Fluorescence spectra satellite lines

The dominant decay branches which result from Is ionization in neon are shown in Fig. 2.5. The fluorescence decay concerns the dipole transitions 2p - Is, shown in the upper row. In the X-ray nomenclature they are called K-L2 3 transitions where the dash is used to separate the initial and final hole-states. These transitions are also called Ka, 2 transitions (see Fig. 2.2). As can be seen in the experimental fluorescence spectrum shown in Fig. 2.6, in addition to these K-L2 3 main transitions there are other lines called satellites. These satellites result from KL-L2 and even KL2-L3 transitions where the dash again separates initial and final hole-states, e.g., KL-L2 radiative transitions start with two holes, one in the K-shell, and one in the L-shell, and they end with two holes in the L-shell. 

Figure 2.6 Fluorescence spectrum following Is ionization in neon. The most intense line represents the unresolved doublet of main lines, K-L2 3, the structures with lower intensity are due to accompanying satellite transitions where the initial state contains one (KL - L2) or even two (KL2 - L3) additional holes in the L-shell. From [Kes73].

Qualitative analysis is, in principle, very simple with XRF and is based on the accurate measurement of the energy, or wavelength, of the fluorescent lines observed. Since many WD-XRF spectrometers operate sequentially, a 20 scan needs to be performed. The identification of trace constituents in a sample can sometimes be complicated by the presence of higher order reflections or satellite lines from major elements. With energy-dispersive XRF, the entire X-ray spectrum is acquired simultaneously. The identification of the peaks, however, is rendered difficult by the comparatively low resolution of the ED detector. In qualitative analysis programs, the process is simplified by overplotting so called KLM markers onto... 

Molecules in the collisionally populated levels m) can decay by the emission of fluorescence or by further collisions. In the LIF spectrum new lines then appear besides the parent lines, which are emitted from the optically pumped level (Fig. 8.7). These new lines, called collision-induced satellites contain the complete information on the collision process that has generated them. Their wavelength X allows the assignment of the upper level m) = + An, 7 + A7), their intensities yield... 

Such determinations of rotationally inelastic integral cross sections ajcm for collision-induced transitions in excited molecules obtained from measurements of satellite lines in the fluorescence spectrum have been reported for a large variety of different molecules, such as I2 [983, 984], Li2 [985, 986], Na2 [987], or NaK [988]. For illustration, the cross section a (A7) for the transition 7 7 + A7 in excited NaJ molecules induced by collisions Na + He are plotted in Fig. 8.8. They rapidly decrease from a value a(AJ = 1) 0.3 nm to a(AJ = 8) 0.02 nm. This decrease is essentially due to energy and momentum conservation, since the energy difference AE = E(J A7) — E(J) has to be transferred into the kinetic energy of the collision partners. The probability for this energy transfer is proportional to the Boltzmann factor exp[—A /(A r)] [989]. 

While collision-induced transitions in excited electronic states can be monitored through the satellite lines in the fluorescence spectrum (Sect. 8.2.2), inelastic collisional transfer in electronic ground states of molecules can be studied by changes in the absorption spectrum. This technique is particularly advantageous if the radiative lifetimes of the investigated rotational-vibrational levels are so long that fluorescence detection fails because of intensity problems. 

The fluorescence excitation spectrum, Fig. 10, suggests that single molecules without are most hkely to be encountered to the red of the main line, whereas single molecules containing a C nucleus should be abundant with high probability between the satellite lines. In Fig. 11 the FDMR spectra in zero-field of the ( F>- Z)) transition for three different molecules are shown. The location of the optical absorption for the three molecules was to the red of the main line for molecule I, in between satellites 4 and 5 for molecule n and to the blue of satellite 5 for molecule III. The insets in each figure depict the position of the C substitution of each molecule. Whereas molecule I contains C nuclei exclusively, molecule II contains a... 

Fig. 12.7. Collision-induced satellite lines in the laser-induced fluorescence spectrum. Example of rotational and vibrational transitions from the (v =6,J =43) level in the state of Na2- The parent line is 20-fold off scale...

Fig. 8. Collision-induced satellite spectrum of Naj around X = 5290 A, due to fluorescence originating from rotational levels populated by collision from the V = 6, / = 43 level in the state, which was excited by the X = 4880 A argon laser line. (From ref.

In addition to LIF resonant two-photon ionization (Sect. 1.4) can also be used for the sensitive detection of collision-induced rotational transitions. This method represents an efficient alternative to LIF for those electronic states that do not emit detectable fluorescence because there are no allowed optical transitions into lower states. An illustrative example is the detailed investigation of inelastic collisions between excited N2 molecules and different collision partners [995]. A vibration-rotation level (v, J ) in the a Jig state of N2 is selectively populated by two-photon absorption (Fig. 8.10). The collision-induced transitions to other levels v + An, / + AJ) are monitored by resonant two-photon ionization (REMPI, Sect. 1.2) with a pulsed dye laser. The achievable good signal-to-noise ratio is demonstrated by the collisional satellite spectrum in Fig. 8.10b, where the optically pumped level was v = 2, J = 7). This level is ionized by the P(l) parent line in the spectrum, which has the signal height 7.25 on the scale of Fig. 8.10b. 

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