Ultra-Sensitive Optical Measurements of High-J Transitions in the O2 A-band

 

Daniel K. Havey, David A. Long, Charles E. Miller, and Joseph T. Hodges

Process Measurements Division, Nanoscale and Optical Metrology Group, Chemical Science and Technology Laboratory, NIST Gaithersburg, MD 20899.

 

               The reliability of high-J line parameters in the HITRAN database has a direct affect on the uncertainty budget of experiments aiming to utilize spectroscopic probing to study highly rotationally excited molecules.  Ultra-cold collision dynamics of O2(Erot), specifically, has recently been suggested as an intriguing but experimentally demanding system.  Subtle deviations of the HITRAN database, as revealed by experiments, may be amplified depending on how far in J the parameters are extrapolated.  Our goals in this study are (I) to provide the highest-J spectroscopic measurements of line intensities and widths for the primary isotope of O2 in the A-band region and (II) to understand how the line parameters compare to, and build on, what is contained in the HITRAN database.  These experiments are challenging because the lines are some of the weakest ever observed in the laboratory and require ultra-sensitive optical detection methods.  Understanding specifically how the HITRAN line intensities in the A-band region deviate, as a function of J, from experiment also has a more general significance.  It allows for a test of currently used Hönl-London factors for O2, which describe the J-dependence of the line intensities.  This could prove useful in studies involving other spectral regions.  We have measured transitions between J’ = 32 and 50 (self-broadened) and J’ = 32 and 42 (air-broadened).  Our highest J measurements probe lower states having rotational energies of ~3775 cm-1, ~40% higher than the most extensive measurements to date.


 

CATEGORY: Chemistry

 

Mentors Name:  Joseph T. Hodges

Process Measurements Division, Chemical Science and Technology Laboratory

Bldg. 221 Rm. A127 Mailstop 8360

Tel: (301)-975-2605

Email:  joseph.hodges@nist.gov

 

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