High-resolution spectroscopy and quantum-defect model for the gerade triplet np and nf Rydberg states of He{sub 2}
Photoionization spectra and Rydberg-state-resolved threshold-ionization spectra of the gerade triplet np Rydberg states of {sup 4}He{sub 2} located in the vicinity of the X{sup +2}Σ{sub u}{sup +}(ν{sup +} =0) ionization threshold were recorded from the 2sσa{sup 3}Σ{sub u}{sup +} metastable state. An accuracy of 0.01 cm{sup −1} was achieved for the experimental term values of the observed Rydberg states. The data were combined with spectroscopic data on low-lying triplet np and nf Rydberg states from the literature to derive energy- and internuclear-distance-dependent eigenquantum-defect parameters of multichannel quantum-defect theory (MQDT). The MQDT calculations reproduce the experimental data within their experimental uncertainties and enabled the derivation of potential-energy curves for the lowest triplet p Rydberg states (n = 2–5) of He{sub 2}. The eigenquantum-defect parameters describing the p -f interaction were found to be larger than 0.002 at the energies corresponding to the high-n Rydberg states, so that the p -f interaction plays an important role in the autoionization dynamics of np Rydberg states with ν{sup +} = 0. By extrapolating the experimental term values of triplet np Rydberg states of {sup 4}He{sub 2} in the range of principal quantum number n between 87 and 110, the positions of the (ν{sup +} = 0, N{sup +} = 3) and (ν{sup +} = 0, N{sup +} = 5) levels of the ground state of {sup 4}He{sub 2}{sup +} were determined to lie 70.937(3) cm{sup −1} and 198.369(6) cm{sup −1}, respectively, above the (ν{sup +} = 0, N{sup +} = 1) ground rotational level.
- OSTI ID:
- 22255131
- Journal Information:
- Journal of Chemical Physics, Vol. 140, Issue 6; Other Information: (c) 2014 Author(s); Country of input: International Atomic Energy Agency (IAEA); ISSN 0021-9606
- Country of Publication:
- United States
- Language:
- English
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