Precise Multiphoton Spectroscopy of Small Molecules and Atomic Helium (Physics)

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A program of high resolution measurements on simple atoms and molecules will be continued, concentrating especially on the two.electron systems molecular hydrogen and atomic helium. The experimental methods involve multiphoton excitation of both ground state and metastable species. A pulse.amplified cw dye laser is used to obtain the high powers required for multiphoton excitation while retaining high resolution. The dissociation energy and ionization potential of hydrogen will be determined to a new accuracy, and improved measurements will be made of the structure of helium. These measurements will provide the first stringent tests of calculations of quantum electrodynamic effects in the ground states of two.electron systems. Microwave.optical double resonance will be used to precisely measure transitions between high Rydberg states. A major focus on this research will be the interaction of excited states in hydrogen with the ionization and dissociation continua, including the effects of doubly excited states. The decay of Rydberg states will be studied both with and without external electric fields. Work will continue on the photodissociation of hydrogen very near threshold, which yields detailed information on long.range interactions between atoms.