PHOTOIONIZATION SPECTROSCOPY OF THE HI MOLECULE: ANGULOAR MOMENTUM COUPLING ACCORDING TO HUND'S CASE(e)

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1992

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Ohio State University

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Below the $^{2}\Pi_{1/2}$ component of the ionic ground state, the photoionization spectrum of HI is strongly influenced by resonance structure due to autoionizing Rydberg series. A rotationally cooled sample hasábeen prepared by a supersonic expansion ($T_{rot}\sim$ 13K), In the energy range form $83500-89200 cm ^{-1}$, VUV radiation is generated by four-wave sum-frequency mixing of pulsed dye-laser radiation in mercury vapor, and used to record the photoionization yield spectrum. The spectral width of the radiation (0.5 cm $^{-1}$) enables us to resolve the rotational structure of the autoionizing Rydberg series. A detailed analysis of the experimental results leads to the assignment of the most prominent structures to 12 Rydberg series converging onto the higher lying $^{2}\Pi_{1/2}$ component of the spin-orbit split $^{2}\Pi$ ionic ground state. Results of a multichannel quantum- defect calculation by H. Lefebvre-$Brion^{1}$\AA compared to the experimental results. This comparison leads to the conclusion that the angular momentum coupling in the HI molecule has to be described in terms of a transition from Hund’s case (c)to Hand’s case (e) coupling for this spectral region.

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$^{1}$A. Mank, M. Drescher, T. Huth-Fere, N. B\""{O}wering, U. Heinzmann and H. Lefebvre-Brion, J. Chem. Phys. 95 1676 (1991)
Author Institution: Department of Chemistry, University of Waterloo; Fakult\'{a}t f\""{u}r Physik, Universit\'{a}t Bielefeld; University Uppsala ISV/Ionphysik, Box 535, S-75121 Uppsala, Sweden

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