Research Staff: Charles Chackerian, Jr. and Lawrence P. Giver

The focus of our efforts have been on determining absolute line intensities for the carbon monoxide, CO, and nitric acid, HNO₃, molecules.

For CO we have made very accurate measurements on the 3-0 and 2-0 vibrational bands. Work on the former has been published We have incorporated the results of these measurements with quantum-mechanical calculations of numerical wave functions to obtain a revised electric-dipole-moment function for CO. This function will soon be used by us to correct the many thousands of line intensities listed in the HITRAN database for normal CO and its important isotopic modifications. The results of this work are used where CO is monitored using infrared spectroscopy, when the sun is used in observations as a background light source, in modeling the atmospheres of cool stars such as brown dwarfs, and in the analysis of combustion sources.

The challenge in obtaining accurate intensity parameters for nitric acid has been in obtaining a pure sample of gas. The thermal decomposition of HNO₃ occurs in a short period compared to the period required to record a high-resolution interferogram. We have been able to obtain a pure gas sample by synthesizing HNO₃ at the spectrometer and then flowing this gas through the spectrometers absorption cell while the interferogram was recorded. In this way we have obtained a high-quality set of high-spectral resolution spectra between 800 cm^-1 and 3600 cm^-1 which we will analyze for line intensities. We have also obtained low-resolution (0.112 cm^-1) spectra over the same spectral region which we have analyzed for spectral absorbency at ~0.056 cm^-1 intervals. Our work on HNO₃ has relevance for its monitoring in the atmosphere and in interpreting the spectral signatures of aerosols and other species, which occur in overlapping spectral regions.

Point of Contact: Charles Chackerian, Jr., 650/604-6300, cchackerian@mail.arc.nasa.gov