Hyperfine singlet-triplet mixing

Doppler-free two-photon transitions to atomic Rydberg levels [251] allow the accurate determination of quantum defects and of level shifts in external fields. Hyperfine structures in Rydberg states of two-electron atoms, such as calcium and singlet-triplet mixing of the valence state 45 and and Rydberg levels have been thoroughly studied by Doppler-free two-photon spectroscopy [252]. 

One example is the measurement of hyperfine quantum beats in the polyatomic molecule propynal HC=CCHO by Huber and coworkers [877]. In order to simplify the absorption spectrum and to reduce the overlap of absorbing transitions from different lower levels, the molecules were cooled by a supersonic expansion (Sect. 4.2). The Fourier analysis of the complex beat pattern (Fig. 7.14) showed that several upper levels had been excited coherently. Excitation with linear and circular polarization with and without an external magnetic field, allowed the analysis of this complex pattern, which is due to singlet-triplet mixing of the excited levels [877, 878]. 

For a discussion of the hyperfine splitting between the components F = I + l and F = 7 - 1, unaffected by singlet-triplet mixing, the 6sns Rydberg series of is chosen. As a typical example. Figure 23... 

For Rydberg states of pure msns configuration, hyperfine-induced singlet-triplet mixing can be easily calculated. " Choosing the energy halfway between the So and S states as zero, the secular equation of the Hamiltonian H = Hq+ Hm [cf. Eq. (16)]... 

Hyperfine-Induced Singlet-Triplet Mixing of Perturbed 6sns So and S Rydberg States of Ba... 

Besides strontium, hyperfine-induced singlet-triplet mixing of msns Sq and Rydberg series has also been investigated in Ca and Contrary to the lighter alkaline earths Ca and Sr, however, the 6sns So and... 

Figure 33. King diagram for unperturbed (upper part) and perturbed (lower part) 6sns Sq Rydberg states. Open symbols refer to experimental isotope shifts, solid ones to data corrected for hyperfine-induced singlet-triplet mixing. The modified isotope shifts shown in Figure 33 were obtained using the data plotted in Figure 32a. (Taken from Ref. 62.)...

Resonance in Singlet-Triplet Mixing of msnd Rydberg Series of Ca, Sr, and Ba, Detected by Hyperfine Structure... 

In particular, for Rydberg states close to the 5d7d D2 valence state located between n = 26 and 27 (cf. Figure 39), deviations from the interval rule are observed, caused by hyperfine-induced singlet-triplet mixing. In order to derive the approximate splitting factors shown in Figure 39, the... 

Singlet-Triplet Mixing and Hyperfine Structure of msnd D2 Rydberg States of Sr and Ba... 

A, Hyperfine Structure and Singlet-Triplet Mixing of 6snp Ba... 

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