Excitation and Emission Properties of Molecular Nitrogen for Earth's Thermosphere

Space Environment Technologies, Pacific Palisades CA

Investigators

Abstract

The investigators will combine experimental measurement and theoretical calculation to determine molecular nitrogen excitation and emission properties that are critical to the rate processes of nitrogen rich thermospheres. Molecular nitrogen is transparent to solar radiation from the infrared to the far ultraviolet where the forbidden Lyman-Birge-Hopfield and Vegard Kaplan band systems show weak, discrete absorption transitions. Strong absorption of solar radiation occurs in the extreme ultraviolet where the singlet ungerade electronic states show strong discrete blended structure. These states are closely spaced in energy and are strongly coupled. Many of them are strongly predissociative and a major source of chemical radicalization in the atmosphere. The strong coupling among the ungerade states results in very large rotational dependence of transition dipole matrix elements and predissociation yields. The strong rotational dependence in cross sections and predissociation yields requires that laboratory measurements must be translated to projected atmospheric temperature through modeling to avoid large errors. The impact of the strong rotational dependence has not been considered in many atmospheric models. Predissociation yields will be determined from a comparison of emission and excitation cross sections. The measured emission cross sections, together with the already measured, high resolution photoabsorption cross sections, will be utilized to determine the diabetic electronic transition moments. A coupled-channel model will be used to analyze the measurements and calculate spontaneous transition probabilities and predissociation yields. The research in this program connects the community concerned with the understanding of the thermosphere with researchers in laboratory geophysics and theoretical atomic and molecular physics. The program addresses fundamental physical properties of molecular nitrogen, which are critical to understanding the upper atmospheres of Earth, Titan and Triton. As such, the results of the work are applicable beyond the restricted targets identified here, and become a knowledge base for a broad range of disciplines. The program has extensive participation of undergraduate, graduate students and post-doctoral scholars.