Administration.

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Published - Long2009p6351Phys_Rev_A.pdf


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August 21, 2023
October 19, 2023