Rydberg states metastability

Purely optical excitation is possible for alkali and alkaline earth atoms. For most other atoms the transition from the ground state to any other level is at too short a wavelength to be useful. To produce Rydberg states of such atoms a combination of collisional and optical excitation is quite effective. A good example is the study of the Rydberg states of Xe by Stebbings et al.24 As shown in Fig. 3.5, a thermal beam of Xe atoms is excited by electron impact, and a reasonable fraction of the excited atoms is left in the metastable state. Downstream from the electron excitation the atoms in the metastable state are excited to a Rydberg state by pulsed dye laser excitation. 

Fig. 3.5 Schematic diagram of the apparatus using electron impact excitation to the Xe metastable state followed by laser excitation to Rydberg states (from ref. 24).

A beam of metastable Xe atoms is excited to a Rydberg state or photoionized and the product Xe+ ions are expelled by a field pulse from 2-5 /is later and impinge upon a position sensitive detector. When the metastable Xe is photoionized the pattern reflects the geometry of the metastable Xe beam, and the same is true when Xe+ is produced by attachment of the electron from a Xe 60f state to SF6. Apparently, there is no deflection of the Xe + by the SF6 . However, at low n,n< 40, the pattern of Xe+ detected is twice as broad as the metastable beam, indicating deflection of the Xe+ ion by the SF6-. As expected, the deflections of the Xe+ become more pronounced at lower n. 

While electrons in conventional beams have velocities too high to have large cross sections, thermal electrons have large cross sections for state changing collisions with Rydberg atoms, and these collisions have been studied in a systematic fashion. Specifically, metastable He atoms in a stationary afterglow have been excited to specific Rydberg states with a laser.37 38 The populations of... 

Increased metastable n=2 Ps rates should allow laser excitation to higher states, in particular highly excited Rydberg states. The signature of such a transition could be the reduction of La counts, if a n=2 fine structure transition is driven simultaneously. 

Massick and Breckenridge [97Mas] have carried out Resonance Enhanced Two-Photon (R2PI) spectroscopy starting from the two metastable states Mg(3s3pjt Ar( IIo+, IIo-). They ended in four Rydberg states ... 

Herring et al. [98Her] have recorded rotationally resolved LIE speetra of the Rydberg systems S/tt Ilg <— a and 5/(7 Eg <— a where 4sa a is the first excited (metastable) state of the neutral At2 complex, and the designation of the Rydberg states follows the usual nomenclature nlX for the outer electron (s —> u for / even and s—> g for I odd). The At2 ground state core reads The following parameters were obtained from the... 

Staemmler and coworkers have treated a number of open-shell systems in close connection with experimental problems, such as the photodissociation of H20 ° or the Penning ionization of water by metastable He. Further work is concerned with Rydberg states of H4 and Hj, rotational barriers about C=C double bonds and ionization potentials. ... 

As is well known, the first-order Doppler effect can be eliminated by irradiating a well-collimated atomic beam perpendicular to a laser beam. Since tunable, narrow-band cw dye laser radiation of sufficiently short wavelength is not yet available, in most cases the excitation of atomic Rydberg states by a one-photon transition from the ground state is not feasible. The population of Rydberg states, however, might proceed from excited, metastable or even short-lived states which are continuously pumped by an additional laser beam. The latter approach was chosen by... 

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