Lifetime measurements, atomic

Using this optical Keir cell the authors developed a technique to measure the lifetimes of atomic and molecular transitions on a picosecond time scale 138a), See also the reviews by Rentzepis 138b) about ultrafast processes and Merkelo 138c),... 

To discover smaller specific effects on the intramolecular dynamics after attachment of an Ar atom to the benzene molecule, we performed lifetime measurements of single rovibronic states in the 6q band of the benzene-Ar and the benzene-84 Kr complex. No dependence of the lifetime on the J K> quantum number within one vibronic band was found [38]. This is in line with the results in the bare molecule and points to a nonradiative process in the statistical limit produced by a coupling to a quasi-continuum, for example, the triplet manifold. 

Precise measurements on g factors of electrons bound in atomic Hydrogen and the Helium ion 4He+ were carried out by Robinson and coworkers. The accuracies of 3 x 10-8 for the Hydrogen atom [5] and of 6 x 10-7 for the Helium ion [6] were sensitive to relativistic effects. Other measurements of the magnetic moment of the electron in Hydrogen-like ions were performed at GSI by Seelig et al. for Lead (207Pb81+) [7] and by Winter et al. for Bismuth (209Bi82+) [8] with precisions of about 10-3 via lifetime measurements of hyperfine transitions. These measurements were also only sensitive to the relativistic contributions. 

Section 4 describes the atoms consisting of 7r+ and 7r mesons (A2v) and experiments involving their detection and lifetime measurement. The lifetime of A2jt is determined by the charge-exchange process... 

The method for A2v observation and the lifetime measurement were proposed in [30]. In 1994 A2v were observed and a lower limit estimation of their lifetime was given [31,32]. In 1999 the detection of A2v was performed in the DIRAC experiment at CERN and the measurement of ao — a2 with 5% precision is planned for 2002-2003. Also present in section 4 is brief information about atoms, consisting of 7r+ and K (Avk) [30,33] and A2v production in the decays [34]. 

Production of 7r+7r- atoms (and of other hadronic atoms) in inclusive processes was considered and a method of their observation and lifetime measurement was proposed [30]. The atoms are produced in 5-states with the cross section ... 

Gustavsson, M. Lundberg, H. Nilsson,. and Svanberg, S., "Lifetime measurements of excited states of rare-earth atoms using pulse modulation of a CW dye-laser beam,"... 

Atomic Radiative Lifetimes Measured by Pulsed Laser Spectroscopy in the UV/VUV Spectral Region... 

Experimental lifetime measurements on free atoms and ions performed by using pulsed laser excitation in the ultraviolet and vacuum-ultraviolet spectral regions are presented. Different methods of laser pulse generation, atomization and light detection are described. A short summary of results obtained is also given. Future possibilities in determination of lifetimes and transition probabilities in the short wavelengths region are discussed. 

Pulsed laser excitation of evaporated substances and subsequent fluorescence decay detection have been used in the studies reviewed here. In our opinion this is the most convenient method for lifetime measurements in the UVAAJV spectral range. The principal scheme of an experimental set-up is shown in Fig.l. It has been slightly modified in various measurements, but the main parts are the same and correspond to the three tasks atomization, excitation and detection. (The excitation laser pulse has to be of short duration and in the UVA TJV region.) Each of these tasks are discussed more in detail below. 

That allowed to excite atoms to levels otherwise corresponding to direct groundstate transitions with wavelengths <100 nm. In later experiments on N I even higher levels were reached [48], In an experiment on C I two-photon excitation and lifetime measurements were achieved with detection through cascades via a short-lived state [55], a technique also successfully later applied on S I and P I [58,59]. The application of four-wave mixing was demonstrated in experiments on Mg I [29] and later used for studies on Au I, Zn I and S I... 

Further progress in experimental techniques will allow lifetime measurements in neutral and singly ionized atoms to be extended to even shorter wavelengths and lifetimes. Any free neutral and singly ionized atom can be produced in a lasergenerated plasma. For short-lived states, the pump-probe technique allows to overcome the problems with detector response time. A distributed feedback laser pumped by picosecond pulses from a mode-locked NdrYAG laser can serve as a light source. 

A more direct method for lifetime measurements is the delayed coincidence technique [6] in which the time between an initiation event and the emission of a decay product is measured. A schematic diagram of an apparatus used for the measurement of atomic lifetimes is shown in figure BLIP.5. The slope of the graph of the natural log of the number of decay events as a function of time delay gives the lifetime directly. The... 

Chemiluminescence and photoluminescence in diatomic iron oxide, Rb2, and alkali-metal dimers with halogen atoms and metal vapour-oxidant flames,202 203 lifetime measurements of selectively excited states of diatomic hydrides,204 photodissociation of alkali-metal halide vapours,206 spin-orbit relaxation of the HTe ( 2IIi) radical,20 the photodecomposition of metal carbonyl anions such as [Mn(C04)] in the vapour phase,207 and the fluorescence of Rhodamine 6G in the vapour phase 208 have been studied in recent reports. In the last study it was concluded that an insufficient concentration of the fluorescing dye could be maintained in the vapour phase to permit laser action to occur. 

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