Long-Lived, Energetic States of Small Molecules: Spectroscopy, Pattern Recognition, and Formation/Destruction Mechanisms

摘要

The formation, deactivation, and detection mechanisms of atoms and molecules in metastable electronically excited states are, in general, ill characterized. Yet the chemical and photophysical properties of such states are relevant to Air Force Missions in communication, upper atmosphere modeling, and high-speed vehicle tracking, and identification. The capabilities of a multispectral molecular beam apparatus have been demonstrated on the electronic spectrum of acetylene in the energy region of the first excited singlet state (S1), which is isoenergetic with high vibrational levels of the metastable triplet states (T1, T2, T3). This apparatus records two kinds of spectra (UV-LIF and SEELEM, respectively UltraViolet Laser Induced Fluorescence and Surface Electron Ejection by Laser Excited Metastables) simultaneously, which sample complementary groups of short- and long-lived rovibronic states. The most remarkable findings are: (i) UV-LIF spectra contain fully assignable eigenstates with dominant S1 or T3 character, where the T3 character acts as a 'doorway' into states of dominant T1, T2 character that appear in SEELEM spectra; (ii) SEELEM spectra contain eigenstates that are rotationally fully assignable, regular in level pattern and relative intensity, yet vibrationally ergodic. Ergodicity in T23 coexists with doorway behavior in T1. Ergodicity, contrary to naive expectations, results in regular appearing spectra.